mott macdonald resa report final issue

Guernsey AirportRunway End Safety Areas

Pavement Rehabilitation ProjectReview of RESA Options

January 2011

284350 ITD ITA 01 B

C:\Documents and Settings\rud17635\Desktop\284350 GSY\L - Reports and Other Documents\03 Drafts\Mott MacDonald RESA

28 January 2011

Guernsey Airport Runway End Safety Areas

Pavement Rehabilitation Project Review of RESA Options

January 2011

Mott MacDonald, Mott MacDonald House, 8-10 Sydenham Road, Croydon CR0 2EE, United Kingdom T +44(0) 20 8774 2000 F +44 (0) 20 8681 5706, W www.mottmac.com

Treasury & Resources Department, States of Guernsey, Sir Charles Frossard House, La Charroterie, St Peter Port, Guernsey GY1 1FH


Mott MacDonald, Mott MacDonald House, 8-10 Sydenham Road, Croydon CR0 2EE, United Kingdom T +44(0) 20 8774 2000 F +44 (0) 20 8681 5706, W www.mottmac.com

Revision Date Originator Checker Approver Description A 14 Jan 2011 GDR - - FIRST DRAFT (incomplete)

B 20 Jan 2011 GDR - - FINAL DRAFT

C 26 Jan 2011 GDR TC AG 2nd FINAL DRAFT

D 28 Jan 2011 GDR TC AG FINAL

Issue and revision record

This document is issued for the party which commissioned it and for specific purposes connected with the above-captioned project only. It should not be relied upon by any other party or used for any other purpose.

We accept no responsibility for the consequences of this document being relied upon by any other party, or being used for any other purpose, or containing any error or omission which is due to an error or omission in data supplied to us by other parties

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Chapter Title Page

Executive Summary i

1. Introduction 1

2. Regulation 3

2.1 Airport Regulation ____________________________________________________________________ 3

2.1.1 ICAO ______________________________________________________________________________ 3

2.1.2 Nature and Application of Regulatory Rules ________________________________________________ 4

2.1.3 States of Guernsey ___________________________________________________________________ 5

2.1.4 CAA _______________________________________________________________________________ 5

2.1.4.1 CAA EMAS Policy ____________________________________________________________________ 5

2.1.5 FAA _______________________________________________________________________________ 8

2.1.5.1 FAA EMAS Policy ____________________________________________________________________ 8

3. RESA Requirements 9

3.1 Purpose of Runway End Safety Areas ____________________________________________________ 9

3.1.1 Guernsey Runway Excursion History ____________________________________________________ 11

3.2 Runway Classification ________________________________________________________________ 13

3.2.1 ICAO _____________________________________________________________________________ 13

3.2.2 CAA ______________________________________________________________________________ 15

3.2.3 FAA ______________________________________________________________________________ 17

3.3 Runway Width ______________________________________________________________________ 18

3.4 Runway Strip Requirements ___________________________________________________________ 18

3.4.1 Cleared and Graded Area _____________________________________________________________ 20

3.5 RESA Requirements _________________________________________________________________ 21

3.5.1 RESA Length _______________________________________________________________________ 21

3.5.2 RESA Width ________________________________________________________________________ 22

3.5.3 RESA Gradients ____________________________________________________________________ 23

3.5.4 Existing RESAs at Guernsey Airport _____________________________________________________ 24

3.5.5 Overrun Role of a RESA ______________________________________________________________ 27

3.5.6 Undershoot Role of a RESA ___________________________________________________________ 28

3.6 ACRP Report 3 _____________________________________________________________________ 29

3.7 EMAS Enhanced RESA ______________________________________________________________ 33

3.7.1 EMAS Construction __________________________________________________________________ 35

3.7.2 Basis of EMAS Design _______________________________________________________________ 37

3.7.3 Design Aircraft for EMAS Bed __________________________________________________________ 39

3.7.4 Performance of Overrun EMAS Bed _____________________________________________________ 39

3.7.5 Equivalent RESA Length ______________________________________________________________ 40

3.7.6 Undershoot Scenario _________________________________________________________________ 42

3.7.7 Light Aircraft _______________________________________________________________________ 42

3.7.8 Impact of Vehicles on EMAS ___________________________________________________________ 42

3.7.9 Maintenance and Service Life __________________________________________________________ 42

Content



3.7.10 EMAS Damage and Repair ____________________________________________________________ 43

3.7.10.1 Impact on ILS Localiser Signal _________________________________________________________ 43

3.7.10.2 Replacement Blocks _________________________________________________________________ 44

4. Runway Development Options 45

4.1 Pavement Rehabilitation Options _______________________________________________________ 45

4.2 Option A (with EMAS) ________________________________________________________________ 46

4.2.1 Supplier’s EMAS RESA Proposal _______________________________________________________ 46

4.2.2 RPS Option A (with EMAS) ____________________________________________________________ 48

4.3 Standard FAA EMAS Proposal _________________________________________________________ 49

4.3.1 Cost ______________________________________________________________________________ 51

4.3.2 Further EMAS Options _______________________________________________________________ 51

4.4 Option C (Grass RESA)_______________________________________________________________ 52

4.5 230 + 200 RESA Proposal ____________________________________________________________ 52

4.5.1 Cost ______________________________________________________________________________ 53

4.5.2 Further Options _____________________________________________________________________ 53

4.6 Option C2 _________________________________________________________________________ 54

4.6.1 Cost ______________________________________________________________________________ 55

5. MM Conclusions re EMAS RESA 56

i



Most aircraft accidents occur during the landing or take-off phases of flight and the probability of such an event is highest near to the runway ends. Regulation requires a number of clearances to be provided on the ground and in the airspace around a runway to allow an aircraft to safely manoeuvre and to mitigate the consequences of such accidents or incidents when they occur. The particular issues of concern that are being addressed in this report are where aircraft overrun the runway end on landing or take-off, or undershoot the start of the runway on landing.

Overrun and undershoot protection is conventionally provided by the provision of cleared and graded areas at each runway end. These are known as Runway End Safety Areas (RESAs), which are provided to at least the minimum dimensions, but wherever practical, to the recommended dimensions of the regulator. RESAs are normally grassed. These can be substantial areas, 150m wide, that often extend at least 300 m beyond the runway ends. This means the platform that surrounds the runway at Guernsey Airport would need to be at least 2,100 m long.

The existing runway and the airport land around it does not provide RESAs to the CAA’s recommended dimensions. Part of the proposed Pavement Rehabilitation Project at Guernsey Airport is to bring these runway end protection areas into compliance with the CAA’s recommendations as required by the Director of Civil Aviation (DCA).

At Guernsey and at many other airports it is very difficult to provide the necessary area of land required and a combination of shorter and narrower RESAs may be the best that can be provided, but that does not reduce the risk of an overrun or undershoot event. Indeed, where the site is constrained, the runway length is also likely to be limited, and that is likely to increase the probability of an overrun.

However, an alternative to a grass RESA exists in the form of an arrestor bed, which is designed to bring an overrunning aircraft to a controlled stop in a shorter distance. The most effective and safest arresting system that has been developed in recent years is an Engineered Material Arresting System (EMAS). This was developed in the Unites States under the auspices of the Federal Aviation Authority (FAA) and in October 2010, the UK Civil Aviation Authority (CAA) published is policy for the use of EMAS enhanced RESAs in the UK.

Executive Summary

ii



The CAA’s new policy is to permit the use of an EMAS enhanced RESA where a 240 m long RESA cannot be reasonably provided. The EMAS installation is to comply with the FAA’s specification and guidance and be approximately equivalent to a 240 m long overrun RESA.

This report was commissioned in the light of the publication of this policy to consider the various RESA options associated with the Pavement Rehabilitation Project and whether or not the proposed Option A (with EMAS) was acceptable, or may need to be amended to be made acceptable.

Under the CAA’s Licensing provisions, for the Code 3C category of runway in use at Guernsey (and also if it were to be extended at some future date and became a Code 4C category), a RESA starts at the end of the runway strip, which extends 60 m beyond the runway ends. The minimum dimensions for the RESA are 90 m long by 90 m wide and the recommended dimensions are 240 m long by 150 m wide1. Because the RESA dimensions stated in the regulations are determined by the category of runway and not by any consideration of the aircraft operations on the runway, they must be considered a simplified safety provision, which does not relate to any specific probability of such an event occurring at Guernsey Airport.

An assessment of the risks that specifically apply at Guernsey may result in an acceptable level of risk being achieved by the provision of RESAs with dimensions between the CAA’s minimum and recommended values. Such an assessment would require a statistical analysis of the numbers and performance of aircraft in operation at the airport and their respective overrun and undershoot histories. Such a study could be undertaken, but is not part of the scope of this report. In addition, not all the relevant statistical information is available for this design approach and approximations would still have to be made.

Irrespective of the design of RESA provided, it is not practical to provide RESAs that are large enough to capture all potential runway ends accidents. As with most aviation safety provisions, the intention is to provide protection for the vast

_________________________

1 equates to width of runway strip cleared and graded area at runway ends

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majority of events, bearing in mind the potential consequences and the financial and environmental impacts associated with each solution.

In considering the specific roles of a RESA in accommodating overruns on take-off or landing and undershoots on landing, we note that the approximate risks are that: (a) landing-related overruns are general about 5 times more likely to occur than take-off related overruns and (b) all types of overruns are also about 4 times more likely to occur than undershoots.

In the particular case of an EMAS enhanced overrun area, the FAA determined their policy by reference to their studies that showed that 90% of overruns exit the runway end at speeds of 70 knots or less and that most come to rest between the extended runway edges within 1,000 ft (300 m) of the runway end.

The FAA, CAA, DCA and ourselves are all satisfied that an overrunning aircraft entering into an EMAS bed (within its design parameters) will be passively brought to a controlled stop with minimum injury to its occupants and minimum damage to the aircraft itself.

The consequences are more predictable than when an aircraft overruns onto a grassed RESA, even if that is built to the full recommended dimensions, because deceleration on grass depends entirely on the braking performance of the aircraft and the performance of a grass RESA can also be materially changed by the nature and consistency of the sub-soil and the presence of water, snow or ice.

Experience with EMAS enhanced RESAs installations is limited to the past 10 years. In each of the seven overrun events that have occurred to date an EMAS bed, the aircraft has been stopped within the bed, recovered with minimum damage and the occupants have been uninjured. While over many more years, there have been hundreds of overrun events worldwide onto grass RESAs, some have resulted in major damage to the aircraft, injuries and, on occasion, even the death of some of the persons on board. We conclude that this is not just due to the range of events, types of hazard and the difference in the respective sample sizes, but that the design of an EMAS bed, which limits the stress on the aircraft undercarriage, is inherently safer for aircraft that enter into it.

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There have been two relevant overrun events at Guernsey Airport since 1999 and the Airport, the CAA and the DCA wish to see the RESA dimensions improved and if practicable, meet the CAA’s recommended dimensions as part of the pavement rehabilitation project. Achieving compliance with current regulations is the normal expectation of regulators and designers when upgrading a runway.

The intention is to enhance the RESAs, preferably to the full recommended length, but the availability of the required land at both ends, and the width of the site at the west end, are restricted. Possibly for this reason, the Airport’s proposals do not seek to improve the RESA width. However, the CAA’s recommendations are that the RESA width should equal the width of the cleared and graded part of the runway strip, which at the ends of the strip is 150 m wide.

At the east end of the runway at Guernsey, the existing RESA length is about 80 m, which is less than the minimum dimension. At the west end of the runway, the existing RESA length is about 120 m. There is insufficient land within the existing airport boundary to provide 240 m long by 150 m wide RESAs and maintain existing declared runway distances. Improving existing RESA lengths with the existing site would result in a reduction in the runway declared distances.

A reduction in the declared runway distances for take-off and landing would have a significant and unacceptable effect on commercial air transport operations at Guernsey Airport and this has been accepted by the States.

The airport has acquired additional land at the west end of the runway and has applied to acquire some more. However, even with this extended site it will not be possible to provide 240 m long by 150 m wide RESAs at both ends and maintain existing declared runway distances. There are significant difficulties in obtaining more land to the east or the west, which would require substantial road diversions and earthworks and have further impacts on local properties.

The site is therefore constrained and, in consultation with the DCA, we have concluded that the provision of shorter EMAS enhanced RESAs would be consistent with the CAA’s policy.

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Grass RESAs of the full recommended dimensions cannot be achieved, but lesser dimensions, depending on their value, may still be acceptable.

Land is available to provide the FAA’s standard 180 m long EMAS enhanced overrun area and its 180 m long undershoot area at each end of the runway and there is insufficient reason to accept a sub-standard solution that is shorter than this.

