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Section/division Occurrence Investigation Form Number: CA 12-12a

AIRCRAFT ACCIDENT REPORT AND EXECUTIVE SUMMARY

Reference: CA18/2/3/8965

Aircraft Registration ZS-PXL Date of Accident 20 September 2011 Time of Accident 1204Z

Type of Aircraft Robinson R44 (helicopter) Type of Operation Commercial Flight-Game or Livestock Culling

Pilot-in-command Licence Type Commercial Age 31 Licence Valid Yes

Pilot -in -command Flying Experience

Total Flying Hours

1808.3 Hours on Type 760.0

Last point of departure Graspan National Park – Northern Cape Province

Next point of intended landing Graspan National Park – Northern Cape Province

Location of the accident site with reference t o easily defined geographical points (GPS readings if possible)

Open field at Graspan National Park

Meteorological Information

Wind direction: Westerly, Temperature: 27˚C, Cloud Cover/Base: Nil Visibility: >5000 m.

Number of people on board 1 + 1 No. of people injured 0 No. of people killed 0

Synopsis

The pilot accompanied by a passenger – veterinarian flew the RH44 helicopter on a commercial game or livestock cull flight at Graspan National Park. The pilot reported that he suddenly felt a severe vibration accompanied by a grinding/growling noise from the helicopter. The pilot decided to execute an emergency landing in an open field. A hard landing followed during the emergency landing. In the process of the landing the main rotor blades struck the tail boom and severed it. The helicopter sustained substantial damage in the impact sequence. The pilot and passenger survived the occurrence without sustaining injury.

Probable Cause

Mechanical failure experienced during flight resulting in emergency landing followed by hard landing. Contributory Factors: Forward flex plate failed due to fatigue crack developing at bolt hole underneath the bonded washer. Fatigue crack on forward flex plate not detected during maintenance inspection. Aircraft Maintenance Manual (AMM) limits flex plate crack detection to visual inspection.

IARC Date Release Date

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Section/division Occurrence Investigation Form Number: CA 12-12a Telephone number: 011-545-1000 E-mail address of originator: [email protected]

AIRCRAFT ACCIDENT REPORT

Name of Owner/Operator : Kriek Helicopters (Pty) Ltd trading as Kriek Helicopters Manufacturer : Robinson Helicopter Company Model : RH44 Nationality : South African Registration Marks : ZS-PXL Place : Graspan National Park – Northern Cape Province Date : 20 September 2011 Time : 1240Z All times given in this report are Co-ordinated Universal Time (UTC) and will be denoted by (Z). South African Standard Time is UTC plus 2 hours. Purpose of the Investigation : In terms of Regulation 12.03.1 of the Civil Aviation Regulations (1997) this report was compiled in the interest of the promotion of aviation safety and the reduction of the risk of aviation accidents or incidents and not to establish legal liability . Disclaimer: This report is given without prejudice to the rights of the CAA, which are reserved.

1. FACTUAL INFORMATION 1.1 History of Flight 1.1.1 The pilot flew the RH44 helicopter on a commercial game or livestock cull flight for

South African National Parks (SANParks) at Graspan National Park. The pilot was accompanied by a passenger - veterinarian on board the helicopter. The intention of the flight was to dart some animals - buffalos which belongs to SANParks. The pilot reported that after they darted a few of the buffalos, the helicopter suddenly developed a vibration which was accompanied with a grinding/growling noise. The helicopter was flying at an altitude of approximately 20 feet (7 meters) above ground level (AGL) at the time.

1.1.2 According to the pilot, the time when he felt the vibration and heard the grinding/growling noise, the helicopter immediately swayed over approximately 60 degrees to its left side. In the process of it swaying to the left, a loss of power was experienced followed by audible warning signalling low RPM condition. The helicopter then started to vibrate severely and lost height. The pilot applied collective control just before touchdown to cushion the landing. During the landing sequence the helicopter landed hard. The left side skid got stuck in soft soil and it felt as though the helicopter could roll over. The pilot applied aft cyclic control to stop the helicopter’s roll movement. The pilot heard a loud bang noise coming from the rear side of the helicopter. The evidence shows that the main rotor blades struck the tail boom. The aircraft violently swung over to the left side which stopped when the pilot closed the engine throttle. The aircraft settled on the ground and the pilot shut it down completely.

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1.1.3 The pilot and passenger evacuated from the aircraft without sustaining any injuries. The aircraft sustained substantial damage during the impact sequence.

