may–june 1999 managing aircraft-tire w ear and damage ... · pdf filew ear and damage...

MAY–JUNE 1999

F L I G H T S A F E T Y F O U N D A T I O N

Aviation Mechanics Bulletin

Managing Aircraft-tireWear and Damage

Requires Adherence toRemoval Limits

F L I G H T S A F E T Y F O U N D A T I O N

Aviation Mechanics BulletinDedicated to the aviation mechanic whose knowledge,craftsmanship and integrity form the core of air safety.

Robert A. Feeler, editorial coordinator

Managing Aircraft-tire Wear and Damage RequiresAdherence to Removal Limits ......................................................................1

Maintenance Alerts ..................................................................................... 13

News & Tips ............................................................................................... 16

May–June 1999 Vol. 47 No. 3

AVIATION MECHANICS BULLETINCopyright © 1999 FLIGHT SAFETY FOUNDATION INC. ISSN 0005-2140

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Managing Aircraft-tireWear and Damage Requires

Adherence to Removal Limits

Aircraft tire/wheel-assembly failuresinvolve various operational and main-tenance factors, but detectable dam-age to one or more tires sometimes isthe underlying cause. Such failuresoccur infrequently; nevertheless, cor-rectly maintaining tire components —whether in a new tire or a retreadedtire — helps ensure that tire/wheelassemblies will perform reliably un-der high static loads and dynamicloads. The airframe manufacturer’sprocedures typically specify limits forwear and damage.

Airlines typically establish tire-maintenance procedures that

anticipate the use of products fromdifferent tire manufacturers. Theprocedures are written to complywith applicable regulations and safepractices developed by airframe,wheel and tire manufacturers. When-ever the safety of a tire is in question,the tire should be removed from ser-vice and should be sent to a certifiedrepair-and-retread station for furtherinspection and disposition.

For most tire anomalies, a consensusbased on experience and testing in theaviation industry guides an appropri-ate response or a range of appropriateresponses. Separation of plies and

FSF Editorial Staff

2 FLIGHT SAFETY FOUNDATION • AVIATION MECHANICS BULLETIN • MAY–JUNE 1999

tread or tire bulges, for example,require immediate removal of the tirefrom service. Nevertheless, differencesin perception or in the evaluationcriteria applied by flight crews andmaintenance crews sometimes gener-ate questions about airworthiness, asshown in the following incident report.

The report to the U.K. ConfidentialHuman Factors Incident ReportingProgram (CHIRP) in 1998 said, “Dur-ing completion of the exterior inspec-tion prior to departure, I noticed thatthe right nose-wheel tire [of a Boeing777] was bald with several cuts downto and, in one case, through the tirecords. An inspection of the technicallog shows that the [extended-rangetwin-engine operations (ETOPS) pre-departure check], transit [predeparturecheck] and ramp check had beensigned off as satisfactory. A verbalquestion to the ground engineer as tothe serviceability of the nose wheelreceived the response, ‘Oh, that’s OKfor lots more landings.’ Only when Ientered a defect in the tech log tothe effect of ‘Please confirm service-ability of right nose wheel’ [was] awheel change … called for. It was thenapparent that … nose wheels were outof stock and that one needed to beobtained from an outside contractor.A two-hour delay resulted. I am surethat commercial pressure played astrong part in the attempt to dispatchthe aircraft in this state. But two peo-ple had to sign the relevant checks andinspections in the tech log, and I am

sure that at least one of the signatorieswas signing for someone else’s work.(CHIRP note: This incident was inves-tigated by the airline and the tire was,in fact, serviceable, with two millime-ters [(mm); 0.079 inch] of tread re-maining over more than 75 percent ofthe tire. The ‘cuts’ referred to by thereporter were ozone-induced cracksand were acceptable. The airline hassince issued [tire-tread] depth gaugesto be used on this [aircraft] type).”1

The report shows that some anoma-lies in tire/wheel assemblies are “ac-ceptable conditions” and are notcause for removal of the tire fromservice. Maintenance techniciansmust communicate clearly the ap-proved tire-maintenance proceduresand the applicable wear limits ordamage limits in a given situation.For example, spiral wrap — the rein-forcing cords wound into the tread ofsome retreaded tires to reduce chev-ron cutting and tread chunking —typically begins to show as a tirewears, but the appearance of thesecords does not compromise safety.(See “Limits for Tire Damage AlsoInvolve Common Principles” on page9 for a discussion of chevron cuttingand tread chunking.)

Deviations from approved tire-maintenance practices — including as-sessment of wear and damage — havepotentially serious consequences. Sep-aration of tires and tire treads from tire/wheel assemblies has been cited as a

FLIGHT SAFETY FOUNDATION • AVIATION MECHANICS BULLETIN • MAY–JUNE 1999 3

causal factor in some accidents andincidents. Typically, the reports do notsay whether the underlying damage orwear could have been detected priorto the event.2 Nevertheless, one typi-cal consequence with adverse safetyimplications has been tire-tread delam-ination on takeoff, with various de-grees of foreign-object damage toaircraft engines, control surfaces andother components.