In considering EMAS installations we have also concluded that:-

A 180 m long standard FAA overrun area is consistent with the CAA’s policy;

The EMAS bed shall be the width of the runway (45 m), plus the width of the side ramps;

The EMAS bed should be located at the far end of the RESA and designed to stop the commercial aircraft types anticipated at Guernsey Airport;

The EMAS bed shall be laid on a paved base that is set back from the runway end and shall be wider than the bed to allow vehicle access around the bed. The distance between the runway end and the EMAS bed shall also be paved. The pavement shall be designed to resist propwash and jet blast and the occasional passage of an overrunning or undershooting aircraft;

The EMAS bed should be located within a 150 m wide RESA to the extent that land for this width is available;

If the bed may need to be repositioned in the future to facilitate an extended runway, the bed should be designed to allow the relocation of as many of the aerated concrete blocks as can be permitted;

If the installation is located at the far end of a potential future extended runway, but designed for lighter aircraft than those that may operate in the future, then the rear of the EMAS bed should be brought forward to allow it to be lengthened as necessary to stop heavier aircraft types; and

Unless it is possible to design a repair scenario that will ensure the bed can be reinstated after a run-off event in no more than 45 days, then a stock of approximately 20% of the blocks for a single bed should be provided and stored on or near the airport.

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In considering grass RESA solutions we have also concluded that:-

Unless a risk assessment can demonstrate otherwise and if at all practicable, the overrun RESA should be 240 m long;

To be consistent with the EMAS options on this constrained site, the undershoot RESA could be reduced to a minimum length of 120 m;

The RESA widths should be 150 m wide to the extent that land for this width is available.

According to the FAA information, an EMAS installation would be effective in protecting against about 90% of overruns, whether on landing (approximately 60% of all runway end events and thus the most probable event), or overruns on take-off (approximately 20% of all events), but EMAS does not provide any benefit in the event of an undershoot (approximately 20% of all events).

Unlike the FAA, the CAA do not propose different lengths for overrun and undershoot RESAs, but unless a shorter undershoot RESA is accepted, there would be no spatial benefits at Guernsey if an EMAS bed were to be installed at one or both ends of the runway. Given that the statistical risk of undershoot is much lower than for an overrun, we can see case for permitting a shorter undershoot RESA when land availability is restricted. However, a shorter undershoot RESA is not just about scenarios with an EMAS bed, where the EMAS bed provides no undershoot benefits. The same logic would also apply to schemes with a conventional grass RESA on a restricted site.

We have not identified any supporting material to suggest that a RESA of less than the CAA’s recommended width is not necessary and therefore a width of at least 150 m should be provided unless it is impracticable to do so. In this context, we recognise that it is impractical to provide a 150 m width throughout its entire length of some RESA options at the west end of the Guernsey runway.

We are also of the opinion that the width of the runway CGA and the RESA should not instantaneously reduce in the general direction of aircraft travel. To do so may result in an instantaneous change from a safe overrun area to a hazardous overrun area and/or risk striking an obstacle square on. If the width of the CGA and RESA gradually reduces (as the CGA is permitted to do between its 210 m

vii



and 150 m overall widths), then the pilot will be directed back towards the safer CGA or RESA surface, or if he is unable to steer the aircraft, it will meet the boundary at a shallow angle, which in many circumstances should result in a less severe impact. Where the 150 m width cannot be achieved, then the RESA should taper down to no less that 90 m, although if it is necessary to trim off the furthest corners in order to provide the full recommended 240 m length, then that too should be acceptable, because the probability of an aircraft entering that part of the RESA area is the lowest.

Numerous Pavement Rehabilitation Options have been considered in developing the current proposals and three Options have remained under consideration:

Option A (with EMAS) within the existing site boundary

Option C (grass RESA) extended site to the west – requires additional land

Option C1 (grass RESA) extended site to the west – within land acquired to date

Option A (with EMAS)

DRB Associates as Agents to Zodiac, the US EMAS manufacturers, have proposed an overrun RESA that finishes about 115 m from both runway ends, with an EMAS bed commencing 10.7 m from the runway ends. This only provides RESAs that are less than the minimum 90 m RESA length and less than the RESA lengths presently provided at the existing Guernsey runway (117 m at the west end and 78 m at the east end).

RPS have drawn a similar proposal, but (as recommended by the FAA) with the EMAS bed located at the rear of the available RESA lengths.

While both concepts will stop aircraft entering the bed, they are not adequate for aircraft entering into the RESA on either side of the EMAS bed and are both inadequate in length as an undershoot RESA for movements in the opposite direction.

We have concluded that an EMAS enhanced overrun RESA extending at least 180m from the runway end (120 m RESA + 60 m strip) is consistent with CAA

viii



policy and would be consistent with the FAA’s length of undershoot RESA2. That is therefore our preferred EMAS enhanced length for the overrun and undershoot areas. A 150 m RESA width also meets the FAA and CAA requirements.

We have therefore produced sketches of a 1,463 m long Runway with a standard 180 m long FAA EMAS installation at each end.

The overall length would be at least 1823m. This dimension would extend from the localiser aerial at the east end to just short of La Mare Road at the west end. It’s capital cost would be approximately £6m more than Option C. If spare blocks were required, this would add a further £0.7m. The site would have to be extended at both the east and west ends if it were necessary to extend the runway in the future.

Option C (grass RESA)

The length of the RESAs provided by Option C are less than 240m at each end. The proposed scheme offers 240m at the west end and just under 200m at the east end. We accept that these are reasonable distances for the operations at Guernsey, although the distribution between the east and west end could be altered to reflect the more hazardous topography beyond the east end. However, the proposed RESA width is just 90m and thus not enhanced over the existing width. It would be readily possible to provide the recommended width at the east end and that can also be provided for part of its length at the west end.

We recommend that if selected, this scheme is amended to do this and estimate that the additional capital cost will be about £0.5m.

The RESA lengths at each end could be equalised to around 220 m, which would displace the runway a further 20 m to the west and add approximately a further £0.5m to its capital cost. Due to the westerly bias in the direction of operations, the case for this is not strong.

_________________________

2 For a runway with vertical approach guidance

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Option C1 (grass RESA)

We have also considered Option C1, but note that the undershoot RESA length at the east end remains at its existing short length (approximately 78m). This we consider inadequate, given that alternative schemes have been produced that provide a RESA at the east end of just less than 200m.

We have therefore also sketched up a scheme that is similar to Option C1, but which provides 120 m long by 150 m wide undershoot RESAs and full 240 m long by 150 m wide overrun RESAs at each end. We refer to this as Option C2. This insets the thresholds 120 m at each end and provides the 1463 m runway distances. When compared with Option C, this option offers full length, full width overrun RESAs, but shorter undershoot RESAs. It happens to be entirely consistent with the FAA’s requirements for their equivalent category of runway. The overall length of paved runway is slightly more than for Option C and consequently, its capital cost would be approximately £1.5m more than Option C.

Conclusions

All three of the above modified options provide improved RESA dimensions, although none provide the full recommended lengths and widths. They are all compliant with the CAA’s regulations and where applicable, the CAA’s new policy regarding the use of EMAS enhanced RESAs.

They all offer a 1463 m landing distance (LDA) and in most instances the declared TORA and ASDA will either also be 1463 m, or where the existing east end of the runway is to the east of the new threshold, slightly longer take-off distances for Runway 27.

Each has a different overall east-west dimension and they all have their eastern end located adjacent to the Runway 09 ILS localiser aerial array,

Consequently, the extent to which they require additional land to the west varies.

Table 1.1 below compares the three compliant options

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Table 1.1: Comparison of Compliant Options

MM Option Standard EMAS Modified Opt C Option C2

RESA DIMENSIONS:

Rwy 27 Undershoot Area 120m RESA + 60m Strip 197m RESA + 60m Strip 120m RESA + 60m Strip

Rwy 27 Overrun Area 120m RESA incl EMAS + 60m Strip

240m RESA + 60m Strip 240m RESA + 60m Strip

Rwy 09 Undershoot Area 120m RESA + 60m Strip 240m RESA + 60m Strip 120m RESA + 60m Strip

Rwy 09 Overrun Area 120m RESA incl EMAS + 60m Strip

197m RESA + 60m Strip 240m RESA + 60m Strip

RESA Width 150m 150m, but RESA at west end tapers down to 90m

150m

RUNWAY DISTANCES:

Paved Runway (excl blast pads) 1505 m 1588 m 1583 m

Rwy 09 and Rwy 27 LDA 1463 m 1463 m 1463 m

Rwy 09 TORA and ASDA 1463 m 1463 m 1463 m

Rwy 27 TORA and ASDA 1505 m 1588 m 1505 m

Runway 09 Threshold Moved 45m west Moved 125m west Moved 170m west

LAND TAKE:

Overall E-W dimension (ILS to ILS) 1823 m 2013 m 1943 m

Within Site Boundary No No No

Additional Land Requirements at west end

Existing land required only up to La Mare Road

Existing land required plus additional land up to Rouette de la Tourelle

Existing land required (i.e. up to field boundary west of Rouette de la Tourelle)

La Mare Road Can remain Open Closed Closed

Rouette de la Tourelle Unaffected Improved Improved

Future Runway Extension EMAS relocated

Land required up to Rouette de la Tourelle

No additional land at west end

Land required up to Rouette de la Tourelle

COST:

Additional Capital Cost £6m £0.5m £1.5m

Source: Mott MacDonald

1



Mott MacDonald has been appointed by the Treasury and Resources Department of the States of Guernsey to advise on the current options for the provision of enhanced Runway End Safety Areas (RESAs) at Guernsey Airport.

This report must be considered in connection with the Pavement Rehabilitation project that has been prepared by the Public Services Department. This project is to address the state of the existing runway, which has now well exceeded its design life. In addition, the project is to address aspects of the existing runway’s vertical alignment and some safety clearances, where it does not comply with current regulatory requirements and to also improve aspects of the taxiway and apron pavements. Several runway improvement options were considered to meet these objectives and a short list of preferred options developed.

Extending the length of the runway at this time is not part of the project, because there is no demonstrable need at this time. However, the view of the Public Services Department, the Airport management and their previous advisors is that the need to extend the runway (by up to 300m) may arise in the foreseeable future and that its is prudent to safeguard for such a requirement when planning this project.

This proposed project has been considered by the States of Deliberation.

In their development of the runway improvement options, the Public Services Department, in consultation with the airport management and their technical advisors have considered the technical and regulatory requirements, potential environmental impacts and costs of each scheme.

If it is extended, a longer runway will require the extension of the paved surface at either one or both ends.

In addition, a runway sits within a protected area, called a runway strip and the category of the operations at Guernsey also requires the provision of Runway End Safety Areas (RESAs) at each runway end to minimise the potential impacts to the aircraft and on the ground of an aircraft undershooting or overrunning the runway. The existing RESAs are shorter and narrower than current regulatory requirements for the class of runway at Guernsey. Extending the existing RESAs either requires shortening the existing length of runway available for landing and take-off or extending the overall length of the protected area, again at one or both ends, or a combination of both.

1. Introduction

2



Shortening the useable runway length would seriously restrict some of the aircraft operations that could continue to take place at Guernsey Airport. In particular, the commercial operations would find themselves having to take-off or land at lighter weights, or be restricted to the use of fewer aircraft types. This has been rejected by the Airport and its advisors as unacceptable - a decision endorsed by the States of Guernsey as neither being in the interests of the aircraft operators, nor in the interests of the residents of Guernsey.

Thus extending the RESAs, with or without a runway extension, will require extending the total length of the land required for the runway platform. This will require the acquisition of additional land at one, or both ends of the runway. This may also result in the relocation the start and end points of that part of the runway used for take-off and that part of the runway for landing (not necessarily the same) in one or both directions.

For both reasons, the Airport has already purchased land to the west of the runway. It is appropriate to also note that while that land slopes down to the west, the land at the east end of the runway slopes away even more steeply, such that any extension on that side would require a considerable quantity of civil engineering works at a substantial cost.

There is however a possible alternative technical solution to the need to extend the RESAs. That is to install an Engineered Materials Arresting System (EMAS), which is designed to bring to a halt an overrunning aircraft in a reasonably predictable and controllable manner that may result in little or no damage to that aircraft, or injury to the persons on board. This material has been developed in the United States and has already proved to be useful at a number of airports where it would be impractical to extend the existing RESAs and it has also proved effective in containing several overruns. Virtually all the installation and operational experience to date is in the US, where the FAA is the regulator and often also provides the funding for its installation.