1.2 Injuries to Persons

Injuries Pilot Crew Pass. Other Fatal - - - - Serious - - - - Minor - - - - None 1 1 - -

1.3 Damage to Aircraft 1.3.1 The aircraft sustained substantial damage.

Figure 1, shows the damage caused to the aircraft.

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1.4 Other Damage 1.4.1 None. 1.5 Personnel Information

Nationality South African Gender Male Age 31 Licence Number 0271037632 Licence Type Commercial Licence valid Yes Type Endorsed Yes

Ratings Test Pilot – Class 2, Night, Flight Tests – Single Engine Piston, Cull Ratings.

Medical Expiry Date 30 September 2012 Restrictions None Previous Accidents None

Flying Experience:

Total Hours 1808.3 Total Past 90 Days 78.7 Total on Type Past 90 Days 78.7 Total on Type 760.0

1.5.1 There was no anomaly identified with the pilot in this regard.

1.6 Aircraft Information

Airframe: Type Robinson R44 II Serial Number 11828 Manufacturer Robinson Helicopter Company Date of Manufacture 2007 Total Airframe Hours (At time of Accident) 1003.7 Last MPI (Date & Hours) 16 September 2011 999.8 Hours since Last MPI 3.9

C of A (Issue Date) (Expiry Date) 03 September 2007 02 September 2012

C of R (Issue Date) (Present owner) 17 August 2007 (Kriek Helicopters) Operating Categories Standard – Part 127

Engine : Type Lycoming IO-540-AE1A5 Serial Number L32037-48E Hours since New 1003.7 Hours since Overhaul TBO not reached.

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Main and Tail Rotors:

Main Rotor Blades:

Part No: C016-5

Installation – 21 April 2008 @ 116.6 hours

Serial No: 5124 Serial No: 5046

Tail Rotor Blades:

Part No A029-2

Installation – 7 June 2007 (new)

Serial No: 5247 Serial No: 5242

Total Time:

Tail Rotor - 1003.7 & Main Rotor (blades) – 887.1

1.6.1 The RH44 helicopter was imported to the Republic of South Africa (RSA) as a new

product from United States of America (USA). After arriving in the country, the helicopter was assembled and then registered on the civil aircraft register. The SACAA then carried out a certificate of airworthiness (CoA) issuance inspection on the helicopter and approved it for use on special operation - game or livestock cull. The RH44 helicopter was used on special operations from June 2007 to date.

1.6.2 All the aircraft documentation (certificate of registration, certificate of airworthiness, and certificate of release to service etc.) found carried on board the helicopter was valid and in compliance with applicable regulation.

1.6.3 Maintenance Performed: The helicopter was maintained by an approved aircraft maintenance organisation (AMO). The type of maintenance carried out by the AMO on the helicopter was mandatory periodic inspections (MPI) which took place annually or after every 100 hours flight time. After the MPI′s were completed, the helicopter had a performance test flight and it was then certified airworthy.

1.6.4 The aircraft maintenance documentation was reviewed during the investigation:

(i) Logbooks: The entries of maintenance activities that were carried out on the helicopter was appropriately recorded and certified in the logbooks in compliance with applicable regulations. There was no anomaly identified with the maintenance information recorded in the logbooks.

(ii) Flight Folio: The flight folio did not have any open or deferred defects.

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1.6.5 According to the Airframe Logbook, the following maintenance was carried out on

the helicopter from 22 August 2007 to 16 September 2011.

Inspection Total Airframe Hours

Date

Defects found and rectified

MPI 4.3 22 August 2007 None

MPI 99.8 7 March 2008 None

MPI 197.2 23 July 2008 The v-belts were adjusted for 60 second engagement time. Fan shaft bearing greased with G28

MPI 297.1 22 November 2008 Upper and lower actuator bearing greased with G28

MPI 357.7 26 March 2009 None

MPI 395.8 24 April 2009 None

MPI 495.2 7 July 2009 None

MPI 597.2 22 January 2010 Upper and lower actuator bearing greased with G28

MPI 660.2 29 April 2010 None

MPI 693.4 21 May 2010 None

MPI 793.2 13 September 2010 The forward flex plate stack up was incorrect. Rectified - stack up corrected.

MPI 894.8 22 May 2011 Upper and lower actuator bearing greased with G28

MPI 999.8 16 September 2011 Original clutch actuator refitted. Fan scroll bracket repaired. Spray clutch rear oil seal replaced.

1.6.6 The evidence show that after the above maintenance were completed by the AMO,

the helicopter was certified as being airworthy and released to service. The helicopter performance was satisfactorily and it was in a serviceable condition.