The accident and incident reportingsystem (ADREP) maintained by theInternational Civil Aviation Organi-zation (ICAO) contained the follow-ing events involving various types ofdamage that originated in one or moretires:

• The report for a March 1992 in-cident involving a tire failure ona Boeing 737-400 during take-off from Milan, Italy, said, “Ontakeoff, just after V1, the pilot felta slight bump. The crew wereunaware of any damage until the[air traffic] controller advisedthem of debris on the runway anda passenger reported damage tothe right wing. The pilot rea-soned that the right main gearhad suffered tire damage anddiverted to [London StanstedAirport, England]. A tendency toroll to the right dictated a 30-degree flap landing, but a safelanding was made. The tread ofthe right outboard main-wheeltire had separated completely,

although the tire remained in-flated throughout the landing.Half of the right gear-leg doorhad been torn off, and the in-board flap assembly was dented.A falsework [access] panel onthe wing undersurface was alsodamaged, and the inboardground spoiler had a 10-inch[25-centimeter (cm)] hole in thetrailing edge. The tire, which wason its second retread, failed af-ter 236 landings. Examination ofthe tire tread indicated a numberof cuts consistent with the tirehaving run over a foreign object.It was not possible to establishwhere or when the tire had suf-fered the damage, which led tothe tread failure, although it waslikely to have been within the lastone or two departures.”

• The report of a June 1990 inci-dent involving a tire failure on aMcDonnell Douglas DC-9-50during takeoff from Atlanta,Georgia, U.S., said, “Duringtakeoff, the no. 4 tire blew. Theaircraft returned and landed safe-ly. Damage to the [tire] innerliner consistent with underinfla-tion was found. The maintenanceprogram for the operator re-quired tire pressure to be checkedwith a gauge during layover in-spections. The inspection wasdone the previous day. Recaprecords revealed that the tire wasrecapped and delivered to the


operator with a pinhole in the lin-er which allowed a slow leak.The pinhole was not repairedbefore delivery to the operator.”

• The report for a July 1996 inci-dent involving failures of six tireson a Tupolev Tu-154M/Tu-164during takeoff from Delhi, India,said: “During the takeoff run, asthe aircraft accelerated throughabout 150 kilometers per hour[81 knots], the crew heard a‘bang,’ and the aircraft began toveer to the right. The takeoff wasaborted, and the aircraft [was]brought to a safe stop on the run-way. It was subsequently dis-covered that four tires on theright main undercarriage and two[tires] on the nose had failed. Theaccident happened in darkness(0010 local time) but in visualmeteorological conditions [with]temperature 28 degrees Celsius[(C); 82 degrees Fahrenheit(F)].… The tire failure is said to havebeen caused by the allegedlypoor condition of the runwaycoupled with the premature ag-ing of the tires due to the aircraftbeing parked at Delhi for longperiods in excess of 40 degreesC [104 degrees F].”

• The report for an August 1997incident involving a tire failureon an Airbus A300 during take-off from Los Angeles, California,U.S., said, “During takeoff at145 knots, the crew heard a loud

noise. The pilot aborted the take-off. Pieces of rubber from [the]no. 3 tire were found in [the]no. 2 engine. The engine fan wasdestroyed, and several … guidevanes were damaged.”

A report to CHIRP in 1998 showedthe value of careful observationthroughout the tire-maintenance pro-cess. The report said, “Due to an acuteshortage of certifying engineers, Ifound myself working a ‘ghoster’[working a night shift immediatelyafter a day shift]. During the dailyinspection on a nightstop aircraft [anaircraft left overnight] the no. 1 main-wheel tire was found to be ‘worn tolimits.’ The main wheel was replacedby myself and the paperwork com-pleted. A mechanic then took theunserviceable wheel to the goods out-wards area. It was then that he no-ticed a locking spacer still attachedto the unserviceable item, whichshould have been transferred to thereplacement wheel. The situation wasquickly rectified with the spacer be-ing fitted to the aircraft. If the spacerhad not been fitted, the main wheelwould have been free to move alongthe axle and disengage from one ofthe rotors on the brake pack. I had notnoticed my error, and, with hindsight,was too fatigued to safely certify thetask and the aircraft.”3

Criteria for judging aircraft-tirewear and damage vary amongcivil aviation authorities, airframe


manufacturers, tire manufacturers andairlines. Nevertheless, several princi-ples are universally applicable, withregular preflight inspection as the foun-dation. Many airlines and regulatoryauthorities consider daily inspection oftires — including checks of pressurewith calibrated gauges — essential forsafe operation. Visual inspection oftire/wheel assemblies after every land-ing or at every turnaround also isrecommended as a good practice.

Successful tire maintenance requiresadherence to a program that includesnot only the regular-interval checksand preflight inspections, but also thor-ough inspections of demounted tires(and tubes, if applicable). Policies andprocedures also should specify howtire/wheel assemblies will be removedfrom aircraft and inspected followingabnormal events such as rejected take-offs, hard landings, excessive brake-heat generation or failure of the othertire/wheel assembly on that axle. Dis-position of tires based on suchinspections should be explicit, andcompliance should be documented.

Safety procedures for all inspectionsof tire wear and tire damage shouldbe followed carefully and consistent-ly. A tire/wheel assembly that obvi-ously has been damaged, for example,should be deflated by a remote meansafter cooling for at least three hours.Maintenance technicians also shouldfollow approved safety instructionsfor approaching any tire/wheel

assembly in service. Some specialistsrecommend approaching tires froman oblique angle in the direction ofthe tire’s shoulder (the edge where thetread meets the sidewall). Other au-thorities recommend approaching inthe direction of the tire tread; that is,not in the direction of the sidewall.