However, the installation and maintenance of an EMAS system has a significant cost and there is now a CAA policy statement that will determine and restrict its use in the UK. When the previous report was made to the States of Deliberation, the opinion of the UK CAA on the application of EMAS as a substitute for RESA had not been published and the risk was that it may not prove as useful in practise as the proponents of the system were suggesting. The purpose of this report is to update that previous advice, based on the subsequent recent statements made by the UK CAA in this regard.

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2.1 Airport Regulation

The States of Guernsey have determined that the technical regulation of aviation and airports is to be undertaken in accordance with the standards and recommendations of the UK Civil Aviation Authority (CAA) under the auspices of the Director of Civil Aviation (DCA).

Ordinarily, we would not need to consider regulation beyond these two bodies, but this report is to consider the latest position in regard to the provision of improved RESAs at Guernsey Airport and the possible use of an Arrestor Bed system to enhance the performance of the existing RESAs. Because the latter has been developed in the USA, we must also consider the operational, regulatory and financial environment in which it has been developed.

The following is a brief explanation of the wider regulatory environment that is relevant to formulating this report.

2.1.1 ICAO

Most countries have agreed that it is in the interests of safety and regularity to have a uniform approach to the design, construction, operation and maintenance of aircraft, navigation aids, airports and supporting services. The International Civil Aviation Organisation (ICAO) provides an International regulatory framework for civil aviation. It is a United Nations body and the UK is a Contracted State, which means it has committed itself to comply with ICAO regulations. ICAO also promulgates common systems for considering environmental impacts, training, security and charges.

ICAO’s requirements for Aerodrome Design and Operations are published in Annex 14 to the Convention on International Civil Aviation. These are in the form of Standards (which shall be complied with) and Recommendations (which should be complied with). Collectively known by the acronym SARPs, these are mostly prescriptive in nature.

Each Contracting State then promulgates the Annex 14 requirements via its own local legislative and administrative frameworks. Some just republish Annex 14 as its own regulatory requirement. Some also quote Annex 14, but go on to state a list of specific exceptions. Other States produce their own documents that are based on the Annex 14 SARPs, but the text is completely re-written and there may be significant changes to the detail and the way a number of Annex 14 provisions are enacted. The UK and the USA are two such States that take the latter course.

2. Regulation

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2.1.2 Nature and Application of Regulatory Rules

ICAO Annex 14 and its country-specific equivalent regulations describe a complex set of provisions for the design and operation of aerodromes. It is therefore inevitable that some of the rules are simplified representations of the underlying technical principles. The ICAO SARPs are also focussed on protecting aircraft and their occupants. It is therefore important to also recognise that they do not necessarily cover every relevant aspect of safe, practical or commercially viable operations and that other design and operational considerations may apply that arise outside of the provisions of the ICAO SARPS (e.g. local Health & Safety laws, environmental impacts, or financial constraints).

Two relevant examples of simplified rules in Annex 14 are the shapes of the Runway Strip and the RESA, which are both rectangular in plan. Mott MacDonald is not aware of any evidence that suggests that the risk profile for run-offs, overruns, or undershoots is rectangular in shape. Indeed, in undertaking background studies for this report, the indications are that the risk profile for an accident in a RESA is similar to a Public Safety Zone, which is triangular rather than rectangular in shape. We would also suggest that the profile of the ground and the nature of obstacles and other hazards at and just beyond the boundary of such areas should also be a valid consideration when assessing the risks and potential consequences of an aircraft leaving the runway, even if they are not specifically mentioned in Annex 14.

There are also substantial step changes in the Annex 14 requirements that occur as a result of moving from one runway classification to another. Again, relevant examples are the dimensions of runway strips and obstacle limitation surfaces which depend on the classification (termed the Runway Code) that applies. In this regard, how runways are classified varies between ICAO, the UK CAA and the US FAA.

Mott MacDonald would expect all new airport developments to comply with ICAO standards. We also expect all new airport developments to comply with the ICAO recommendations (or the local recommendations that stem from Annex 14) unless it is impractical to do so.

However, we note that the tendency amongst regulators is to require full compliance with both the ICAO standards and recommendations, even though it is often impractical to fully comply with every recommendation. This is, of course, the cautious approach, but we are concerned that this approach assumes the requirements to be perfect and can reduce safety regulation to a clerical process, rather that give due consideration to the actual circumstances and risks that apply.

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2.1.3 States of Guernsey

As stated at the start of this section, the States of Guernsey recently decided to change the way it regulates its aviation sector and has appointed a Director of Civil Aviation (Mr Fergus Woods) who also now acts in the same capacity for Jersey.

The DCA is charged with applying regulation in accordance with the requirements of the UK CAA and it is therefore their regulations that we have to consider as the primary regulatory requirements in this study.

2.1.4 CAA

The UK CAA depart from ICAO Annex 14 in both the structure and some significant details of their equivalent regulation, which is CAP 168. This document promulgates their provisions for the Licensing of Aerodromes.

There are several relevant areas where the CAA’s CAP 168 departs from the provisions of ICAO’s Annex 14. These include:

The definition of the runway Code Number classification;

The provision of a “lower third” Code 3 category;

Guidance regarding matters to be considered when deciding on appropriate RESA dimensions

Unless stated otherwise, any reference to regulatory requirements or SARPs in this document refers to UK CAA requirements.

The relevant aspects of CAP 168 are explained in more detail in section 3.2.2 below.

2.1.4.1 CAA EMAS Policy

In August 2010, the UK CAA published their draft policy and on 5th October 2010 their current policy, on the application of Engineered Materials Arresting Systems (EMAS). This was a consequence of an evaluation of the FAA research, system performance specifications and guidance material developed in the United States and an examination review of the only EMAS system currently approved by the FAA (the ESCO/Zodiac EMAS). The CAA have accepted that this EMAS system is effective in arresting aircraft overruns.

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The CAA’s published policy is:

a. to permit the installation of EMAS at UK licensed aerodromes as an alternative where a 240 m RESA cannot be achieved;

b. to accept the FAA performance specification and guidance material as suitable for use in EMAS design in the UK, subject to a suitable safety assessment by each aerodrome on their own circumstances (i.e. where to site the system, dimensions, operating conditions etc.);

c. to permit EMAS to be located within the runway strip or RESA as determined by the design assessment;

d. to permit an increase in runway declared distances that can be achieved from the installation of EMAS only where installation of EMAS has provided the equivalent to a 240 m RESA and 60 m strip end (a full length EMAS for the design size aircraft).

The CAA also state that they will develop guidance material on the assessment and oversight of EMAS as required, based on existing (FAA) information, data from the system manufacturers and experience as UK applications are examined.

Point a above clearly states that an EMAS enhanced RESA is only accepted where a 240 m long RESA cannot be achieved. We understand that means cannot reasonably be achieved. Therefore the CAA would not permit its use merely as an alternative to a conventional (grass) RESA. We note there is no reference to the RESA width.

Figure 2.1: Option C Pavement Rehabilitation Scheme

Source: Guernsey Airport

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The various Pavement Rehabilitation schemes developed for Guernsey provide landing distances in both directions that are equal to the existing runway length (1,463 m). None provide the recommended length and width of RESA at both runway ends. Option C (Figure 2.1 ci-dessus) includes a 240 m long RESA at the west end, but at the minimum 90 m width and a RESA just short of 200 m at the east end.

Achieving the CAA’s recommended RESA length and width at both ends of the existing runway would result in the declared landing distances available being reduced from the present 1,458 m to 1,170 m, if contained between the east and west boundaries of the existing site, and reduced to 1,340 m, if contained within the site extended (as planned) to the west. Neither of these reduced landing lengths are acceptable for the continuance of existing commercial operations.

The provision of a starter strip over the downwind RESA would permit the take-off run and accelerate and stop distances to be increased by up to 200 m over the above landing distances, although the width of the site at the west end is constrained to the south (see Figure 2.1) and the taxiway to runway clearances limit the extent of taxiway at that end.

As the topography shows later in 3.5.4, extending the runway at the east end would be a substantial civil engineering project. Therefore it can be said that the provision of full length, full width conventional grass RESAs at Guernsey can only be achieved by an unacceptable reduction in declared runway distances (in relation to the needs of commercial air transport services operating into Guernsey), or by extending the runway platform at both ends at considerable cost.

Therefore the recommended 240 m long by 150m wide RESA cannot be reasonably achieved at both ends of the runway.

In Point b, the CAA accepts that an EMAS installation shall be based on the FAA requirements. As we explain later in section 3.7.2, the FAA have a “standard solution” and a sub-standard solution. The latter is only permitted if the former cannot be achieved. We understand from Point d, that the CAA will only accept the FAA’s standard EMAS solution. Otherwise declared distances may be adjusted to achieve the recommended RESA length.

The provision of a shortened EMAS enhanced overrun RESA may thus be acceptable to the CAA in this case. However, the required width of the overrun RESA and the dimensions of the undershoot RESA are not referred to in the CAA’s policy statement, are thus open to interpretation and are subject to the agreement of the CAA and the DCA.

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2.1.5 FAA

The US FAA depart from ICAO Annex 14 in some significant details of their equivalent regulation, which is Advisory Circular AC 150/5300-13. Relevant to this report are the fact that aircraft are classified differently, the safety zones around a runway are defined differently and some technical terms are different, or used with a different meaning.

The US also use imperial dimensions (but also quote rounded metric equivalents). These are generally, but not always, similar in magnitude to the dimensions used by ICAO.

Related issues are explained in more detail in section 3.2.3 below.

2.1.5.1 FAA EMAS Policy

The use of EMAS is explained in the FAA’s document AC 150/5300-13 and the FAA have also produced specific technical advice in AC 150/5220-22A in respect of the use of Engineered Materials Arresting Systems (EMAS) for Aircraft Overruns.

The relevant provisions of AC 150/5300-13 appear to permit an EMAS enhanced overrun RESA within a 180 m long overrun area as a straight alternative to a 300 m long overrun area. However, AC 150/5220-22A puts this option into the context of an airport where the provision of a standard overrun area is not practicable.

The FAA also has control over airport charges and a funding role in the USA. Specifically, Airport Improvement Projects, which are intended to improve operations, safety, security, or capacity, are considered on an individual basis for a possible FAA funded improvement grant, which can vary between 10% and 90% of the capital cost. This is determined by a cost benefit analysis to rules prescribed by the FAA. The present maximum grant at any airport is about 50 cents per outbound passenger. As with all Government funded capital works, the availability of grants is subject to availability of such funds within the overall FAA budget. Safety and security related projects tend to have high importance and also get a higher proportion of FAA funding.

Consequently, the FAA has produced specific rules in Order 5200.9 for the assessment of the potential benefits of EMAS as part of a RESA upgrade project. We must therefore be aware that such a funding arrangement may influence both the airports’ and the FAA’s decisions on the use of EMAS in the USA and may not be relevant elsewhere.

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3.1 Purpose of Runway End Safety Areas

Runway End Safety Areas are not provided for routine use by aircraft when landing or taking off from an airport. They are provided in recognition of the fact that aircraft can and do accidentally overrun or undershoot the ends of the runway. They are therefore designed as areas of cleared, graded and obstacle-free land that is able to support an aircraft and should minimise the extent of damage to the aircraft and minimise the degree of injury to its occupants in the event that an aircraft does overrun into or land short onto those areas.

Figure 3.1: Existing RESA East End Guernsey Airport Runway

Source: MM

The aviation industry generally seeks to minimise the risk of a potentially catastrophic accident to a probability of less than 1 in 10-7 (or 0.0000001), but this level of risk is not used to determine the shape and extent of the RESA.

Analysis of aviation accident data shows that the highest risk of accidents is around the extended runway centrelines at each end of the runway. This is in part because there is a concentration of aircraft movements at those points, but also because of the particular risks associated with those phases of flight. For this reason, various forms of safety zones are now provided at each runway end. Some extend a few hundred metres along and perpendicular to the runway centreline. Others extend several kilometres along and to each side of the runway centreline. Some zones are primarily designed to protect the aircraft and its occupants during normal operations or due to an accident, while others are intended to protect people on the ground.

3. RESA Requirements

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A RESA is just one of these safety areas. In considering its specific role of accommodating overruns on take-off or landing and undershoots on landing, landing-related overruns are generally about 5 times more likely to occur than take-off related overruns and all types of overruns are also about 4 times more likely to occur than undershoots.

There are also no stated risk levels in the ICAO SARPS associated with the minimum or recommended RESA provisions. It is understood that a RESA constructed to the full recommended dimensions should accommodate at least 90% of the overrun events and that a RESA constructed to the minimum permitted dimensions will only accommodate about half of those events (see also 3.6).