1.6.7 Parts Failure: During the wreckage investigation, the evidence found shows that a

mechanical failure had occurred during the flight. It was discovered that the forward intermediate flex plate (forward end of tail rotor driveshaft) with identifying markings: A947-2G, batch number: Lot 292, having inspection stamp: RHC 28 USA which connect the engine output to the tail rotor transmission input within the drive train had failed.

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Figure 2, shows location of flex plate that failed.

Figure 3 & 4, shows flex plate that failed.

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1.6.8 Below find copy of Robinson Illustrated Parts Catalog showing the location where the flex plate (item 17) is installed on the tail rotor drive shaft.

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Figure 5, shows the tail rotor drive shaft installation.

1.6.8 During the onsite investigation, the evidence found showed that the forward flex plate was severely deformed during the failure. The flex plate had fractured adjacent to one of the four fixing holes. The tail rotor drive shaft end had separated from the flex plate.

1.6.9 According to Robinson Helicopter Company, Aircraft Maintenance Manual (AMM), Section 7, Part 7.320 – Tail Rotor Drive Shaft Installation, the following is required:

(i) Support drive shaft through upper aft tail cone inspection hole to

prevent damage and for alignment purpose.

Caution : Improper installation of the flex plate can damage the tail rotor drive shaft and gearbox.

1.6.10 According to Robinson Helicopter Company, Aircraft Maintenance Manual (AMM), Section 7, and Part 7.220 – Clutch Assembly Installation, the following is required:

(i) Item 7, install intermediate flex plate per Section 7.330.

Note: Section 7.330, reinstall the flex plate using the shims, torque the attached bolts per Section 1.320, install palnut and torque stripe.

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Figure 6, shows forward and intermediate flex plate installation. 1.6.11 According to Robinson Helicopter Company, Aircraft Maintenance Manual (AMM),

Section 2, and Part 2.410 – Inspection Procedure and Checklist, the following inspection on the intermediate flex plate and forward end of tail rotor drive shaft is required during maintenance:

(i) Inspect intermediate flex plate for cracks and fretting. (See figure below)

(ii) The inspection procedure stipulated above is carried out during annual maintenance, at every 100 hour interval of operation. These are all visual inspections on the flex plate.

1.6.12 Fuel Status: The helicopter had total of 170 Litres fuel on board before take-off. The

helicopter flew for approximately 0.5 hours from 13:25 to 14:55 on the day. The fuel remaining at the time of the accident was 140 Litres. The helicopter had sufficient quantity of fuel on board for the intended flight.

1.7 Meteorological Information 1.7.1 The meteorological information taken from the pilot questionnaires.

Wind direction Westerly Wind speed 5 to 8 kts Visibility >5000 m Temperature 27˚C Cloud cover Nil Cloud base Nil Dew point unknown

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1.8 Aids to Navigation 1.8.1 The helicopter was fitted with standard navigation equipment which was approved

for the type. Other additional navigation equipment found installed was included on the approved equipment list. The pilot did not report any defect or malfunction experienced with the navigation equipment. The navigation equipment was serviceable.

1.9 Communications. 1.9.1 The helicopter was operated in uncontrolled airspace at Graspan National Park in

Northern Cape Province. The pilot transmit his intentions on the VHF radio frequency 124.8 MHz.

1.9.2 The helicopter was fitted with King KY 196 A type VHF transmitter equipment. The

pilot did not report any defect or malfunction experienced with the communication equipment. The communication equipment was serviceable.

1.10 Aerodrome Information 1.10.1 The location where the helicopter operated was in an open field away from an

aerodrome. 1.11 Flight Recorders 1.11.1 There was no flight recorder (Flight Data Recorder and Cockpit Voice Recorder)

installed, neither was it required by regulations. 1.12 Wreckage and Impact Information 1.12.1 Impact Information: The helicopter was flying at low altitude, approximately 20 feet

above ground level (AGL) at Graspan National Park. The pilot experienced a mechanical failure, resulting in an emergency landing being executed. The helicopter landed very hard on its landing gear (skids) during the emergency landing. The left side skid then got stuck in the soil and started to roll over to its left side. The pilot attempted to correct the roll movement, but he was unsuccessful because the main rotor then struck the tail boom. The tail boom was severed in two halves and the one piece separated from the helicopter. The helicopter then settled on the ground on its landing gear (skids).

1.12.2 Wreckage: The wreckage was examined and it was determined that damage was

caused to the tail boom structure, tail rotor drive train, landing gear (skids) and main rotor blades. The conclusion was that the helicopter had sustained substantial damage.