Some forms of damage are insidiousbecause they are difficult to detectvisually or develop slowly with nosymptoms. For example, long-termoperation of tire/wheel assemblies atless than specified operating pressuregradually weakens tires; use ofgreater-than-normal braking energymay cause internal structural damageto tires; and the effects of bottominga tire (wheel flange contact with therunway) on landing may not becomeapparent until symptoms appearseveral landings later.

Tires should remain mounted and in-flated, however, until inspections havebeen completed and suspected dam-age areas have been marked with achalk stick, light-colored crayon, waxmarker or paint stick, and the reasonfor removal from service has beenwritten on a tag attached to the tire.

Normal-wear BaselineSimplifies Problem

Detection

Aircraft manufacturers, regulatory au-thorities, tire manufacturers, operators


and various engineering-standards andtechnical organizations issue proce-dures, criteria, photographs and othertools for systematically judging wheth-er or not any wear limits or limits oftire damage have been exceeded.

The following principles concerningtire wear and damage generally ap-ply to aircraft tire/wheel assemblies,but aircraft maintenance manuals,component maintenance manualsand technical bulletins should be con-sulted for any specific aircraft:

• All tires (and tubes, if used)should be inspected immediate-ly after delivery by qualified tire-shop personnel for damage fromshipping, handling or storage.Such damage could include cuts,tears or foreign objects penetrat-ing the rubber; cuts, contamina-tion or wrinkling of the innerliner; bulges and permanentdeformations; debris or cuts onthe bead seating surfaces; beaddistortions; cracking that reach-es cords; and rubber-attackingcontaminants (especially hydro-carbon products such as fuel, oil,grease, brake fluid or solvents)that can cause visible blisters orswelling. Appropriate tables oflimits for cut length and cutdepth should be consulted to de-termine whether a cut or crack isacceptable;

• A bulge in the tread or sidewalltypically warrants immediate

removal of the tire from service.Bulges often indicate cord-bodydamage, or internal separation oftread or plies. Areas that showbulges must be marked careful-ly before deflating the tire to en-able identification later;

• If the fuse plug of a tire/wheelassembly melts and releases ni-trogen while a tire is rolling,some procedures require the tireand its axle mate to be taggedimmediately as unsuitable forfurther service and discarded;

• Any rub marks on tires, gear orwheel wells require verificationof adequate clearance for the tire/wheel assembly;

• Hydrocarbon contaminantsshould be removed from thetire according to specifications,then possible damage should beassessed by pressing the contam-inated area to detect abnormaltexture (sponginess or softening).Such damage warrants removal ofthe tire from service.

Limits for Tread WearEmphasize Variation

From Expected Patterns

Tread depth on aircraft tires affectscontact with runways and taxiwayssimilar to the way automobile tires“grip the road.” Tread grooves alsomust be deep enough for water to passunder the tires, minimizing the risk


of skidding or hydroplaning on wetrunways. Inspections usually includedescriptive visual criteria and wearvalues that can be measured with atread-depth gauge — typically cali-brated in thirty-secondths of an inchand/or in millimeters — according tomanufacturers’ specifications.

A basic principle of tire inspection isthat the tread should show a normalwear pattern, which is relatively evenover time. Achieving this requiresstrict use of specified operational in-flation pressures and consistent main-tenance practices. In normal wear, thewear limits are reached first along thecenterline of the tire tread. Accentuat-ed centerline wear is the typical symp-tom of overinflation. Accentuatedshoulder wear is the typical symptomof underinflation. Correct balancing ofthe tire/wheel assembly also is impor-tant. Imbalance can cause severe vi-bration and irregular tread wear.

During normal wear of a retreadablebias-ply tire, gradual removal of treadfirst exposes the tread-reinforcing ply.Beneath this ply is the undertread lay-er, and beneath that layer are carcassplies. During normal wear of a retread-able radial tire, gradual removal oftread first exposes the protector ply. Be-neath this ply is the undertread layer,followed by belt plies and carcass plies.

For both types of tire construction,tread-wear criteria for retreadabletires typically cite that wear must not

expose more than a specified amountof tread-reinforcing ply (bias tire) orprotector ply (radial tire) to keep atire in service. Assessment of damage,however, may include detailed crite-ria for measurement of penetration.

Criteria for measuring and evaluatingtire wear should be obtained fromthe airframe manufacturer’s aircraftoperations manual, aircraft mainte-nance manual, service bulletins andsimilar approved documents for thespecific aircraft. Among other topics,the aircraft operations manual typi-cally specifies whether return-to-baseflights are permitted if tires reachspecified wear limits on an aircraft ata remote location, and under whatoperating conditions. More conserva-tive wear limits might be specified foraircraft operating conditions thatcould cause hydroplaning.