The above are very approximate figures for the risk rates derived from US and UK data by the FAA, NATS and others for a variety of aircraft types and runway conditions that do not all match those that apply at Guernsey Airport. We mention approximate statistics here and elsewhere in this report to give a sense of the magnitudes involved, but a detailed statistical analysis of the risks involved has not been undertaken and is not part of the scope of this report. Such a study may demonstrate that RESA dimensions that are less than the CAA’s recommended dimensions could be adequate for the nature of operations at this airport.

It also follows that overruns are more likely on runways where a high proportion of the movements require much, if not all of the available runway length to take-off or land. The risks in relation to commercial aircraft movements are therefore likely to be greater at Guernsey, with its 1,460 m long runway, than at (say) Heathrow which has two runways about 4,000 m long. That applies even though Heathrow has many more movements and many of those are by much larger aircraft than operate into Guernsey. This is because few of the runway movements at Heathrow actually need to utilise the full runway distances that are available.

At the other end of the scale, Guernsey has numerous movements by small general aviation aircraft (which are not permitted to operate into Heathrow). Many of these movements also do not require use of the full runway distances available at Guernsey and so the risk of overruns is also likely to be less for this category of aircraft than for larger commercial aircraft.

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3.1.1 Guernsey Runway Excursion History

As is stated later in 3.5.1, this is a factor to be considered when addressing RESA requirements.

The runway excursion history at Guernsey since 1999 (for commercial aircraft over 5,700kg MTOW) is:

1. 8 Aug 1999, Aurigny Shorts SD360: During landing roll on Rwy 09 aircraft veered sharply to the right, departed runway & struck PAPIs. Nose & landing gear damaged. No injury to 40 POB (excursion onto CGA, not overrun or undershoot RESA);

2. 21 Apr 2001, Aurigny Saab 340: During landing roll on Rwy 09 aircraft veered to the left, departed runway. No damage or injury to POB (excursion onto CGA, not overrun or undershoot RESA);

3. 8 Mar 2006, Emerald HS748: aircraft overran runway some 145m after landing on Rwy 27. Slight damage, no injury to 2 POB (excursion onto overrun RESA);

4. 17 May 2006, Club 328 Dornier 328 Jet: aircraft overran runway some 25m after landing on Rwy 09. Threshold light damage, no injury to POB (excursion onto overrun strip end zone);

In each of the above instances, the pilot was held principally to blame for the incident. All were landing related veer-offs or overshoots. No information has been provided on the extent of the lateral excursions.

The risk of undershoots is different. All aircraft follow the same approach paths and the approach lights and PAPI3 provide azimuth, horizon and vertical visual guidance to all pilots.

However, commercial aircraft also have the benefit of azimuth and vertical guidance from the Instrument Landing System (ILS) and are flown by commercial pilots who are generally more experienced. These factors reduce the risk of an undershoot by commercial aircraft, even in periods of low visibility.

_________________________

3 PAPI means a Precision Approach Path Indicator and is a system of four lights located to one side of the touchdown zone. Those light show two white aspects and two red aspects if the aircraft is on the correct glide path. They show three or even four white aspects if the aircraft is slightly or well above the glide path and they show three or even four red aspects if the aircraft is slightly or well below the glide path. It is a simple an effective device that can be used by all pilots providing the visibility

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The vertical angle of approach at Guernsey is the standard glide slope of 3 degrees to the horizontal. This is a shallow angle and means that a vertical variation of just 1m from the glide path could result in a 20 m horizontal variation in the point of touchdown.

The consequences of an accidental undershoot by a small general aviation aircraft can be just as severe for the aircraft itself and its occupants as for a commercial aircraft, but are usually less severe for others on the ground than an accident by a commercial aircraft, due to the latter’s greater mass and, in the case of a passenger aircraft, the concern is also for the greater number of souls on board.

In considering the appropriate RESA solution at Guernsey Airport, we have mostly been influenced by:

1. the risks particular to commercial aircraft;

2. the greater risk of overruns compared with undershoots; and

3. the need for adequate undershoot protection for all aircraft types.

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3.2 Runway Classification

The regulatory requirement to provide, and the respective dimensions of, Runway End Safety Areas are determined by the classification of the runway in question and so these are considered first.

3.2.1 ICAO

Runways are classified by a Code Number (1 to 4) and a Code Letter (A to F). The combination of these is used as a simple method to determine the relevant ICAO SARPs that apply. The Code Number is intended to reflect an aircraft’s runway performance characteristic and the Code Letter is related to their respective sizes.

The Code Number is determined by the longest Reference Field Length (RFL) of the aircraft types that the aerodrome intends to serve. The reference field length is the required runway length for take-off at a standardised set of operating conditions (e.g. maximum take-off weight, standard temperature, zero wind, at sea level). The determination of the aeroplane reference field length is solely for the selection of a code number and is not intended to influence the actual runway length provided.

This is because it is necessary to determine the length of the runway actually provided to also reflect its altitude, reference temperature and longitudinal gradient. An additional margin may also be provided to enhance safety, allow for exceptional weather, poor friction conditions and/or provide tolerance for future aircraft types. However, it is undesirable to provide a runway that is considerably longer than the adjusted length required for that category, as this may enable aircraft in a higher category to operate into an airport where the SARPs (which include safety clearances) are only applied for the lower stated category.

The reference field length for aircraft using Guernsey’s runway will generally be less than 1,800 m, which is classified as Code 3. However, if operating at below their maximum range, aircraft rarely need to take-off at their maximum permitted weight and thus can operate from a shorter runway. It is therefore possible that some of the smaller jet aircraft that could operate into Guernsey may have a RFL of more than 1,800 m, which would be classified by ICAO as Code 4. For example, the LR and AR versions of the Embraer EMB190 and EMB195 aircraft have RFL lengths in excess of 1,900 m.

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It is also of note, that ICAO classifies the runway Code Number by reference to take-off distances. However, that classification is then one of the main parameters used to determine runway dimensions and runway clearance characteristics for aircraft to land. The more onerous clearances are associated with landing runways rather than take-off runways and in particular instrument approach landing runways.

Anomalies can arise when applying the Annex 14 SARPs as a result of this underlying approach.

The Code Letter is usually determined by the largest wingspan of the aircraft types the aerodrome intends to serve (in a small number of instances it is determined by the overall width of the main undercarriage). This is a simple, but critical measure to ensure that runways and taxiways are wide enough and that objects are kept a safe distance clear of runway and taxiway centrelines and thus the wingtips of aircraft.

The divisions in the wingspan classification bands occur at 15 m, 24 m, 36 m, 52 m, 65 m and 80 m. The largest aircraft that Guernsey Airport intends to handle are those with a wingspan of up to 36 m (Code C). This category includes the larger turboprop aircraft such as the ATR and Dash 8 families, regional jets, including the Embraer E-jet range and the larger single-aisle (or narrow-body) jet aircraft such as the Airbus A320 and the Boeing B737 families. The only narrow-bodied aircraft with a wingspan greater than 36 m is the B757, which does not operate into Guernsey.

At present the runway at Guernsey is classified as a Code 3C runway.

It is also equipped with Category I precision instrument approach aids in both directions. This is also relevant in determining runway clearances and obstacle limitation surfaces on the approach.

If the runway were to be extended to (say) 1,700 m at some time in the future, it may remain Code 3 by the CAA classification, but is likely that the larger aircraft types would be Code 4 by the ICAO classification.

The relevant clearances on the ground are the same for Code 3 and Code 4 runways.

Therefore, even if a Code 4C runway classification were considered in planning current developments that are intended to safeguard for a runway extension, this should not be an onerous decision.

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3.2.2 CAA

The UK CAA determines the runway Code Letter as per ICAO. Until February 2001, the UK CAA also followed the ICAO definition for the Runway Code Number exactly as described above.

However, the CAA now determines the runway Code Number based on two of the actual declared take-off distances, TODA and ASDA. To explain this rule, it is necessary to explain that three take-off distances and one landing distance are declared for each runway in each direction of operations. These values may all be the same, or some or all may be different, depending on the precise runway arrangement and may be less than the overall length of the paved runway. The runway distances to be declared are:

TORA: Take Off Run Available (even when the take off run required equals, or is only slightly less than the distance available, safety margins mean that aircraft usually lift off about 2/3rds along this distance)

TODA: Take Off Distance Available (aircraft have to reach a height of 35 ft in this distance, even in the event of an engine failure just after take-off)

ASDA: Accelerate and Stop Distance (distance aircraft have to accelerate, abandon the take-off and come to an emergency stop on the runway)

LDA: Landing Distance Available

Understanding how these respective distances apply can be complex. The simplest case is where the entire length of the paved runway is used for both landing and take-off in each direction. The start and end points of TORA, ASDA and LDA thus coincide with the ends of the paved runway and all the declared distances equal the length of the runway (TODA may still be more, as this can include an area beyond the end of TORA that is clear to fly over at very low altitude). Any blast pads provided at the runway ends are to prevent erosion of the soil by prop wash or jet blast and not measured as part of the runway length.

However, in each direction, none of the above declared distances have to end at the same point along a runway and the take-off and landing distances may also start at different points. Each value is then different and this can lead to complex shapes for clearances and safety zones.

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The CAA method of classification is to determine the Code Number depending on the greater value of TODA and ASDA. In practise, this is very onerous for several regional airports that serve commercial air transport operations in the UK that, at present, are classified as Code 2 even though they have take-off distances of between 1,300 and 1,400 m, but are unable to provide the much greater clearances required for Code 3 (and Code 4) runways. Future development at those airports should be in compliance with the latest regulations, but that will not be practical or affordable in many instances.

As far as we are aware, the CAA are unique in taking this approach, which makes no allowance for any increases in runway length required for a given category of aircraft due to altitude, temperature or gradient.

Runways are designated (or “named”) by the magnetic compass bearing of the direction of the approach (rounded to the nearest 10 degrees). The runway at Guernsey Airport is designated Runway 09 (eastbound) and Runway 27 (westbound). We use these references in this report.

The paved runway is 1463 m long with the addition of a 59 m long blast protection pad at the east end.

At present (as of 11th March 2010), the declared runway distances at Guernsey Airport are:

For Runway 09, TORA = 1,463 m, TODA = 1,601 m, ASDA = 1,463 m and LDA = 1,458 m

For Runway 27, TORA = 1,462 m, TODA = 1,639 m, ASDA = 1,462 m and LDA = 1,458 m

Thus, the primary classification of Guernsey’s runway is not affected by the CAA’s different approach to classification and remains a Code 3C runway by the CAA method.

In addition, for many years the CAA has also recognised a “lower third” Code 3 sub-category and the runway at Guernsey airport may have fallen into this sub-category in the past. This has been affected by the revised definition, which now applies to runways with TODA and ASDA distances of up to 1,500m. While the longest ASDA is 1,463 m, the longest TODA at Guernsey is 1,639 m and so the runway is not in this sub-category under the present rules. This sub-category only affects a small number of provisions and in addition, they are not be important in this study.

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3.2.3 FAA

In AC 150/5300-13, the FAA classifies the size of aircraft in the same six wingspan bands as ICAO (Code A to F), but refers to these as Airplane Design Groups (ADG) and assigns these with Roman numerals (I to VI). Thus Group I is equivalent4 to Code A, Group III is equivalent to Code C and Group VI is equivalent to Code F.

The FAA do not classify runways by the reference field length, nor the actual runway length, but by an aircraft approach speed category. The FAA designate their approach speed categories by the letters A to E, which has the obvious potential to be confusing in this report.

Table 3.1: FAA Aircraft Approach Speed Category

Approach Category Minimum Speed Maximum Speed

Category A - 90 knots

Category B 91 knots 120 knots

Category C 121 knots 140 knots

Category D 141 knots 165 knots

Category E 165 knots -

Again, as far as we are aware the FAA are unique in using this method of runway classification.

In considering the aircraft types in operation at Guernsey, turbo props such as the Dash 8 Q400 are classified by the FAA method as having an Airport Reference Code (ARC) of A-III and the ATR 72 as B-III. Jets such as the Avro RJ/BAe 146 are classified as B-III, A318 as C-III, Citation V as B-II, Citation VI as C-II and CRJ-200 as C-II. Embraer do not publish on their website the approach speed of their E-Jet range of aircraft, which vary by weight. These types may be expected to have approach speeds between 91 knots and 140 knots and will be considered as Category C-III for the purposes of this report.

Existing operations at Guernsey may mean that the runway presently only serves up to category B-III aircraft, but operations by some of the larger executive jets and the re-introduction of jet services are likely to take operations into the FAA’s C-III category for its Airport Reference Code.