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1.13 Medical and Pathological Information 1.13.1 The pilot had a valid Class 1 aviation medical certificate with no waivers. The pilot

had no medical condition which may have prevented him from flying the aircraft. 1.13.2 The pilot and passenger did not sustain any injury in the accident. 1.14 Fire 1.14.1 There was no evidence of pre or post impact fire. 1.15 Survival Aspects 1.15.1 The accident was considered to be survivable. The cockpit and cabin area of the

helicopter was still intact after being involved in the accident.

1.15.2 The pilot and passenger were properly restrained with the safety belts and safety harnesses of the helicopter. They evacuated from the helicopter safely without sustaining any injury.

1.15.3 The pilot and passenger transmitted on the radio and received assistance from SANParks ground personnel (people collecting the darted animals) after the helicopter was involved in the accident.

1.16 Tests and Research 1.16.1 Intermediate Flex plate: The flex plate was removed from the wreckage and taken

for metallurgical examination. The metallurgical report concluded the following:

(i) The flex plate had been severely deformed during the failure.

(ii) The flex plate fractured adjacent to one of the four fixing holes.

(iii) No metallurgical or material defect or deficiency was found which have caused initiation.

(iv) The origin of the fracture was a small thumb-nail shape crack showing clear

indications and features typical of fatigue which initiated underneath the reinforcing washer.

(v) The surface of the initial crack was discoloured, indicating that it had been

present for a significant period of time.

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(vi) The four threaded fasteners were also examined. It was observed that no fretting was present on the shank surface, indicating that the fasteners were correctly tightened and had not been moving relative to the plate.

Figure 4 & 5, shows fractured flex plate lug and thumb-nail fracture concealed underneath the reinforcing washer.

Figure 6, shows the four threaded fasteners. 1.16.3 Robinson Helicopter RH44 Maintenance Manual requires that the tail rotor drive

shaft should be supported when conducting tail rotor drive shaft installation and/or removal. A survey was carried out amongst the South African approved Robinson Helicopter Aircraft Maintenance Organisations (AMO’s), to determine what maintenance procedure they use to support the tail rotor drive shaft during installation and/or removal. The evidence found shows that each AMO were using their own developed different method to support the tail rotor drive shaft. The manufacturer did not give a detailed explanation of the method how to achieve the support. The maintenance process is being interpreted in different ways by the AMO’s using different specially developed procedures as a means of compliance.

1.16.3 Robinson Helicopters (R22 & R44) accident history involving flex plate failures that

occurred in South Africa:

(i) Accident number: CA18/2/3/8777, Robinson R22 Beta, ZS-SCS on 10 April 2010, Training Flight at Cape Town International Aerodrome. The probable

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cause of the accident was determined to be the forward flex plate that fractured after liftoff and resulted in tail rotor drive shaft failure.

(ii) Accident number: CA18/2/3/8902, Robinson R44 Ravin II, ZS-RVA on 25 February 2011, Aerial Survey at Paardevlei. Metallurgical examination revealed that the fractured surface showed signs of fatigue from the hole underneath the washer contact surface. The probable cause of the accident was determined to be Uncontrollability of the helicopter after the failure of flex plate on the forward flex coupling.

1.16.4 Safety recommendations that came forth out of the above identified accidents were

the following:

(i) Ground all South African registered Robinson R44 and R22 helicopters pending a proper inspection of the flex plate before any further flight.

(ii) The SACAA Airworthiness Department to compile an inspection procedure/ method to carry out the inspection of the flex plate. (Both recommendations were approved by DCA on 18 March 2011 but no implem entation to date)

1.17 Organizational and Management Information 1.17.1 Operator: The Operator had a valid Air Service license issued by South Africa Air

Service Licensing Council. The operator was authorised to operate the types: G3 and G10 air services and category: H2 of aircraft.

1.17.2 The operator also had a valid Part 127, Air Operating Certificate (AOC). The AOC

was issued on 28 January 2011 with expiry date of 30 January 2011. The aircraft registration, ZS-PXL was approved on the AOC for utilization.

1.17.3 According to the Operations Specification: The Operator was approved to perform

the following types of air services.

(i) G3 – Aerial Patrol, Observation and Surveying. (ii) G10 – Game and Livestock selection, culling, counting and herding. (iii) N1 – transport of passengers.

1.17.4 The Operator conducted the above identified operations from their main base at

Barkley West District in the Northern Cape Province. 1.17.5 Robinson Helicopter Corporation: The metallurgical report with the information of

flex plate failure was forwarded to the State of Design and Manufacture. The response received back was the following:

“After reviewing the reports on the flex plates with our engineering department, our initial thoughts are that the failures are due to a maintenance issue and not a strength or durability issue.