One major manufacturer, for exam-ple, recommends the following wear-removal criteria for the company’sproducts based on examination of thefastest-wearing area along the tread:4

• The wear limit for nonretread-able tires is the first appearanceof casing cords (any amount ofexposed casing-cord area) forbias-ply tires or the first ap-pearance of belt-ply cords (anyamount of exposed belt-ply cordarea) for radial tires; and,

• Retreadable tires should be re-moved from service before the


wear exceeds the retreadablelimit. This limit is when the wearlevel reaches the bottom of anytread groove along more thanone-eighth of the circumferenceon any part of the tread, or thetread-reinforcing ply of a bias-ply tire or the protector ply of aradial tire is exposed for morethan one-eighth of the circumfer-ence at a given location.

The following special types of treadwear also have limits:

• Tread-rubber reversion, skid burnand flat spotting (typically ovalareas where abrasion and exces-sive heat generation have convert-ed tread rubber to the uncuredstate or caused localized tread-rubber loss) occur for several rea-sons, such as when a brake lockupoccurs or the aircraft skids on awet or ice-covered runway. Tiremanufacturers specify criteria forevaluating this type of wear, suchas whether a specified amount ofcord-ply fabric has been exposed.For flat spotting, for example, onemanufacturer recommends con-tinued use of the tire except whenthe worn area exposes any of thereinforcing ply of a bias-ply tireor the protector ply of a radial tire,or this rubber loss causes aircraftvibrations.

• Asymmetrical (laterally uneven)tread wear — which may occur

from misadjustment of landinggear, poor taxi technique or oth-er reasons — sometimes can becorrected by reversing the tire’sposition on the wheel.

Another tire manufacturer said that atire should be removed from servicewhen the tread has worn to the baseof any groove at any spot, or to adepth shown in the aircraft mainte-nance manual. Another general ruleis that tires worn to fabric in thetread area should be removed fromservice regardless of the amount oftread remaining.5

Most tires used by airlines aredesigned for a service life encom-passing multiple remanufacturing (re-treading) cycles because the tire-cordbodies wear more slowly than treadsin normal operations. Control of qual-ity and safety is performed under theregulations of applicable airworthi-ness authorities. Some authoritiesspecify a maximum number of re-tread cycles. Others rely on approvedprograms in which certified techni-cians consult records and use quality-control tests to determine when anytire-cord body exceeds safety limitsfor further retreading. In the UnitedStates and Europe, regulations of theFederal Aviation Administration(FAA) and the Joint Aviation Author-ities, respectively, require retreadingand/or repairing of aircraft tires incertified retread-and-repair stations,which employ certified technicians,


maintain service histories of indi-vidual tires, and can repair manytypes of damage if cords have notbeen cut or damaged.

Tests to determine a tire’s suitabilityfor retreading require demounting thetire/wheel assembly and removing thetire. A separate category of tire-wearlimits and damage limits applies toassessment of demounted tires for thepurpose of determining retreadability.(Retreading limits established by theoriginal tire manufacturers are be-yond the scope of this article. Never-theless, within these limits, tireswith evenly worn tread, with a flat-spotted tread or with numerous cutsin the tread area typically are accept-able for renewal of the tread alone orfor renewal of a bias-ply tire’s treadand reinforcing ply or a radial tire’stread and protector ply.)

Limits for Tire DamageAlso Involve

Common Principles

The Society of Automotive Engineers(SAE) in 1995 published guidelinesrepresenting currently accepted in-dustry practices regarding damageto bias-ply aircraft tires, the mostwidely used type of tire construction.SAE’s guidelines did not includeradial tires, but recent tire care andservice literature from several majortire manufacturers shows that simi-lar principles apply to radial tires.

SAE’s recommended practice — likemajor tire manufacturers’ care andservice publications — focuses on theprimary areas where tire damage mayoccur: the tread, the sidewall, the beadarea and the inner liner.6

The following factors are consid-ered important by developers ofSAE’s recommended practice, thecivil aviation authorities and sever-al major tire manufacturers. Main-tenance technicians are responsiblefor determining whether any guide-line is applicable to any specificaircraft or operating conditions,and how to comply with the air-worthiness requirements of aviationauthorities.

In the tread area, cuts, cracks,foreign objects or other tread anom-alies (called “injuries”) should beevaluated based on length and widthof each injury on the outermostcord-body ply; the number of inju-ries that meet or exceed these dimen-sions; the extent (percentage) ofpenetration of any injury through thecord-body plies; and the relative po-sition of injuries that exceed a speci-fied cord-penetration limit along thecircumference of the tire.

One of the most serious problems istread separation, a splitting or voidbetween tread and tread-reinforcingcomponents caused by the failure oftread adhesion. Tread separation typ-ically warrants removal of the tire


from service. Tests by tire manufac-turers have established that excessiveheat generation in tire/wheel assem-blies from underinflation or overload-ing are significant causes of treadseparation. Some manufacturers re-fer to one type of tread separation —tread delamination — to describe par-tial or complete loss of the tread tothe tread fabric ply or casing plies.

Pieces of glass, stones, metal and oth-er foreign objects embedded in thetread or penetrating the cord bodyshould be marked for removal. Re-moval should be done using correcttools and techniques (including ap-proved eye protection) after the tirehas cooled to ambient temperatureand has been deflated.