We use this category, when establishing FAA requirements.

_________________________

4 the FAA also consider tailfin height in these classifications

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3.3 Runway Width

The minimum width for a Code 3C (and FAA ARC C-III) precision Instrument approach runway is 30 m. The runway width at Guernsey is 45 m. This is to provide greater lateral tolerance for landings in conditions of high cross-winds, which occur frequently at this location.

The minimum width for a Code 4C runway is 45 m, so this width would also be suitable in the event that the runway is extended in the future.

It should be noted that the width of any part of a Code 3C runway that is solely intended for take-off can be reduced to 30 m (or even 20 m for the first 150 m of the take-off run).

3.4 Runway Strip Requirements

A runway is to be surrounded by a rectangular runway strip. Its purpose is to:

a. reduce the risk of damage to an aeroplane running off the runway by providing a graded area which meets specified longitudinal and transverse slopes, and bearing strength requirements; and

b. protect aeroplanes flying over it during landing, balked landing or take-off by providing an area which is cleared of obstacles except permitted aids to air navigation.

Figure 3.2: Landing Runway Strip

150m

150m

300m

Source: Based on CAP 168

For a Code 3C precision instrument approach runway, the recommended strip is 300 m wide overall5 and extends 60m before the start of the LDA and 60 m beyond the end of the LDA.

_________________________

5 Where overall widths are stated, they are symmetrically disposed about the runway centreline.

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Figure 3.3: Take-off Runway Strip

75

m7

5m 1

50

m


For any part of a Code 3 runway that extends outside this area and is solely intended for take-off, the minimum strip width is 150 m (or less at the very start of the take-off run) and extends 60m beyond the end of the longer of TORA or ASDA.

The 60 m length of strip at the runway ends needs to be taken into account when considering any RESA arrangement or comparing these with FAA dimensions. For example, the total overrun distance from the end of the landing distance to the end of the RESA is the length of the RESA plus 60 m.

These same RESA dimensions apply to a Code 4C runway in the event that that the runway is extended in the future and has to be reclassified.

The FAA requirements are somewhat different. Among other surfaces, the runway is surrounded by an Object Free Area (OFA) and a Runway Safety Area (RSA).

Figure 3.4: FAA Areas

120m

120

m

240

m

150

m

Source: Based on AC 150/5300-13

The Runway Object Free Area is the largest of these. It is a rectangular area extending 1,000 ft (300 m) beyond the runway end with an overall width of 800 ft (240 m). The OFA may be considered the nearest equivalent of the ICAO runway strip.

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3.4.1 Cleared and Graded Area

Figure 3.5: Cleared and Graded Area

210

m

300m

150

150


Within a runway strip is a cleared and graded area (CGA).

The minimum recommended width of the area that should be cleared and graded to allow for the safe ground running of an aeroplane that has left the runway is 210 m overall for a Code 3C precision instrument runway, but that may be reduced to an overall width of 150 m over a distance of 150 m from each end of the landing runway. The width of the CGA gradually increases over the next 150 m to the 210 m width.

At each runway where operations occur in both directions (the normal situation) an envelope of the combined take-off and landing Runway Strips and CGAs is produced and as a minimum, these areas must meet the stated obstacle, profile and surface treatment requirements.

The FAA requirements are again somewhat different (see Figure 3.4 above). The runway is surrounded by a rectangular “Runway Safety Area” (RSA), which may be considered the equivalent of a combined CGA and RESA.

For an ARC of C-III, the length prior to the landing threshold is 600 ft (180 m)6 and the length beyond the runway end is 1,000 ft (300 m). Its overall width7 is 500 ft (150 m).

In addition, the FAA RSA standards cannot be modified or waived like other airport design standards. The dimensional standards remain in effect regardless of the presence of natural or man-made objects or surface conditions that might create a hazard to aircraft that leave the runway surface.

_________________________

6 If vertical guidance is provided

7 Where overall widths are stated, they are symmetrically disposed about the runway centreline.

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3.5 RESA Requirements

For a Code 3 precision instrument approach runway, ICAO and the CAA require RESAs for each direction of operations extending before and after both ends of the runway strip that encompasses the LDA and after the end of the runway strip that encompasses the take-off runway.

No RESA is required before the start of a take-off run, but a clearance is normally required behind an aircraft to provide protection from prop wash or jet blast.

ICAO/CAA RESAs have specific obstacle, profile and surface treatment requirements that are not all the same as those for the CGA.

As stated above, the FAA has no separate RESA requirement, but AC 150/5300-13 can be interpreted as including this area within the ends of its “Runway Safety Area” (RSA). Different undershoot and overrun lengths can apply in the FAA’s regulations.

3.5.1 RESA Length

The minimum RESA length shall be 90 m, but the recommended minimum length is 240 m for Code 3 and Code 4 runways. It is noted that recommended minimum RESA length is 120 m for either a Code 1 or a Code 2 instrument runway. This is a simplified response to the lower aircraft masses and thus reduced inertias and likely overrun distances of the Code 1 or Code 2 aircraft types.

The CAA lists factors to be considered when determining the length of RESA to be provided:

a. the nature and location of any hazard beyond the runway end;

b. the type of aircraft and level of traffic at the aerodrome and actual or proposed changes to either;

c. aerodrome overrun history;

d. overrun causal factors;

e. friction and drainage characteristics of the runway;

f. navigation aids available;

g. scope for procedural risk mitigation measures; and

h. the net overall effect on safety of any proposed changes, including reduction of Declared Distances.

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These are to be reviewed annually.

The implied RESA lengths in the FAA RSA dimensions are 240 m for an overrun RESA and 120 m for an undershoot RESA (where vertical approach guidance is provided).

3.5.2 RESA Width

The minimum ICAO/CAA RESA width shall be twice the runway width. The runway width at Guernsey is 45 m, so the minimum width is 90 m.

The recommended minimum RESA width is the same as that for the cleared and graded area. If the CGA is reduced at the ends as described in 3.4.1, for a Code 3 or Code 4 runway, this is 150 m overall.

The width of the FAA RSA is 150 m throughout.

The Pavement Rehabilitation project at Guernsey is only proposing to provide RESAs to the minimum 90 m width. This width will capture the majority of overrun and undershoot events. However, the reports we have read do not provide any evidence or analysis to explain why a RESA constructed to the minimum width provides an adequate level of protection.

The selection seems to have been influenced by a desire to achieve the longest rectangular shape at the west end, rather than on a risk basis.

If a conventional grass RESA is installed to the minimum 90 m width, then the cleared and graded area available for aircraft to traverse will reduce in overall width from 150 m to 90 m at a point 60 m beyond the furthest of the ends of the TORA, ASDA or LDA distances in question.

We are of the opinion that the width of the runway CGA and the RESA should not instantaneously reduce in the general direction of aircraft travel. To do so may result in an instantaneous change from a safe overrun area to a hazardous overrun area and/or risk striking an obstacle square on. If the width of the CGA and RESA gradually reduces (as the CGA is permitted to do between its 210 m and 150 m overall widths), then the pilot will be directed back towards the safer CGA or RESA surface, or if unable to steer the aircraft, it will meet the boundary at a shallow angle, which may result in a less severe impact.

Where space is limited, it would be safer to commence 150 m wide at the end of the CGA, keep it as wide as practicable and gradually reduce the RESA width to no less than 90 m.

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3.5.3 RESA Gradients

The overall longitudinal slope and the transverse slopes in a RESA should not exceed a downward slope of 5% (1:20). There are no regulatory requirements to avoid rapid changes in slope in the RESA, nor at its boundary, but we would wish to see gradual changes of slope to minimise the degree of potential damage to an overrunning aircraft and injury to its occupants.

For comparison, the longitudinal slope on a runway strip CGA should not exceed 1.5% (1:66) on a Code 4 runway and 1.5% (1:66) on a Code 3 runway and the transverse slopes on either should not exceed 2.5% (1:40).

The longitudinal slope on a runway should not exceed 1.25% (1:80) on a Code 4 runway and 1.75% (1:57) on a Code 3 runway, but in either case, should not exceed 0.8% on the first and last quarters of the runway. The transverse slopes should be downward and not exceed 1.5% (1:66) each side of the runway centreline. The existing slopes on the runway at Guernsey airport do not comply with these requirements, and are being addressed by the Pavement Rehabilitation project.

The different slope limits for RESA, CGA and the runway itself are significant to the volume of the earthworks that would be required to extend the runway platform at Guernsey Airport at the west end, as the ground profile will depend on the intended use of those sections of the runway platform.

It is therefore significant if the intention is to safeguard for a future extension to the runway over those same areas. The ground may need to be profiled for its long-term use and that may require an additional volume of earthworks

The ILS localiser aerial array must also be constructed at a suitable height.

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3.5.4 Existing RESAs at Guernsey Airport

Figure 3.6: Existing RESA at West End

Source: Google Earth Pro

The overall length of the paved runway is 1,463 m. The undershoot RESA at the west end (to Runway 09) is 120 m long (+ 60 m strip = 180 m from threshold). The width over much of the length of the area is approximately 110 m. The RESA gently rises in the centre, then gently slopes down to the west. Note location of the (red) ILS localiser aerial array in this and the next figure.

Figure 3.7: Land to West of West End of Runway

Source: MM

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An overrun or undershoot west of this RESA would be hazardous for the aircraft and its occupants. At present, the land beyond the runway at the west end also drops down away from the runway, but in this case it falls across a field before reaching a narrow public road (La Mare Rd).

The distance from the Runway 09 threshold to the public road along the extended runway centreline is about 260 m, which is less than the CAA’s recommended 300 m distance to the first obstacle (which would normally be the ILS Localiser aerial array.

Figure 3.8: Existing RESA at East End

Source: Google Earth Pro

The undershoot RESA at the east end (to Runway 27) is approximately 83 m long (+ 60 m strip = 143 m from threshold, which is inset 5m from the pavement end). The overall width of the area is at least 150 m and more unobstructed land exists at least a further 50 m to both the north and south of this area. The ground slopes gently down to the east.

To provide the CAA’s minimum 90 m long RESA at this end, the end of the runway would need to be inset some 13 m. The Airport has informed us that this has been considered, but the threshold marking and the declared distances are presently based on a point inset 5 m from the east end of the paved runway. If adopted the LDA would reduce to 1450 m, as would the Rwy 09 TORA and ASDA.

The ILS Localiser aerial array at the east end of the RESA is at the top of an embankment which drops down some 3 m onto a narrow public

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road (La Villiaze Road). The land then falls away at an increasingly steep slope towards the east.

Figure 3.9: Public Road across East End of Runway

Source: MM

Figure 3.10: Land Sloping Down to East at East End of Runway

Source: MM

The pylon structures in Figure 3.10 support the approach lights and show the line of the extended runway centreline. An overrun or undershoot into this area would be extremely hazardous for the aircraft, its and the dwelling occupants and any road users present at the time.

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3.5.5 Overrun Role of a RESA

Although a rare event, there are numerous reasons why an aircraft may overrun the runway length available on take-off. Errors in pre-flight payload, fuel weight and runway distance calculations, throttle and other power-related settings, significant adverse meteorological conditions and engine failure at a critical stage are probably the most common causes. If an engine fails after a pre-determined critical speed is reached (known as V1), the pilot in charge should continue to take-off and the clearances provided around a runway allow for the reduced climb performance of the aircraft in flight beyond that point. If the aircraft does not continue to take-off beyond V1, it must brake to a halt. The ASDA should be sufficient for the aircraft to stop. However, any delay in aborting the take-off or technical failure may mean that the aircraft will not be able to stop on the runway before the end of this distance. For some aircraft, the ASD required is significantly less than that available, which reduces this risk. At Guernsey, this would only apply to small general aviation aircraft. Commercial aircraft will often be operating with a required accelerate and stop distance that is close to, or even equal to, the ASD available.

Several of the reasons that might cause an overrun on take-off will not prevent the pilot from retaining control of the aircraft’s direction on the ground. However, a burst tyre or engine failure prior to lift-off may cause the aircraft to veer off to one or other side of the runway, although this would occur well before the end of the runway. If the pilot abandons the take-off near to V1 and applies full emergency brakes, there is a heightened risk that a tyre may burst, or the brakes may fail on one side, leading to a loss of directional control. This may result in the aircraft veering outside the runway edge prior or after reaching the runway end. If an aircraft veers of the runway and the forces on the nose wheel are excessive, then it may break off, again removing directional control. Nosegear failure has happened on a number of occasions during an overrun onto a grass RESA elsewhere. The probability of such events influences the required RESA width.