The crack appears to have initiated at the edge of the washer. If the driveshaft is allowed to move beyond its normal range of motion (up & down, left & right), the flex

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plates will of course exceed their intended range of motion and the area near the inboard edge of the washer is where the most stress is going to develop.

The maintenance manuals instruct the maintenance personnel to support the driveshaft whenever the actuator is disconnected or removed. If the shaft is allowed to drop or is raised excessively, the forward or intermediate flex plate could be damaged.

I would be interested in knowing if any maintenance had been performed in these areas (clutch replacement, V-belt replacement, actuator repair, fan shaft removed, etc.) on these two aircraft and if so, how was the shaft supported. The maintenance performed on September 16 could be suspect. The shaft would have needed to be supported the entire time the clutch actuator was out for repair or service, especially if the helicopter is being moved around the hanger or ramp.

One of the reports mentions five other reports of flex plate failure. We have seen failures relating to fretting due to lack of torque on the hardware and the crack initiates at the bolt hole, but we are unaware of any other flex plate failures in this manner. Is it possible to obtain details of these other reports to verify the similarities?”

1.17.6 Aircraft Maintenance Organisation: The helicopter was maintained by an approved

aircraft maintenance organisation (AMO) with appropriate rating. The AMO maintained the helicopter from 7 March 2008 to date. There were no anomalies identified with the organisation and management of the AMO involving the maintenance of the helicopter in the investigation.

1.17.7According to the AMO, the maintenance procedure which they used was in

accordance with Robinson Maintenance Manual Model RH44 Series, in this regard with Section 7 requirements.

1.17.8 South African Civil Aviation Authority (SACAA) - The responsibility of the authority

is to ensure that the following:

(i) According to International Civil Aviation Organisation (ICAO), Annexure 13, Part3 (3.1) which is the objective of the investigation – “The sole objective of the investigation of an accident or incident shall be the prevention of accidents and incidents. It is not the purpose of this activity to apportion blame or liability”.

(ii) According to Civil Aviation Regulations (CAR), Part 12 (12.03.1) which is the

purpose of the accident or incident investigation – “The purpose of investigation of an accident or incident is, subject to section 12 of the Act, to determine, in terms of the provisions of this part, the facts of an accident or incident in the interest of the promotion of aviation safety and the reduction of the risk of aviation accidents or incidents, and not to establish legal liability”.

1.17.9 The evidence shows that the Director of Civil Aviation (DCA) has approved the

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safety recommendations which Accident and Incident Investigation Division (AIID) brought before him on 18 March 2011 and August 2011. To date no implementation action was taken.

1.18 Additional Information 1.18.1 Intermediate flex plate: Power to drive the main and tail rotors is transmitted from

the engine to the rotor drive train through a v-belt drive system. 1.18.3 Flexible couplings are located at the input to the main rotor (also known as the

forward flexible couplings) and at both ends of the tail rotor drive shaft. The flexible coupling at the forward end of the tail rotor drive shaft is commonly known as the intermediate flexible coupling.

1.18.4 The flexible coupling in the RH44 drive train accommodates differences in drive shaft axial alignment during helicopter operation. They are constructed by bolting a single, four armed, thin stainless plate between the main rotor gearbox yoke and the drive shaft yoke.

1.18.5 Flex plate fracture control: The safe operation of the Robinson RH44 helicopter

depends on maintaining the integrity of the main rotor and tail rotor drive train during each flight. Torque from the engine is transmitted along a single load path to both rotors; no redundant load paths are provided.

1.18.6 The threat of coupling failure to flight safety is managed by flex plate replacement

after a prescribed period of time and correct assembly during manufacture and maintenance. The coupling is required to have sufficient strength to transmit the torque created during all phases of helicopter operation within the designed operational limits.

1.18.7 It is also required to have enough strength to resist the initiation and growth of

fatigue cracks under the local alternating stress state created by repeated torque application and repeated flexing of the plate during helicopter operation within the designed operational limits. In general terms, fatigue cracking occurs in response to exposure to a loading environment that creates alternating local stresses in a component. Crack initiation is dependent on the number and magnitude of the local alternating stress cycles. There is an adverse relationship between stress cycle magnitude and number of stress cycles to fatigue failure.

1.18.8 The threat of fatigue failure in the case of components subjected to many

alternating loading cycles for the duration of its expected life is controlled by limiting the magnitude of the local stresses developed at the bolt hole during operation to a value below the fatigue limit for the component. The fatigue limit for a component is a function of alloy strength, surface finish and detailed geometry, and in the case of the flex plate, the presence of bonded reinforcement.