One manufacturer’s damage limitscall for removal of a tire if cord-plyfabric can be seen without spreadingthe cut or if cuts extend more thanhalf of the width of a rib and deeperthan 50 percent of the remaininggroove depth. Another manufactur-er’s limits are linked to exposure orpenetration of the casing-cord bodyof a bias-ply tire or the tread-beltlayers of a radial tire, specify a max-imum diameter for superficial open-ings by foreign objects, and requiretire removal if a tire cut or injury sev-ers a tread rib or extends across atread rib. Tread cuts may progress toa peeled rib (partial or total circum-ferential delamination of a tread rib)or rib undercutting, in which groove

cracking extends under a tread-ribcut. Limits to determine whether a tiremust be removed from service maybe linked to the extent of exposure ofreinforcing ply (on bias-ply tires) orprotector ply (on radial tires), or maybe linked to exact measurements ofcracking, peeling or undercutting.

The appearance of cord-ply fabricalso may warrant removal of a tirewhen tread chipping or tread chunk-ing (missing pieces of tread) arefound, circumferential cracking oc-curs at the base of a tread groove, orchevron cutting is observed (causedby some cross-grooved runway sur-faces). A crack in the tread where atread joint or splice separates in aradial direction — open tread splice— also warrants tire removal.

For the sidewall area, SAE’s recom-mended practice and an FAA advisorycircular7 generally consider normalweather checking or ozone checking(random shallow surface cracks), radi-al and circumferential cracks, shallowcuts, gouges and snags to be repairableif these anomalies do not exceed spec-ifications for penetration of the rein-forcing plies (for example, deeper thanone ply). Nevertheless, as in the treadarea, several anomalies warrant imme-diate removal of a tire from service.These include separation of sidewallrubber from the casing fabric and rup-ture of the tire casing at the sidewall.One insidious type of sidewall damage(that is, an initially invisible damage


that may compromise safety over time)is a lower-sidewall compression flexbreak. This break may begin withcracks on the inner liner side, thenweaken the tire through pressure loss.Underinflation of tires and overload-ing of tires are recognized causes ofsidewall damage. Pressure loss thatcannot be traced to another cause maybe a symptom of lower-sidewallcompression flex break. Demountingof the tire and inspection using anapproved checklist are appropriate todiagnose the problem before carcassplies severely deteriorate and cause amassive sidewall-ply separation.

In the bead area of the tire (the in-side edge that seals against the wheelflange) repairability is determinedby ruling out damage to cord-bodyplies and verifying that the tire-to-wheel fit will retain the specifiedinflation pressure. The bead-areasurfaces should be smooth, and wearshould be within limits. Tire-toolchafing or chafing by the wheelflange should not adversely affectcord plies or cause ply separation.In the bead area, hoops of steel wirecalled “wire beads” anchor the cas-ing plies and provide a strong mount-ing surface for contact with thewheel flange. Among serious prob-lems that typically warrant scrappingthe tire — that is, permanent removalfrom service because even basicretreadability limits would beexceeded — are protruding or exces-sively kinked bead wire, bead-wire

separation and damage from exces-sive heat generation (such as melt-ed, blistering or brittle rubber, orsolidified cord-ply fabric).

Inner-liner damage and splices shouldbe assessed for length, number andposition. Deterioration that warrantsremoval of the tire from service mayinclude distorted and wrinkled rub-ber in a tubeless-tire inner liner; fab-ric fraying and broken cords in atube-type tire inner liner; and linerblisters or liner separations that ex-ceed removal limits regarding size,position and number. Small liner blis-ters (diameter not more than twoinches [five cm]), particularly in tube-less tires, typically should be left asfound to avoid creating a slow leak.

Some tire wear and tire damage in-volve causal factors that can becontrolled, including improper main-tenance and improper pilot technique.Moreover, the resulting tire failurescan cause significant damage thatleads to an incident or accident. Lineexperience and tests by airframe andtire manufacturers have demonstratedthat sound principles for managingtire wear and tire damage effectivelyincrease the margin of safety in air-line operations.♦

References

1. The CHIRP Charitable Trust.“Aircraft Tires (Wheels).” U.K.


Confidential Human FactorsIncident Reporting ProgramSearch Request No. 99/3/02,March 25, 1999. The search, re-quested by Flight Safety Foun-dation, found two deidentifiedreports.

2. Examples in this article were se-lected from three databases.The data included air carrierincidents and accidents fromJanuary 1983 to January 1999,maintained by the U.S. FederalAviation Administration (FAA)and the U.S. National Transpor-tation Safety Board (NTSB),and the accident and incidentreport system (ADREP) main-tained by the International CivilAviation Organization. Narra-tive information did not providecausal factors consistently.Nevertheless, studies by tiremanufacturers have associatedsome of the types of tire/wheel-assembly failures with abnormaltire wear and tire damage.FAA and NTSB reports weredeveloped from official recordsby Air Data Research, 13438Bandera Road, Suite 106,Helotes, Texas 78023 U.S.

3. The CHIRP Charitable Trust.

4. Michelin Aircraft Tire Corp.Aircraft Tire Care & Service.Greenville, South Carolina, U.S.:Michelin Aircraft Tire Corp.,1997.

5. Aviation Products Division,The Goodyear Tire & RubberCo. The Comprehensive Guideto Aircraft Tire Care andMaintenance. Akron, Ohio, U.S.:The Goodyear Tire & RubberCo., 1998.

Aircraft Tire Sales Department,Bridgestone Corp. Tire Speci-fication & Maintenance Manual.Tokyo, Japan: Bridgestone Corp.,1997.