Several potential reasons as to why an aircraft may overrun the runway length available on landing are similar to those on take-off. Errors in flight payload, fuel weight and landing distance calculations, flap, reverse thrust and other brake-related settings or equipment failure and adverse meteorological conditions are also among the potential causes. However, aircraft on approach have a much greater ability to depart from their assumed track, due to meteorological conditions, systems failure or pilot misjudgement. That may lead to an approach either above or below the glideslope (as well as to either side).

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If the aircraft lands beyond the touchdown point, the distance available to brake to a stop (or exit taxi-ing speed) is reduced. This scenario is one of the more common events and is often associated with strong wind conditions, including wind shear and these in turn may be associated with heavy rain and a wet runway.

Some of the reasons that might cause an overshoot on landing may also prevent the pilot from having control of the aircraft’s direction on the ground. These include water or slush on the runway, a burst tyre, an asymmetrical failure of the braking system. However, in most cases the pilot will retain directional control after touch down.

Directional control is important when considering potential pilot actions in an overshoot scenario. No pilot will steer head-on into a solid obstacle, or over the top edge of a steep drop in the ground level, if they have any choice in the matter. Pilots will try and miss a very hazardous object and may attempt a ground loop to avoid this. Thus aircraft may deliberately veer off to one side or the other in an overshoot event on a conventional RESA. Pilot action in the presence of an EMAS enhanced RESA is the reverse. The desired action is to steer into the EMAS bed. This is discussed further in section 3.7.

3.5.6 Undershoot Role of a RESA

An approach below the glideslope may lead to an aircraft landing short. This may still be on the runway, because the touch down zone is approximately 300m beyond the start of the runway landing distance (known as the threshold) to provide such tolerance. In some instances the threshold may also be inset from the end of the paved runway surface. However, any landing prior to the start of the pavement would be onto the runway strip or the undershoot RESA. Such a landing may be “soft” or “hard”. In the latter case, this can result in damage to the aircraft’s tyres, the undercarriage, or other systems associated with decelerating the aircraft (such as the automatic deployment of lift spoilers and the application of reverse thrust – which have been known to result in a consequent overshoot) and such an impact can also result in loss of directional control.

Engine failure on approach can also lead to landing well short of the runway, but such instances can occur at any point during this phase of flight and while the point of touchdown can be influenced by pilot actions, such events may be outside anyone’s control. If a positive climb rate cannot be established in time, engine failure may result in a catastrophic crash landing with the resultant loss of the aircraft, crew and any passengers and may also cause fatalities on the ground.

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The length of RESA provided can never protect against all such potential accidents. However, it follows that the longer the RESA provided, the greater the tolerance to accommodate undershoot events.

Statistically, undershoots only occur at about one quarter the frequency of overrun events.

3.6 ACRP Report 3

The US Transportation Research Board’s Airport Cooperative Research Program is sponsored by the FAA and Report 3 (published in 2008) is their Analysis of Aircraft Overruns and Undershoots for Runway Safety Areas.

The report makes clear that there are a number of limitations in the data used to help formulate its conclusions. Notably the position an aircraft came to a halt and the circumstances surrounding the event are not always recorded in a manner that is useful for this research. There are also many events that are not reported because there were no consequences, but which would otherwise help establish a truer picture of the probability of an event and the degree that an aircraft undershoots its touchdown point, or the extent it overruns its intended landing or take-off distance. Information on the lateral position of the aircraft was not always recorded either. Another aspect is that the landing or take-off lengths required were not recorded to enable any comparisons to be made or any patterns to be established with the respective distances that were available.

Events involving helicopters, light aircraft, training, armed services, single engined, or piston engined aircraft, those that resulted in veer-offs or accidents more than 600m from the runway ends were all excluded from this study’s results. This improves its relevance to commercial operations and runway end events.

However, the authors still identified a total of 459 events to analyse. Most occurred in the US. Of the 459 events, 93 were undershoots on landing (0 in the UK), 274 were overruns on landing (24 in the UK), and 92 were overruns on take-off (5 in the UK). Analysis was broken down by accident and incident.

The data was also “normalised” to a level runway at sea level, ISA conditions, level terrain and an infinitely long hard runway.

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Of particular interest were the probable scatter of undershoot and overshoots relative to the runway ends and the respective patterns of lateral distance from the runway centreline.

Figure 3.11: Normalized Distances Model for Landing Undershoots

Source: US Transportation Research Board

NB 1000 ft ≈ 300 m, 2000 ft ≈ 600 m, 4000 ft ≈ 1200 m

Undershoots were about 20% of the sample Approximately 60% occurred within 180m, 72% occurred within 300m

Figure 3.12: Normalized Lateral Distances Model for Landing Undershoots


NB 200 ft ≈ 60 m, 400 ft ≈ 120 m, 600 ft ≈ 180 m

Approximately 80% occurred within 45m, 88% occurred within 75m

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Figure 3.13: Normalized Distances Model for Landing Overruns


NB 1000 ft ≈ 300 m, 2000 ft ≈ 600 m, 4000 ft ≈ 1200 m

Landing overruns were about 60% of the sample Approximately 60% occurred within 180m, 75% occurred within 300m

Figure 3.14: Normalized Lateral Distances Model for Landing Overruns


NB 500 ft ≈ 150 m, 1000 ft ≈ 300 m, 1500 ft ≈ 450 m

Approximately 75% occurred within 45m, 88% occurred within 75m.

The study only identified a low level of correlation between the longitudinal and lateral position of the events. Consequently, the study concluded that the transverse location distribution of undershoot accidents is fairly constant along the longitudinal locations from the threshold.

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Figure 3.15: Normalized Distances Model for Takeoff Overruns


NB 1000 ft ≈ 300 m, 2000 ft ≈ 600 m, 4000 ft ≈ 1200 m

Takeoff overruns were about 20% of the sample Approximately 45% occurred within 180m, 60% occurred within 300m

Figure 3.16: Normalized Lateral Distances Model for Takeoff Overruns


NB 500 ft ≈ 150 m, 1000 ft ≈ 300 m, 1500 ft ≈ 450 m

Approximately 70% occurred within 45m, 85% occurred within 75m

The report does not attempt to correlate events to aircraft type or size.

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Specific studies for the probability of incidents or accidents within RESAs at other airports follow this general pattern, with a substantial majority of events occurring within the minimum areas, but with a significant proportion occurring outside these areas.

In 2008, the Airport commissioned NATS to consider the public safety zones (PSZs) that are relevant to Guernsey Airport. The risk of an undershoot or overrun at Guernsey within the RESA area could be produced as a sub-set of those calculations and would be more specific to the local operating conditions. It should also relate longitudinal and lateral events.

3.7 EMAS Enhanced RESA

As we have stated earlier, at some airports it is impractical, or prohibitively expensive, to provide the land necessary for the provision of a RESA to the full recommended length and width. While reducing the declared landing and take-off distances would enable the recommended RESA dimensions to be provided, in many instances that would prevent some existing and often commercially important aircraft operations from continuing to take place.

Thus, various methods have been devised to provide an aircraft arrestor system that can reliably and safely decelerate an overrunning aircraft in a shorter distance. This has included a prepared soft ground area, or a lightweight aggregate bed, but the stopping performance of the former is not very predictable or reliable and the latter is not safe in the event of a fire, particularly if spilt fuel flows into the aggregate bed. Both methods also prevent rescue vehicles getting close to the aircraft.

The RESA surface is normally grass and this too may not provide a reliably predictable rate of deceleration, particularly if the grass is wet and/or the ground surface has become softened by the weather. In the United States, the FAA only refers to their requirements of the ground in their Runway Safety Area in dry conditions. They make no requirements for its performance in the wet.

Consequently, an aerated soft concrete product has been developed in the United States that will reliably and predictably crush under the pressure of the tyres from an overrunning aircraft. This energy absorbing material increases the drag on the undercarriage and is designed to achieve a rate of deceleration of about 1g (about 10 m/s2) in a fairly controlled manner and to do so with minimum damage to the aircraft itself.

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Figure 3.17: Contained Overrun at Yeager Airport, Charleston, West Virginia

Source: Zodiac Aerospace

This is known as an Engineered Material Arresting System (EMAS). Its development and testing has been overseen by the FAA and the research programmes and actual aircraft overruns have demonstrated its effectiveness in arresting aircraft overruns. It has therefore been accepted for use by the FAA (subject to technical and financial criteria) as a means of improving the runway safety area (RSA) where a standard FAA overrun area within their RSA is difficult to provide.

To date, the Zodiac ESCO EMAS has been installed at 51 runways in over 30 commercial US airports and there are 2 installations at airports in Spain and China. Apart from development testing, there have been 7 overrun incidents in which all the aircraft in question were stopped within the arrestor bed, preventing significant injury to passengers or significant damage to the aircraft.

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3.7.1 EMAS Construction

EMAS is constructed of a cellular concrete material that is manufactured as numerous precast blocks of defined strength and dimensions. These are laid on a paved area. About 30% are bonded to the pavement. The height of the blocks varies, to provide a shallow entry ramp and get deeper the greater the distance into the bed. The sides and far end are also ramped to facilitate access by emergency vehicles and egress by passengers. The top and side surfaces are sealed.

Figure 3.18: EMAS Bed Construction at Barajas Airport, Madrid

Source: MM

The following figures diagrammatically indicate the plan shape and cross sections of an EMAS installation.

In the FAA’s “standard” EMAS design, the Runway Safety Area Length is at least 180 m. The set back must be sufficient to avoid jet blast damage from aircraft departing in the opposite direction.

The base surface is designed to support the weight of an aircraft, but as with runway shoulders and blast pads, on the basis of infrequent use. Part of the set-back area will also need to be paved as a blast pad. If the set-back distance is greater than that, we are of the opinion that the entire set-back area between the runway end and the start of the EMAS

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bed should be paved in this way and none of the intervening distance left as grass. Otherwise the risk of damaging an overrunning aircraft (or undershooting aircraft in the reverse direction) is high for a relatively small cost saving. Zodiac, the manufacturers are of the same opinion.

Figure 3.19: Plan Indicating EMAS Layout


Figure 3.20: Diagram of Longitudinal Long Section


Figure 3.21: Diagram of Cross Section


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3.7.2 Basis of EMAS Design

In their Advisory Circular AC 150/5220-22A, the FAA quote data gathered for aircraft overruns over a 12 year period (1975 to 1887) which showed that 90% of overruns exited the runway end at speeds of 70 knots or less and that most come to rest between the extended runway edges within 1,000 ft (300 m) of the runway end.

This influences the runway exit speed selected and the length and width of the EMAS bed design proposed in most locations.

Figure 3.22: Theory of EMAS Bed Action Figure 3.23: Result of EMAS Bed Action

Source: Zodiac Aerospace Source: Zodiac Aerospace

The length of the EMAS bed is determined by the manufacturer based on the 70 knot runway exit speed, the distance between the end of the runway and the start of the EMAS bed, the slope of the site and the specific list aircraft types expected to be in operation and significant to the detail design of the bed. The design method has been developed mathematically and verified in tests under the supervision of the FAA. The manufacturer claims to use more than 100 variables in their computer program that calculates the design of the EMAS bed and the predicted performance for each aircraft type. The CAA has accepted that methodology. We have no reason to question the basis on which the design has been developed and the length of bed specifically proposed for use at Guernsey in terms of its overrun performance.

The FAA’s requirement for a conventional overrun area within their RSA extends 1,000 ft (300 m) beyond the runway end (equivalent to a 240 m long RESA). The FAA’s standard design for an EMAS enhanced overrun RSA extends 180 m beyond the runway end (equivalent to a 120 m long RESA). In addition, the FAA recognises that even this shortened dimension may not be possible at some airports.

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Having examined the spatial constraints at Guernsey Airport, we neither consider it impractical nor unaffordable to provide a RESA that is at least 120 m long (i.e. extending 180 m from the end of the runway). The FAA standard design should therefore be used for any EMAS installation.

The remaining issues of concern are the width of the EMAS bed compared with the potential path of some overrunning aircraft and the fact that a shortened EMAS enhanced RESA offers no additional or equivalent undershoot protection.

In the specific case of the width issue, the statement by the FAA quoted at the start of this section clearly implies that an EMAS bed equal in width to the runway should be encountered by about 90% of overrunning aircraft. This is a higher percentage than implied by ACRP Report 3, but is the basis on which the FAA have given their approval.