1.18.9 The region surrounding each bolt hole is reinforced by adhesively bonded reinforcing plates. The magnitude of stress created at the edge of the bolt hole during helicopter operation is affected by the presence of the bonded reinforcing plates. Flex plate fracture control depends on limiting the magnitude of the local stresses at the flex plate bolt holes.

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1.19 Useful or Effective Investigation Techniques 1.19.1 None. 2. ANALYSIS 2.1 The Operator – Kriek Helicopters was conducting game or livestock cull operation

for the South African National Parks (SANParks). The game or livestock operation took place at one of SANParks National Parks. This was a commercial operation and the Operator was a service provider of SANParks. The Operator’s certification (air service license and air operating certificate) shows that they were appropriately authorised to provide the game or livestock cull service to SANParks which was in compliance with applicable regulation.

2.2 The pilot had valid Commercial Pilot License with RH44 helicopter type and game

or livestock cull ratings endorsements on it. The pilot’s total flying hours (1808.3) and flying hours “on type” (760.0) is proof of his aviation experience. The pilot also had a valid Class 1 aviation medical certificate with no waivers. There was no medical condition identified which may have prevented him from flying the helicopter on the day.

2.3 The pilot performed a preflight inspection on the helicopter to validate that it was

serviceable prior to the flight. There was no defect or malfunction experienced with the helicopter during the preflight inspection. The pilot was satisfied with the condition and performance of the helicopter; hence the decision he made to fly the helicopter to Graspan National Park for the game or livestock cull operation.

2.4 Ordinarily, in aviation the game or livestock cull operation involves a process of

using the helicopter to remove specifically identified animals (in this case - buffalos) from the herd for whatever reason determined by SANParks. The cull operation then continues or be repeated for as long as it’s needed until the identified selected animals are separated, darted and/or captured for the intended purpose.

2.5 Throughout the game or livestock cull process, the helicopter maintains flight at low

altitude (in this case - it was approximately 20 feet) above ground level, where it will follow the selected herd of animals. In these kinds of scenario, there is always the possibility of the pilot experiencing emergency situations. Therefore the pilot has to be alert and aware of his surroundings to execute an emergency landing. The safety of the helicopter, its occupants (in this case – the passenger which was a SanParks Veterinarian) and private property relies on the quick response from the pilot. Where the pilot have to identify the source of the emergency? What emergency procedures are required to correct the emergency? In the end, when all efforts to correct fail having to execute an emergency landing.

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2.6 The evidence shows that the pilot did whatever he could to avoid being involved in

the accident. As soon as he felt the vibration accompanied with the grinding/growling noise, he already identified the source to be probably a component failure. Him putting safety first, he immediately decided to execute an emergency landing. In the process of the emergency landing the helicopter sustained loss of power which resulted in a low rotor RPM (main rotor r.p.m decaying). The pilot applied collective control just before touchdown to cushion the landing. The helicopter landed hard and at the same time gone into an uncommanded nose over attitude. The pilot attempted to correct the nose over attitude by applying aft cyclic control to lift up the nose. The tail boom was lifted into the plain of rotation of the main rotor blades. The main rotor blades then struck the tail boom and severed it in two pieces. Fortunately at this time the helicopter settled down on its landing gear (skids) on the ground. The airframe (cockpit and cabin area) was still intact after landing. The helicopter sustained substantial damage to the tail boom in the impact sequence. The pilot and passenger survived the occurrence without any injury.

2.7 The helicopter was examined during the investigation process with the aim to

determine the course of the accident. There was evidence found which shows that a part: forward intermediate flex plate which is installed on the drive train of the helicopter failed during the flight. The flex plate connects the engine output to the transmission input within the drive train through a v-belt drive system. This explains the loss of power and main rotor RPM decaying. The failure of the forward flex plate resulted in the tail rotor becoming ineffective. The difference of the RPM between the main and tail rotor caused an imbalance which resulted in the vibration that was felt. The grinding/growling noise came from the disconnected tail rotor driveshaft which made scratch marks inside of the tail boom.

2.8 The flex plate that fractured was removed from the helicopter and taken for

metallurgical examination to determine the cause of the failure. The metallurgical examination report concluded that the flex plate failed due to fatigue cracking. The fatigue crack on the flex plate started at the bolt hole and propagated under the washers of the bolted joint towards the edge of the flex plate. It was also evident from the fracture surface features that the crack growth had occurred over a number of flights prior to the accident flight.