6. Society of Automotive Engineers.“Aircraft New Tire Standard: Biasand Radial.” Aerospace StandardNo. AS4833. June 1995. “AircraftTire Retreading Practice: Biasand Radial.” Aerospace Recom-mended Practice No. ARP4834.November 1995. Warrendale,Pennsylvania, U.S.

7. FAA. “Chapter 9: LandingGear Systems.” Airframe andPowerplant Mechanics AirframeHandbook. Advisory Circular65-15A. 1976.


Autopilot-switchMalfunction Causes

Airplane Upset

The U.S. National TransportationSafety Board (NTSB) said that an in-flight upset of a McDonnell DouglasDC-10-10 was caused by a mal-functioning control-wheel-steering(CWS) sensor that sent erroneoussignals to the autopilot. NTSB rec-ommended modification of the sen-sor and education of flight crews onthe potential for similar upsets.

The DC-10, operated by ContinentalAirlines, departed from Los Angeles,California, U.S., on May 21, 1998,and was climbing through Flight Lev-el 310 when an uncommanded pitch-attitude increase occurred.

The captain immediately discon-nected the autopilot. “Flight datarecorder (FDR) data showed that theairplane then went through fourup-and-down pitch oscillations, themost severe of which attained verti-cal accelerations of +1.84 [Gs] to–1.12 Gs,” said NTSB.

The first oscillation occurred imme-diately after the uncommanded pitchup. “Three more complete nose-upand nose-down cycles occurred … asthe flight crew tried to regain level

flight, because the peak airplane re-sponse lagged behind the peak flight-crew inputs by up to one second,” saidNTSB.

“This significant lag in airplaneresponse led to an airplane-pilotcoupled response in which the flightcrew was continuously out of phasewith the airplane’s motions. Threeoscillations were completed beforethe flight crew was able to dampenthe airplane’s response and return tolevel flight.”

Of the 298 occupants, three occu-pants (flight attendants) were seri-ously injured, and five occupantssustained minor injuries. The air-plane was not damaged. After theupset, the crew dumped fuel, re-turned to Los Angeles and landedthe airplane without further incident.

“Postflight examination of the air-plane revealed that the CWS sensorlocated in the first officer’s controlcolumn was malfunctioning andsending an erroneous signal to theautopilot computer,” said NTSB.

The malfunction resulted from ashort circuit caused by material con-tamination. Silver, chlorine andsulfur were found inside the CWSsensor. NTSB said that the mostlikely sources of the silver were

MAINTENANCE ALERTS


gold-plated silver wires connectingstrain gauges with the sensor.

The sensor manufacturer, KuliteSemiconducter Products, in 1975began to use gold wires or gold-plated platinum wires, rather thangold-plated silver wires.

NTSB recommended that the U.S.Federal Aviation Administration re-quire DC-10 operators to replacegold-plated silver wires with goldwires or gold-plated platinum wires,and to ensure that DC-10 flight crewsare provided information regardingthe potential for airplane upsetscaused by CWS-sensor malfunctionsand the potential for overshoots inrecovering from upsets, caused bythe airplane’s lag in responding tocontrol inputs.

Lightning DamageSpurs Call for ActionOn Bonding Straps

The U.S. Federal Aviation Adminis-tration (FAA) should review the de-sign of the horizontal-stabilizer-hingebonding straps on Fokker 70 and 100airplanes, and require operators tomodify their airplanes to increaselightning-strike protection, said theU.S. National Transportation SafetyBoard (NTSB).

The recommendation was generatedby the investigation of a Feb. 26, 1998,

accident involving a US AirwaysFokker 100. The airplane was substan-tially damaged during an emergencylanding at Birmingham (Alabama,U.S.) International Airport.

“The flight crew had declared an emer-gency because of a dual hydraulic-system failure that occurred after theairplane was struck by lightning,” saidNTSB.

A misinstalled connector in the al-ternate brake system caused thebrakes to lock when the crew appliedbrake pressure on landing. “Threemain-landing-gear tires failed, andthe airplane departed the runway,slid through the grass and came torest on an adjacent taxiway,” saidNTSB. None of the 92 occupantswas injured.

The right side of the fuselage hadnumerous small lightning-burnmarks, and the right horizontalstabilizer had a large lightning-burnmark. The horizontal-stabilizer-hingebonding strap, which provides a low-resistance path to allow electrical cur-rent to safely discharge, had beenmelted by an electrical overload.

“Once the bonding strap failed onthe accident airplane, the remainderof the electrical current arced acrossthe hydraulic lines in the verticaltail, which led to their failure,”said NTSB. The no. 1 hydraulic-system pressure line and the no. 2


hydraulic-system return line had0.25-inch-diameter (0.64-centimeter-diameter) holes, and both hydraulicreservoirs were empty.

Control Problem LeadsTo Off-airport Landing

On May 22, 1998, the pilot of aPiper Warrior made a precautionarylanding near Ripple Village, Deal,Kent, England, after aileron controlbecame restricted. The pilot sustainedminor injuries, his passenger was nothurt, and the airplane was substan-tially damaged. Investigators foundthat the autopilot switch functionedintermittently.

The U.K. Air Accidents InvestigationBranch (AAIB), in its report on theaccident, said that the private pilotconducted a full-and-free controlcheck before departure. During theflight, the low-voltage indicator lightilluminated.