Most past events are where there was no arrestor bed. In some instances the pilot in charge may have deliberately chosen to steer off of the runway centreline to try and avoid obstacles, but if an EMAS bed is provided, pilots would now endeavour to steer into the arrestor bed. Therefore, in order to maximise the use of an EMAS arrestor bed in an overrun event, pilots must be aware of its presence at the end(s) of the runway, a fact which should be promulgated in the airports entry in the CAA Aeronautical Information Publication (AIP) and commercial equivalents. They must also have directional control, which will apply in the vast majority of cases, but not all overrun events.

At Guernsey, it would be possible to provide RESAs with an overall width of at least 90 m and in several of the runway development scenarios considered, the full recommended overall width of 150 m may be achievable. However, although a wider EMAS bed could be provided at additional cost, we have not encountered any examples and are assuming that the width of any EMAS bed provided at Guernsey remains the same as the width of the runway (i.e. 45 m).

The RESA must be wider than the 45 m EMAS bed width to provide an overrun area for aircraft that undershoot, or veer off and overrun into the area outside of the extended runway edge lines. The FAA standard design for an EMAS enhanced RSA, still assumes an overall RSA width of 150 m, which is the same as the ICAO/CAA recommended width for a Code 3 or Code 4 RESA. We support the concept with a 150 m RESA width. If that width cannot be provided due to site constraints, then the 90 m minimum should apply, but in our opinion, without any instant change from the 150 m wide CGA to the reduced RESA width.

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3.7.3 Design Aircraft for EMAS Bed

The EMAS manufacturer calculates the dimensions they recommend for the EMAS bed based on the particular mix of aircraft that are expected to operate using a computer-based analysis that they have developed. This is required by the FAA to consider multiple aircraft parameters, including, but not limited to allowable aircraft undercarriage gear loads, undercarriage configuration, tyre pressure, aircraft centre of gravity, aircraft speed and allowable g-forces on the aircraft occupants.

While the largest or heaviest aircraft may be the critical aircraft for design purposes, that is not always the case. The undercarriage configuration varies between some aircraft types and that may result in different degrees of drag. Lighter aircraft may also prove a critical case, if there is a risk that they might not bed into the EMAS material.

DRB Associates, the manufacturer’s UK representative has stated that the aircraft types considered for the overrun design at Guernsey were:

Embraer E195,

L188 Electra,

Bombardier Dash 8 Q400,

ATR 72,

Cessna Citation and

Jetstream 32

3.7.4 Performance of Overrun EMAS Bed

The performance of the latest design of EMAS does not materially change between dry and wet conditions or if overlain by snow. The manufacturers state that their latest design is also now less susceptible to jet blast erosion and they claim it requires less routine maintenance.

An overrun into an EMAS bed is a more predictable event than an aircraft overrunning onto a grassed RESA, even if that is built to the recommended dimensions. The extent of aircraft damage and injury to its occupants is also much lower than on a graded overrun area in all the actual incidents to date (although the number so far, 7, is small).

Because it is designed to limit the stress applied to the undercarriage, a low level of damage is to be expected and is a benefit of the concept.

Based on the evidence presented and the experience of actual events to date, Mott MacDonald is satisfied that an overrunning aircraft entering into an EMAS bed (within its design parameters) will be brought to a controlled stop with minimum injury to its occupants and minimum damage to the aircraft itself.

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3.7.5 Equivalent RESA Length

The CAA’s RESA requirements are based on, and the same as, the ICAO SARPs, even though the method of runway classification is different. To retain/maximise declared distances, the CAA’s policy is also to require an EMAS installation to be equivalent to a 240 m long RESA (+ 60 m strip).

There are no stated performance standards for a conventional (grass) RESA and ICAO/CAA make no distinction between its overrun and undershoot roles. In addition, for a given runway Code Number, its dimensions are not varied in relation to the actual length of the runway, the size of the aircraft types it is intended to serve, or their respective numbers of movements.

In Halcrow’s 2009 Report8, they consider the respective risks of an overrun into various lengths of RESA. They start by assuming that a 240 m long RESA has an overrun risk of 1 x 10-7 per movement on the basis that this meets the CAA’s risk criteria. They go on to apportion risk levels for shorter RESA lengths. They do not state the related RESA width, but we would assume from the basis of the selection of this figure that the recommended width of 150 m also applies. However, none of the schemes hitherto considered propose to provide this RESA width.

In our opinion, the level of risk of an overrun at Guernsey airport relates to all the relevant factors at Guernsey Airport and there is therefore no strong reason to assume that an overrun risk of 1 x 10-7 applies to a 240 m long by 150 m wide RESA at Guernsey.

As described in 3.5.1, the CAA requires a minimum RESA length of 90 m for a Code 3 or Code 4 runway and a Code 1 or Code 2 instrument approach runway. The CAA also recommends a minimum length of 120 m for a Code 1 or Code 2 instrument approach runway and a minimum length of 240 m for a Code 3 or Code 4 runway.

Interestingly, the reference to instrument approaches makes that a determining parameter for Code 1 and Code 2 runways, although the guidance provided on approach is better. This is the opposite of the FAA approach. In addition, the size related Code Letter classification does not play any part in determining RESA dimensions.

_________________________

8 Clause 8.2.6

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There is a very loose connection between the respective aircraft sizes and the various runways classifications. Under CAP 168, a Code 4 runway is any runway with an ASDA or TODA of 1,800 m or more. A Code 4 classification applies to all the runways at major international airports, such as Heathrow, which handle a mix of short, medium and long-haul narrow-bodied and wide bodied aircraft, often handling aircraft up to the Code F Airbus A380 in size.

Thus the same recommended 240 m length and 150 m width applies for a RESA at the ends of the Code 3 runway at Guernsey as at Code 4 airports as diverse as Southend, East Midlands, Aberdeen or Heathrow. A calculated risk assessment may be a more appropriate method to use to determine appropriate RESA dimensions.

The manufacturer of EMAS calculates the required material strength and the EMAS bed dimensions based on the actual range of aircraft intended to be handled. The risk of an event occurring plays no part in the design of an EMAS installation, which is about stopping the design aircraft. This is a more refined approach and the resulting performance of the EMAS is predictable, whereas that of a grassed RESA is not.

There is therefore no simple relationship between the dimensions of conventional grass RESAs and an “equivalent” EMAS enhanced RESA.

In its Advisory Circular 150/5220-22A (dated 30/09/2005), the FAA does refer to a standard EMAS design that provides a level of safety that is “generally equivalent” to a full RSA built to the FAA’s standard dimensions in dry conditions, which are 1,000 ft (300 m) long, measured from the end of the relevant runway declared distance, by 500 ft (150 m) wide.

This FAA “standard” EMAS installation provides an EMAS bed that finishes 600 ft (180 m) from the end of the relevant runway declared distance. However, the length of the EMAS bed (and hence the length of set back distance between the end of the runway distance and the start of the EMAS bed) is not prescribed, but varies according to the deceleration characteristics of the relevant design aircraft. Appendix 2 of Advisory Circular 150/5220-22A contains graphs relating speed and EMAS length for 7 specific aircraft types. These all assume no operating reverse thrust and poor aircraft braking performance.

We conclude that the FAA’s standard EMAS installation is the closest that can be achieved to meeting the CAA’s equivalency test.

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3.7.6 Undershoot Scenario

The FAA requirement is that an undershoot, in which an aircraft touches down on an EMAS bed, must not cause control problems for the aircraft. The Zodiac EMAS design meets this requirement.

An undershoot onto an EMAS bed is expected to cause shallow wheel ruts in surface once the undercarriage (which initially is at full extension) makes contact with the upper surface of the EMAS blocks.

3.7.7 Light Aircraft

Light general aviation aircraft tyres may not penetrate into the bed to a significant extent to provide the full drag effect. However, the overrun distance provided by a standard FAA EMAS installation is the same as that recommended by the CAA for a Code 1 or Code 2 runway RESA.

3.7.8 Impact of Vehicles on EMAS

The strength of the EMAS bed is sufficient to support vehicles with high-floatation tyres, although they may cause shallow wheel ruts. Vehicles should only run over the EMAS bed in an emergency.

3.7.9 Maintenance and Service Life

An EMAS bed does require occasional inspection and maintenance. Joints may need to be sealed. The strength of the aerated concrete blocks must also be checked regularly (probably every 5 years)

The FAA’s financial rules require the calculation for the lifetime cost of an EMAS bed to be on the basis that it is replaced after 10 years. This is a cautious approach built into their financial cost/benefit model and does not necessarily mean that the beds will have to be replaced after 10 years.

In fact, the FAA’s requirement is that an EMAS installation should have a service life of twenty years. Existing installations are only just exceeding 10 years old and so this lifespan is yet to be proven, but the condition of the existing beds does not yet suggest that this lifespan will not be achieved.

The only EMAS replacements to date have been in connection with runway development options, although we understand that some of the early installations that were constructed close to the runway end suffered some jet blast and vibration damage.

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3.7.10 EMAS Damage and Repair

The EMAS installation must be designed and constructed so that it will not be damaged by jet blast or propwash. We understand that the latest Zodiac EMAS design, which has a plastic top coating and the minimum set-back distance meet this requirement.

The damage to the EMAS bed caused by actual overruns is extensive in the aircraft’s wheel tracks, but unless caused by emergency or recovery vehicles, is unaffected elsewhere. Concerns have been expressed as to the cost and time that will be taken to effect a repair. The costs should be reclaimable from the aircraft’s operators and their insurers. Pilots will be notified by NOTAM of a damaged EMAS installation.

The EMAS bed is a means of mitigating the potential damage of an accident. Unless there is a contributory cause that would equally apply to other aircraft immediately using the runway, then the probability of a repeat event in the near future is very low. The bed also remains effective unless another overrunning aircraft follows the same wheel tracks (again very unlikely).

The FAA’s specification requires that a damaged EMAS is repaired in a timely manner and must be designed to be repairable within 45 days.

We accept the FAA’s specification as appropriate and adequate and the CAA’s policy is to follow the FAA’s recommendations.

3.7.10.1 Impact on ILS Localiser Signal

Assuming an aircraft overruns heavily into the EMAS, but stops, as it should, before the ILS aerials, then once removed and the wheel tracks cleared, this will leave longitudinal grooves in the formerly smooth top surface of the EMAS bed, which is immediately in front of the ILS localiser aerial array. The array has a significant overall width. It does not use the ground to create the signal, but the ground does have the potential to adversely affect the signal. In the overrun events to date, no problems with localiser signals have been reported. We therefore consider it unlikely to cause a problem. However, a specialist such as NATS could model this scenario to establish if the wheel ruts might cause any deterioration in the accuracy of the localiser signal.

A temporary filling to the wheel ruts may also mitigate against this if it were anticipated to be a problem.

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The ILS Field Monitor aerial will be within the EMAS bed, on the centreline and at about 75m before the localiser. That places it near the start of the EMAS bed. It is therefore vulnerable to being hit during an overrun, but no more so than without an EMAS bed and can be replaced independently of any EMAS repair.

3.7.10.2 Replacement Blocks

Zodiac is a US based company and it may take addition time to manufacture and deliver replacement blocks to Guernsey compared with many US sites. It is not clear if that could be reliably achieved within 45 days.

The estimate for Option A (with EMAS) includes for an entire spare set of blocks to be purchased and stored on site. We consider that an excessive requirement. However, having considered all of the above, at this stage, we accept that there may be a case to stock 20% of one set of blocks to facilitate a quicker repair.

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4.1 Pavement Rehabilitation Options

Numerous options considered in the development of the Rehabilitation project. Several of these have been put forward in the various reports to the States and three Options have remained under consideration:

1. Option A (with EMAS) within the existing site boundary;

2. Option C (grass RESA) extended site to the west – requires additional land;

3. Option C1 (grass RESA) extended site to the west – within land acquired to date.

Several of the other Options, including Options B and D were rejected for not providing an adequate improvement to the RESAs.

Figure 4.1: Diagrams of Pavement Rehabilitation Options

Source: Guernsey Airport

4. Runway Development Options

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4.2 Option A (with EMAS)

The overall width of the existing site (between the localiser aerial bases) is 1778 m.

Providing the recommended 300 m long (240 m RESA + 60 m strip) overrun and undershoot area at each end of the runway would result in an LDA of 1178 m, which is not acceptable and would cause a cessation of many commercial services.

Providing the FAA EMAS enhanced 180 m long overrun area and the FAA undershoot area at each end of the runway (which is equivalent to 120 m RESA + 60 m strip) would result in an LDA of 1418 m, which is also not acceptable.

The maximum evenly distributed overrun and undershoot RESA length that could be achieved within the existing site is 97.5m at each end, which is barely more than the absolute minimum and results in a reduction in the existing RESA length at the west end.