2.9 The helicopter’s maintenance documentation was reviewed during the investigation.

The evidence shows that the intermediate flex plate that failed was installed on the helicopter during the time of its assembly. The flex plate service life (1003.7 hours) was the same as that of the helicopter. The helicopter had mandatory periodic inspections (MPI’s) carried out on it after every 100 hours operation and/or annually whichever comes first. During the MPI’s the intermediate flex plate was subjected to visual inspection to verify its condition. The aim of the inspection on the flex plate was for fatigue crack detection. The flex plate condition was determined to be satisfactorily and no fatigue cracks were identified by the AMO.

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2.10 The time when it was discovered that the intermediate flex plate had failed. The flex

plate was removed from the wreckage and taken for metallurgical examination. The flex plate metallurgical report was then forwarded to the National Transport Safety Board (NTSB) for comment. The NTSB forwarded the flex plate metallurgical report to Robinson Helicopter Company, which is the manufacture of the RH22 and RH44 helicopter determined to be susceptible to these mechanical failures. The manufacture, response to the flex plate metallurgical report was that the probable cause of the failure may have been due to “ a maintenance issue and not a strength or durability issue”. The manufacturer highlighted “maintenance” based on the AMM requirement to support the tail rotor drive shaft during maintenance and avoid damage caused to affected flex plate. The manufacture interest was particularly directed to the maintenance carried out where the clutch actuator was replaced. The opinion of the manufacture was that the “ shaft would have needed to be supported the entire time the clutch actuator was o ut for repair or service”. Hinting that if the flex plate was not properly supported “the forward or intermediate flex plate could be damaged”. The manufacture explained that the fatigue crack on the flex plate appears to have initiated at the edge of the washer. If the driveshaft is allowed to move beyond its normal range of motion (up & down, left & right), the flex plates will of course exceed their intended range of motion and the area near the inboard edge of the washer is where the most stress is going to develop.

2.11 The investigation was then extended to the flex plate or driveshaft removal and

installation maintenance procedures included in RH44 aircraft maintenance manual (AMM). The AMM requires the following: “Support drive shaft through upper aft tail cone inspection hole to prevent damage and for alig nment purpose”. An anomaly was identified with the maintenance procedure. The maintenance procedure does not clearly identify the means of compliance, thus creating a situation whereby the support of the drive shaft are imparted differently by South African AMO’s which carry out maintenance on RH 22 and RH44 helicopters. The information of the inconsistent method of compliance relevant to what the AMM requires in terms of “supporting the driveshaft” was brought to the attention of the manufacture. The manufacture did not want to acknowledge or deny the issue as being a problem, but they insisted that the process of “support of drive shaft” was important during maintenance.

2.12 Currently in South Africa there are two accident reports of similar nature

(development of fatigue cracks that resulted in flex plate failure) which was investigated and approved by the South African Civil Aviation Authority (SACAA) through the office of the Director of Civil Aviation (DCA). The two accident reports had safety recommendations which were waiting for implementation by the DCA. The implementation of the safety recommendations would have had the effect to avoid having re-occurrence of the same type of accident happening. Unfortunately for reasons not known at the time of this accident, it was found that the safety recommendations had not been implemented or any attention given by the SACAA. The possibility exists that the probable cause of this accident, which is identically the same as the other two accidents could have been avoided or re-occurrence of the accident stopped.

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2.13 The SACAA developed an internal flow of safety recommendation procedure which

was approved by the Director of Civil Aviation (DCA). The implementation of the procedure was to ensure follow-up of safety recommendations from Accident and Incident Investigation Division (AIID). It would appear out of the findings of non-implementation of approved safety recommendations that the SACAA is not complying with requirements of the procedures.

3. CONCLUSION 3.1 Findings 3.1.1 The pilot had a valid Commercial Pilot License (CPL) and the aircraft type rating

(RH44) was endorsed on it. 3.1.2 The pilot had a valid Class 1 aviation medical certificate with no waivers. He did not

have any medical condition which may have prevented him from flying the helicopter on the day.

3.1.3 There were fine weather conditions that prevailed in the area at the time of the flight

and subsequent accident. 3.1.4 The helicopter was properly maintained by the AMO and there was no documented

evidence found indicating any defect and/or malfunction prior to the flight that could have contributed to or cause the accident.

3.1.5 The pilot accompanied by a passenger flew the helicopter on a commercial game or

livestock cull flight on the day when the accident occurred. 3.1.6 The helicopter was being operated at low altitude during the flight which was normal

operating height for game or livestock cull operations. 3.1.7 The pilot reported that he suddenly felt a vibration accompanied with a grinding –

growling sound from the helicopter during the flight. The identified condition resulted in him executing an emergency landing in an open field.