“The pilot reported that the ammeterindication remained normal and noother electrical services appeared tohave been affected,” said the report.The pilot reduced electrical loads butcontinued using the autopilot with theheading-hold mode engaged.

The pilot later selected the autopilotoff and then found that he couldmove the control yoke partially to theleft but not to the right. “The auto-pilot was checked and confirmed tobe disengaged,” said the report. “Thepassenger [also a private pilot]checked his controls and confirmedthe restriction.

“The pilot reported that even withconsiderable force, it was not possi-ble to move the yoke to the right, al-though full control of rudder andelevators appeared to remain avail-able. The decision was taken to makea precautionary landing in the near-est suitable field.” The left wing sep-arated from the airplane during thelanding.

Initial examination of the airplanerevealed no flight-control-systemanomalies. The autopilot then wasremoved from the airplane and test-ed at an autopilot-overhaul facility.

“Functional testing was carried outwith particular reference to the actionof the unit’s controls during disen-gagement,” said the report. “It wasfound that the on-off switch was notalways positive in its action, with atendency to stick in both the ‘on’ and‘off’ positions.”♦


Process RestoresAcrylic Transparencies

The Clearfix™ Acrylic RestorationProcess enables maintenance tech-nicians to repair scratch damageto stretched-acrylic cabin windowson aircraft. The process makesscratches disappear on the majorityof noncoated-acrylic transparencysurfaces without causing optical dis-tortion, removing significant amountsof acrylic or degrading the strengthor durability of windows, said themanufacturer.

Two solutions containing abrasives,suspension agents and surfactants(surface-active agents) are appliedin sequence with hard and soft appli-cator pads mounted on a variable-speed power drill. The abrasive gritin the solutions gradually becomessmaller during the process. Transpar-encies are cleaned with the product’santistatic cleaner before, during andafter applying the solutions.

Product testing has been performedby the University of Dayton ResearchInstitute, and regional airlines andother aviation organizations havefield-tested the process. Technicalapprovals also have been obtainedfrom major aircraft manufacturers,said the company.

For more information: Clearfix Corp.,150 E. 58th St. 34th Floor, New YorkNY 10155 U.S. Telephone: +1(212)861–3161.

Training ProgramProbes Maintenance

Human Factors

Error management is the subject ofEngineering Solutions to HumanProblems, a new training program formaintenance technicians, maintenancemanagers, safety managers, engineers,maintenance apprentices and main-tenance trainees.

The program helps to fulfill require-ments for human-factors training oflicensed engineers, said the Interna-tional Federation of Airworthiness(IFA), which provided technicalsupport and financial support forproduction of the program.

The requirements for human factorstraining of licensed engineers arein International Civil Aviation Orga-nization Annex 1 amendment no.161. The amendment requires alllicensed engineers to have knowl-edge of “human performance andlimitations relevant to the duties ofan aircraft maintenance holder,”said IFA.

NEWS & TIPS


The program comprises 11 elements,including four videotapes, briefingand training materials, case historiesand human-factors study materials.

The program was produced by TVCTelevision Communications. Theprogram costs US$3,500.00; IFAmembers receive a 10% discount.

For more information: TVC Televi-sion Communications, 15 GreekStreet, London WIV 5LF. Telephone+44 171 734 6840.

Device MeasuresViscosity of

Turbine-engineLubricant

VIS-PROBE is an on-site test devicedesigned to test oil viscosity andprovide pass/fail results within10 minutes. The device can be usedto test lubricants for aircraft turbineengines, ground-based turbine en-gines and helicopter gearboxes, saidthe manufacturer.

VIS-PROBE is supplied with a certificateof calibration and the manufacturerstates that the product accommodatesall turbine-engine oils, including PRF-23699 and DOD-L-85734 types. Useof the device requires minimal training.

For more information: AirborneAnalytical Labs, P.O. Box 518, EastHanover, NJ 07936. Telephone (800)989-7692 (U.S.); +1(973) 887-7410ext. 235 (international).

Airborne Analytical LabsVis-Probe

Niagara CutterOptimizer™

Machining InformationOn CD-ROM

Niagara Cutter’s Optimizer™ inter-active CD-ROM provides productinformation, engineering charts anddemonstration videos. Topics includemetal-removal milling techniques andrecommendations, sharpening andinspection data, a quick-referenceengineering-chart list, and a guide toend-mill styles.


Also included are a video of thecompany’s end-mill manufacturingprocesses and a short demonstrationvideo showing the chip evacuation andperformance of coated end mills.

For more information: NiagaraCutter, 200 John James AudubonPkwy, Amherst, NY 14228 U.S.Telephone +1(716) 689-8400.

Filters MaintainCompressed-air

System Efficiency

LA-MAN Corp. supplies filter-replacement kits for its Extractor/Dryer® two-stage compressed-air-line filtration systems. Routine fil-ter replacement helps maintaincompressed-air systems and air-operated tools and ensures that theycan operate more efficiently, saidthe manufacturer. The kits includefirst-stage and second-stage filter

elements to remove moisture andcontaminants, a honeycomb basecore, gaskets and seals.

For more information: LA-MANCorp., 700 Glades Court, PortOrange, FL 32127 U.S. Telephone:(800) 348-2463 (U.S.); +1(904) 304-0411 (international).