We therefore consider below the two versions of the EMAS enhanced RESA options that have been proposed and a third that is compliant with the FAA & CAA’s requirements.

4.2.1 Supplier’s EMAS RESA Proposal

The US supplier (ESCO) has made the following specific proposal in relation to the provision of an EMAS enhanced RESA at both ends of the Guernsey Airport Runway:

Figure 4.2: Proposed Preliminary Design for Guernsey Airport

Source: DRB Associates

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It is a preliminary design for the EMAS system and consists of an EMAS with a total length of 340.2 ft (103.45 m), including back steps, and a nominal width of 170.1 ft (51.85 m), including two columns of side steps on each side and in the rear. The system starts 35ft (10.66 m) from runway end. The total length is 375.2 ft (118.9 m) including the rear access track.

Pavement underlying the EMAS is required to be crowned for drainage and they recommend that the pavement is 200 ft wide overall so as to provide 15 ft wide areas on each side of the arrestor bed in order to support airfield vehicle traffic. Pavement strength within the minimum paved area must be sufficient to support the occasional crossing of the design aircraft (similar to the shoulder strength pavement, i.e. 10 aircraft passes/year without deformation).

By referring to a 35 ft set-back dimension, we are assuming that this is the minimum length required. As will be seen from the following figure, this does not utilise the full length of RESA available, particularly at the west end. Moving the beds to the outer end of the available RESA lengths would not materially alter the proposal.

Figure 4.3: Existing Runway with Proposed EMAS Installations at Each End


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4.2.2 RPS Option A (with EMAS)

The recommended location for an EMAS bed is at the far end of the overrun area. This is to minimise the extent of any incursions and thus limit the damage to the EMAS bed so caused and this location also reduces the probability and extent to which an undershoot makes contact with the EMAS bed.

The design by RPS followed this recommendation and in addition approximately equalised the RESA lengths by displacing the runway 24 m to the west, resulting in a RESA length of about 90m at each end.

We have compared this proposal with each of the CAA’s requirements and its newly stated policy on the use of EMAS:

The dimensions do not meet the FAA’s EMAS standard design recommendations;

The dimensions do not meet the FAA’s RSA width requirement;

The dimensions only meet the CAA’s minimum RESA requirements;

The improvements provide protection of overrunning aircraft entering into the EMAS bed, which is the most probable scenario, but do not enhance protection either side of the EMAS bed, or enhance protection for those that undershoot the runway;

The dimensions do not meet the CAA’s policy for EMAS provision without causing a reduction in declared distances; and

The dimensions do not meet the CAA’s RESA width recommendations.

In addition, RPS took the view that the EMAS bed needed to be laid on a nominally flat pavement. However, Zodiac, the designers and manufacturers have supplied bed length calculations for a number of scenarios including for a bed that slopes down away from the runway end. This would reduce the required volume of earthworks for this option.

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4.3 Standard FAA EMAS Proposal

While we are prepared to accept that the EMAS bed dimensions proposed by Zodiac will stop an overrunning aircraft that exits the runway at 70 knots or less and enters into the EMAS bed, that is not the entire extent of the RESA requirement. As discussed earlier in this report, in improving the RESA provision, the intention is to protect a wider range of potential events due to overruns and undershoots.

The following layout is based on the concept of providing an FAA “standard” EMAS enhanced RESA at each end of a 1,463 m long LDA. The FAA standard version being a 45 m wide EMAS bed located at the outer ends of a 180 m long x 150 m wide overrun area (the length being equivalent to a 120 m long RESA + 60 m runway strip end area):

The runway has been relocated by first placing the east end of the “standard” 180 m long EMAS bed just short of the ILS localiser Aerial Array at the east end of the site. A runway, equal in length to the existing runway is then provided to the west and a second 180 m long EMAS enhanced RESA added at the west end. This 1,823 m overall length ends up just short of the first road (La Mare Road).

Figure 4.4: 1463m long Runway with 180m long EMAS Overrun Areas


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Because the EMAS bed is set back 100m from the runway end, we estimate the length required to be about 70m.

We understand that there are arguments against closing La Mare Road.

Figure 4.5: Standard FAA RESA at West End


With this Option, it looks possible to retain La Mare Road, although the development would be very close to it and requires the RESA to slope down towards it. This option displaces the runway 42m to the west. That dimension is less than for several of the other options and in consequence, it may be possible to retain the existing Taxiway Bravo.

Such a modified EMAS enhanced proposal does extend the site to the west beyond its existing boundary. However:

This provides a 120 m long x 150 m wide RESA at both ends

The dimensions comply with the FAA’s EMAS standard design;

The dimensions comply with the CAA’s EMAS policy;

The width complies with the FAA’s and CAA’s requirements;

The improvements provide protection of overrunning aircraft entering into the EMAS bed, which is the most probable scenario, enhance protection either side of the EMAS bed and enhance protection for those that undershoot the runway; and

The dimensions comply with the FAA’s undershoot area.

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4.3.1 Cost

We have compared this option with the construction requirements and cost (May 2010 budget) for Option C.

We have deducted the entire cost of the western extension of the runway, including the RESA-related earthworks, but retained all other items in Option C. This amounts to approximately £9m (incl prelims).

We have then added:

At the west end, a 42m long runway extension, the blast pad and EMAS pavement extending to 180 m from the new runway end, a 70m long EMAS bed, drainage and RESA-related earthworks; and

At the east end, the EMAS pavement extending 80 m beyond the existing blast pad, a 70m long EMAS bed and drainage

Our estimated cost for these works is £15m (including prelims). That is an additional cost of approximately £6m on the cost of Option C.

If required, the cost of 20% spare blocks is estimated as £0.7m

4.3.2 Further EMAS Options

Any long term extension of the runway would need to take place at both the east and west ends and only about 70% of the EMAS blocks would be reusable.

However, because the RESA length is the least, this concept minimises the extent to which a runway extension to any length over 1650 m needs to extend the runway platform to the east.

The RESA can be moved about 120m more to the west at a 150 m width (as per our option C2). Alternatively, with a RESA that tapers down to 90 m wide at the Ruette de la Tourelle end (as per our modified Option C), it could be moved about 190 m west. All the respective declared distances could then be increased by these same amounts. I.e. the LDA could be increased to about 1580 m or to about 1650 m respectively. In the longest case, achieving a 1700m LDA would require a 60 m extension of the runway platform to the east.

The latter is probably the most practical solution for achieving a 1700 m long runway.

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4.4 Option C (Grass RESA)

Option C is the preferred option that stems from of the previous studies. It provides a 240 m long by 90 m wide RESA at the west end and a 197 m long by 90 m wide RESA at the east end. It is acceptable, but the RESAs should be wider.

4.5 230 + 200 RESA Proposal

The following layout is based on Option C. It is intended to be the same except that it provides a tapered RESA approximately 230 m long and up to 150 m wide at the west end and a 200 m long by 150 m wide RESA at the east end.

Our figures are sketches. Option C achieves a 240 m long x 90 m wide RESA at the west end and a 197 m RESA at the east end. These slightly longer dimensions have been produced using a CAD base and should be considered more accurate.

It is apparent that the emphasis to date has been on improving RESA length, but the CAA also recommends a wider RESA and the FAA requirements are also for wider undershoot and overrun areas.

Figure 4.6: 1463m long Runway with 230m and 200m long RESAs


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Figure 4.7: Tapered RESA at West End


This option is to show that wider conventional RESAs are achievable at both runway ends with the minimum of modification. Indeed a detail design may show that the RESA at the west end could be more than 230 m and possibly the full 240 length, but we have chosen to take a more cautious approach at this stage.

The runway is displaced about 125 m to the west, but remains within the existing site. The land required to the west for the RESA extends up to the second road (Rouette de la Tourelle).

4.5.1 Cost

We have added the additional width of RESA earthworks at the west end of the runway and assumed all other costs as per Option C. The resulting estimate is that this amendment would add about £0.5m to the price for Option C.

4.5.2 Further Options

The RESA lengths could be equalised at each end, but the bias in the direction of operations is to the west, the case for this is not strong.

A hybrid could be developed from this and the previous option. It would provide a full length 240 m long tapered RESA at the west end and an EMAS enhanced RESA at the east end. This would permit the declared distances to be increased by a small amount (about 40 m).

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4.6 Option C2

Option C1 is a derivative of Option C that improves the undershoot and overrun RESA length at the west end, but only improves the overrun RESA at the east end.

Having rejected Option A (with EMAS) because the RESA improvements are insufficient, it would be inconsistent to accept the very short (78m) undershoot RESA to Runway 27 provided by this proposal. That is regrettable, because in a number of other respects it offers benefits over Option C.

However, having concluded that a 120m long undershoot RESA would be acceptable with a standard FAA EMAS installation in paragraph 4.3, that would also be the case if a 240m long grass overrun RESA were provided. To minimise the land take required, this can be achieved in both directions by insetting the thresholds 120m.

Option C2 has therefore been developed as a compliant version of Option C1.

Figure 4.8: Option C2 with 120m Undershoot RESAs and 240m Overrun RESAs at Each End


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Figure 4.9: West End Option C2


4.6.1 Cost

We have added the additional 45 m length of runway at the west end and assumed all other costs as per Option C.

We estimate that this Option would add about £1.5m to the price for Option C.

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Airports should still seek to provide the recommended RESA lengths and widths

The use of an EMAS enhanced RESA on a restricted site is now permitted by the new CAA policy and could be used at Guernsey

The FAA standard EMAS installation fulfils the CAA requirements, but in most cases, the FAA’s shorter undershoot RESA must be accepted to retain declared distances

Operational advantages of an EMAS enhanced RESA:

Provides a predictable and reliable method of bringing an overrunning aircraft to a halt;

Performance only relies on limited braking action by the aircraft and does not rely on the frictional characteristics of ground;

Performance not affected by rain or snow;

For a given set of circumstances, will arrest an aircraft in a significantly shorter distance than a grass or surfaced RESA;

Does minimal damage to the aircraft and minimises potential injury to aircraft occupants; and

Can be walked on and run on if necessary by emergency response vehicles (some damage to EMAS blocks will occur)

Operational disadvantages of an EMAS enhanced RESA:

Relies on the aircraft entering the EMAS bed to stop the aircraft, which means pilot must have control of aircraft direction, understand the need to steer onto the bed and have confidence that it will stop his aircraft;

Is limited in width (usually only installed to the same width as the runway), thus providing no overrun protection for an aircraft that has veered off the runway to either side;

Provides no benefit in an undershoot scenario and if installed as part of a reduced length and/or width of RESA, will mean there is a reduced degree of undershoot protection;

Is damaged by the overrunning aircraft and is more complex, time-consuming and costly to repair than a grass RESA;

Requires occasional maintenance; and

May have a limited life (presently assumed to be 20 years)

5. MM Conclusions re EMAS RESA

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In the context of its use at Guernsey, the proposed length of the RESAs in Option A (with EMAS) does not meet the FAA’s, nor the CAA’s requirements.

The provision of the FAA standard installation, which has CAA approval, would still require the runway platform to be extended to the west beyond the existing site boundary.

In this case, 150m wide RESAs are possible at both ends.

The option that provides a 180m long undershoot/overrun area (120m RESA) at each end will just fit between La Mare Road and the eastern boundary providing the RESA is graded down toward the road, but offers no simple means to extend the runway in the future.

Costs of an EMAS enhanced RESA

There will be specific costs associated with the supply and installation of an EMAS RESA at a particular airport. These may be more or less than the costs of providing a conventional grass RESA, depending on the dimensions of both, the quantity and type of earthworks involved, the cost of land and the respective ongoing maintenance costs.

In general, there is neither an economic case for or against the use of an EMAS enhanced RESA. The main reason for considering an EMAS installation is that the provision of the required RESA at any particular location is considered impractical or prohibitively expensive. As soon as a particular installation is examined, the project specific costs can then be established and a cost /benefit analysis undertaken.

However, there may be other reasons, such as locally heightened risks of overruns, environmental impacts or difficulties with land acquisition that may make the use of an EMAS enhanced RESA preferable to the required conventional RESA, regardless of its relative cost.

As we have seen in Section 4, the additional capital cost at Guernsey is about £6m over Option C, plus the possible addition of £0.7m to provide a stock 20% of the blocks for a single bed to facilitate a quicker repair. The EMAS solution will also have some ongoing block storage and maintenance costs. The benefit is the provision of wider RESAs with an overrun performance approximately equivalent to 240m long RESAs at both ends and the extension of the airport site to the west is reduced.

Its selection depends on the perceived benefits of the reduced site area and its performance compared with the additional costs.

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