3.1.8 The helicopter landed hard, followed by rolling movement toward the left side due to

the left side skid getting stuck in the soil and in the process the main rotor blade struck the tail boom.

3.1.9 The helicopter sustained substantial damage during the emergency landing. 3.1.10 The evidence found during the onsite investigation showed that the helicopter

sustained a mechanical failure in flight which resulted in the accident. 3.1.11 During the wreckage investigation it was determined that the aft flex plate on the

drive train (tail rotor shaft) failed.

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3.1.12 The intermediate flex plate was removed from the wreckage and taken for

metallurgical examination. The result of the metallurgical examination was the following: It was evident that fatigue cracking in the flex plate started at the bolt hole and propagated under the washers of the bolted joint towards the edge of the flex plate. It was also evident from the fracture surface features that crack growth had occurred over a number of flights prior to the accident flight.

3.1.13 The metallurgical report detailing the information of the flex plate failure was

forwarded to Robinson Helicopter Company for comment. Their response was that “the failures are due to a maintenance issue and no t a strength or durability issue”.

3.1.13 There was evidence found of two other Robinson Helicopter (R22 and R44)

accidents previously in South Africa which probable cause was determined to be as a result of flex plate failures. Robinson Helicopter Company response was “ We have seen failures relating to fretting due to lack of torque on the hardware and the crack initiates at the bolt hole, but we ar e unaware of any other flex plate failures in this manner”.

3.1.14 There were safety recommendations made in the two previous accident reports to

prevent re-occurrence which was approved by the SACAA Director of Civil Aviation (DCA). The evidence found shows that the DCA approved safety recommendation were not implemented by the SACAA. The recommendations were as follows:

(i) It was recommended that the DCA instruct the Airworthiness Department of

SACAA to; in consultation with the FAA of USA review the need for defining of a service life of the forward flex plates as installed on Robinson R22 series helicopters and defining of an inspection interval of the forward flex plates as installed on Robinson R22 series helicopter.

(ii) In the interest of aviation safety, it is recommended that an urgent MAN

(Mandatory Aeronautical Notice) be issued as approved by DCA on 18 March 2011, to ground all South African registered Robinson R44 and R22 helicopters with immediate effect pending a proper inspection of the forward flex plates before any further flight and that the Airworthiness Section of SACAA compile an inspection procedure/method to carry out this inspection.

3.2 Probable Cause/s 3.2.1 Mechanical failure during flight which resulted in an emergency landing followed by

a hard landing. Contributory Factors 3.2.2 Forward flex plate failed due to fatigue crack developing at bolt hole underneath the

bonded washer. 3.2.3 Fatigue crack on forward flex plate not detected during maintenance inspection.

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3.2.4 Aircraft Maintenance Manual (AMM) limits flex plate crack detection to visual

inspection. 3.2.5 Non-implementation of previous Robinson Helicopter RH22 and RH44 flex plate

failure accidents safety recommendations approved by the Director of Civil Aviation (DCA) which was intended to stop re-occurrence.

4. SAFETY RECOMMENDATIONS 4.1 It is recommended that the Director of Civil Aviation (DCA) instructs the relevant

departments within the SACAA to implement the previously approved safety recommendations made concerning the Robinson Helicopter (RH22 and RH44) mechanical failures of flex plates fracturing from fatigue. Note -- previously approved safety recommendations.

4.2 It was recommended that the DCA instruct the Airworthiness Department of SACAA

to; in consultation with the FAA of USA review the need for defining of a service life of the forward flex plates as installed on Robinson R22 series helicopters and defining of an inspection interval of the forward flex plates as installed on Robinson R22 series helicopter.

4.3 In the interest of aviation safety, it is recommended that an urgent MAN (Mandatory

Aeronautical Notice) be issued as approved by DCA on 18 March 2011, to ground all South African registered Robinson R44 and R22 helicopters with immediate effect pending a proper inspection of the forward flex plates before any further flight and that the Airworthiness Section of SACAA compile an inspection procedure/method to carry out this inspection.

5. APPENDICES 5.1 Appendices A: Copy of Metallurgical Report of ZS-PXL. Appendices B: Copy of Synopsis of ZS-RVA Appendices C: Copy of Synopsis of ZS-SCS Compiled by: ....................................................... Date: ………………….……….. For: Director of Civil Aviation Investigator-in-charge: ……………………………… Date: …………………………..

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Co-Investigator: …………..………………………… Date: ……………….………… Appendices A: Copy of Metallurgical Report of ZS-PXL

CA 12-12a 25 May 2010 of 34

section/division occurrence investigation form number ...caa.co.za/accidents and incidents...

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