DuPontSONTARA EC®

Industrial Wiper MadeOf Engineered Cloth

SONTARA EC® brand engineered-cloth wipers made by DuPont are suit-able for aircraft-maintenance usesincluding general-purpose cleaningand surface preparation in prepaint ap-plications, said the manufacturer.

SONTARA EC is a spun-lace wiperthat resists abrasion and solvents,contains no binders or glues, is low-linting, and is highly absorbent inwater, oil and solvents.

For more information: DuPont SontaraTechnologies, 1002 Industrial Rd., OldHickory, TN 37138 U.S. Telephone

LA-MANFilter Replacement Kits


(888) 476-6827 (U.S.); +1(615) 385-1100 ext. 274 (international).

Cable Ties AreStrong and

Corrosion Resistant

Nelco Self-Lock Stainless SteelCable Ties are designed for use whererough weather, salt spray, extremevibration, radiation, chemical expo-sure and other hostile environmentsrequire a strong, durable cable tie,said the manufacturer.

The permanent ties feature 150-pound (68-kilogram) minimum looptensile strength; are 3/16 inch (in.; 0.48centimeter [cm]) wide by 0.01 in. (0.03cm) thick; and are available in sizes

ranging from five in. (12.7 cm) longto 47 in. (119 cm) long.

For more information: Nelco Prod-ucts, 22 Riverside Dr., Pembroke,MA 02359 U.S. Telephone (800)346-3526 (U.S.); +1(781) 826-3010(international).

Diagnostic DeviceAids Detection of

Intermittent DefectsIn Avionics

The IFD-2000 Intermittent FaultDetector simultaneously and con-tinuously monitors hundreds oflines to detect and diagnose intermit-tent defects in electronic circuitboards and related equipment, saidthe manufacturer. The device is acomputer-operated tester-analyzerthat employs a proprietary “frontend” hardware neural network toperform real-time data reductionwith sensor-fusion techniques. Thebasic unit monitors up to 256 single-ended lines, and can be expanded to4,096 test points/input lines withadditional modules.

Because the device tests all linessimultaneously and continuously, itcan identify small or short-durationintermittent failures. The device’ssensitivity is programmable to detectohmic events as low as 20 ohms andwide-open intermittents as short as130 nanoseconds in duration.

Nelco Self-Lock StainlessSteel Cable Tie


For more information: UniversalSynaptics, 1801 W. 21st Street,Ogden, UT 84401 U.S. Telephone+1(801) 731-8508.

Aviation DegreeOn-line

The University of Nebraska at Oma-ha Aviation Institute and College ofContinuing Studies are offering an In-ternet-based aviation studies degree.Students can complete from 24 to 30hours of aviation studies coursework, and these courses can be com-bined with other academic and non-traditional credit to complete therequirements for a bachelor’s degreewith a concentration in aviationstudies.

For more information: AviationInstitute, Allwine Hall 422, Univer-sity of Nebraska at Omaha, Omaha,NE 68182-0508 U.S. Telephone(800) 335-9866 (U.S.); +1(402)595-2342 (international).

Backup RingProtects Elastomeric

Components

The Split-Lock™ Backup Ring fromGreene, Tweed & Co. is designedfor field-maintenance technicians whohave experienced difficulty assem-bling multipiece split backup-ring

components in aircraft landing gear,said the manufacturer.

Under field-maintenance conditions,the ring halves can be articulatedaround the circumference to allow thecut ends to meet. This articulation re-sults in the unit assembly opening asa conventional scarf-cut backup ring.

For more information: Greene, Tweed& Co., Aerospace & Defense Group,1555 Bustard Rd., Suite 130, P.O. Box217, Kulpsville, PA 19443-0217 U.S.Telephone: +1(215) 256-9521.

Flexible GrindingDiscs Used for

Aluminum, Steel

Flexible grinding discs made of cot-ton fiber and impregnated with alu-minum oxide provide long service,said the manufacturer. Rex-Cut® Cut-N-Finish™ Discs are nonloading onaluminum and are also suitable foruse with mild steel and stainless steel.The discs are available in 24-, 36-,54-, and 80-grit sizes and come in 4.5-inch (11.4-centimeter) and seven-inch (18-centimeter) diameters.

For more information: Rex-Cut Prod-ucts, 960 Airport Road, P.O. Box2109, Fall River, MA 02722 U.S.Telephone: (800) 225-8182 (U.S.);+1(508) 678-1985 (international).♦

BLANKINSIDEBACK

COVER

Visit our World Wide Web site at http://www.flightsafety.org

�RIO November 8–11, 1999

Janeiro,Brazilde Janeiro,Brazilde

Enhancing Safety in the 21st CenturyEnhancing Safety in the 21st Century

International Air Transport AssociationFlight Safety Foundation

Hosted by

Embraer

Lider

TAM

Transbrasil

Varig

VASP

For information contact Ann Hill, tel. +1(703) 739-6700, ext. 105 or Ahlam Wahdan, ext. 102

A Joint Meeting of 52nd FSF annual International Air Safety Seminar, 29th IFA International Conference and IATA

International Federation of Airworthiness

may–june 1999 managing aircraft-tire w ear and damage ... · pdf filew ear and damage...

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