Aviation Mechanics Bulletin May-June 2002

MAY–JUNE 2002

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

MELs for Corporate andBusiness Aircraft GuideDeferred-maintenance

Decisions

SINCE 1947SINCE 1947

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

MELs for Corporate and Business Aircraft GuideDeferred-maintenance Decisions ..................................................................1

Maintenance Alerts ........................................................................................9

News & Tips ............................................................................................... 17

May–June 2002 Vol. 50 No. 3

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Cover: Darol V. Holsman, FSF manager of aviation safety audits, examines minimum equipmentlist documents for a Gulfstream IV. (FSF photo)

MELs for Corporate andBusiness Aircraft GuideDeferred-maintenance

Decisions

A minimum equipment list (MEL) provides a common basisfor maintenance technicians and pilots to determine whether

an aircraft can be operated safely — and legally — withinoperative instruments/equipment.

Robert A. Feeler

Minimum equipment lists (MELs)have been used for nearly 50 yearsby commercial aircraft operatorsthroughout the world; but corporate/business aircraft operators, which aregoverned by “general aviation” reg-ulations in many countries, are rela-tive newcomers to the use andapplication of the MEL concept.1

The International Civil Aviation Or-ganization (ICAO) defines an MELas “a list which provides for the op-eration of aircraft, subject to speci-fied conditions, with particular

equipment inoperative, prepared byan operator in conformity with, ormore restrictive than, the MMEL[master MEL] established for the air-craft type.”2

The MEL concept is described byICAO as follows:

The [MEL] is not intended toprovide for operation of the air-craft for an indefinite periodwith inoperative systems orequipment. The basic purposeof the [MEL] is to permit the

2 FLIGHT SAFETY FOUNDATION • AVIATION MECHANICS BULLETIN • MAY–JUNE 2002

safe operation of an aircraftwith inoperative systems orequipment within the frame-work of a controlled and soundprogram of repairs and parts re-placement.3

ICAO standards for commercial air-craft operators call for MELs to beincluded in the operations manual, sothat the pilot-in-command (PIC) can“determine whether a flight may becommenced or continued from anyintermediate stop should any instru-ment, equipment or systems becomeinoperative.”4

ICAO has not established standardsfor the use of MELs by general avia-tion aircraft operators. Nevertheless,several ICAO member countries havedeveloped such standards. For exam-ple, in North America, where nearly80 percent of worldwide corporate/business aircraft operators are locat-ed,5 regulations established by Trans-port Canada (TC) and the U.S.Federal Aviation Administration(FAA) include MEL provisions forgeneral aviation aircraft operators.

The provisions differ, in that commercial/business aircraft PICs in Canadamay use some discretion in determin-ing whether a flight can be conductedsafely with inoperative instruments/equipment.

Canadian Aviation Regulations(CARs) Part 605.08 says that “no

person shall conduct a takeoff in anaircraft that has equipment that is notserviceable or from which equip-ment has been removed if, in theopinion of the [PIC], aviation safetyis affected.”

The CARs require that the PIC of anaircraft for which an MEL has notbeen approved base his/her determi-nation of aircraft airworthiness onseveral factors, including:

• Equipment required by theCARs for the intended flight(e.g., day or night, visual flightrules or instrument flight rules);

• Equipment required by the air-craft manufacturer for the intend-ed flight; and,

• Requirements of airworthinessdirectives.6

In addition, any unserviceable equip-ment must be “isolated or secured”and placarded, and the PIC mustrecord the actions in the aircraft log-book.

The CARs require that, if an MEL hasbeen approved for the aircraft, thePIC’s determination of aircraft air-worthiness must be based also on theconditions or limitations specified inthe MEL.7

In the United States, Federal AviationRegulations (FARs) Part 91 prohib-its general aviation aircraft operators

FLIGHT SAFETY FOUNDATION • AVIATION MECHANICS BULLETIN • MAY–JUNE 2002 3

from conducting a takeoff in an air-craft that has any inoperative instru-ments or equipment unless theoperation is conducted under theprovisions of an MEL.8 (The regula-tion includes exceptions for specificequipment aboard specific aircraft,such as rotorcraft and small, non-turbine-powered airplanes.)

For U.S. operators, proper use of anapproved MEL enhances operationalflexibility because an aircraft cancontinue to be flown, under specificconditions and for a limited time, withcertain instruments/equipment inop-erative.

Another benefit, especially for opera-tors of complex multi-engine aircraftand/or turbine aircraft, is that an MELensures that those involved in the op-eration of the aircraft use the same in-formation to evaluate a malfunctionand its effect on continued operations.An MEL assists pilots, as well asmaintenance technicians, in determin-ing what is safe, logical and legal.

(An MEL also assists an operator indocumenting aircraft airworthiness toensure that insurance coverage re-mains valid. There have been instanc-es in which an aircraft was damagedas a result of something that was notrelated to inoperative equipment,such as a landing light; nevertheless,because the operator failed to docu-ment approved continued operationunder the provisions of an MEL, the

insurance company ruled that the op-erator had failed to maintain the air-craft in airworthy condition anddeemed the insurance invalid.)

The FAA, in Advisory Circular (AC)91-67, defines MEL as follows:

The MEL is the specific inoper-ative equipment document for aparticular make and model air-craft by serial and registrationnumbers (e.g., BE-200 [BeechSuper King Air 200], N12345).A [FARs] Part 91 MEL consistsof the MMEL for a particulartype aircraft, the preamble forPart 91 operations, the proce-dures document and a LOA [let-ter of authorization]. The FAAconsiders the MEL as an STC[supplemental type certificate].As such, the MEL permits op-eration of the aircraft underspecified conditions with certainequipment inoperative.9

MMEL is defined in AC 91-67 as fol-lows:

An MMEL contains a list ofitems of equipment and instru-ments that may be inoperativeon a specific type of aircraft(e.g., BE-200 …). It is also thebasis for the development of anindividual operator’s MEL.

An MMEL typically is developed aspart of the aircraft-certification process:


An aircraft undergoes initial flight-testing before issuance of a type certif-icate and a production certificate un-der the auspices of an FAA AircraftEvaluation Group (AEG). Although themanufacturer conducts the testing andprovides most of the engineering talent,it does so under the direction of the AEG.

As the certification process nears com-pletion, a group of FAA engineers,FAA pilots and FAA technicians isconvened as the Flight OperationsEvaluation Board (FOEB). The man-ufacturer, prospective customers/operators of the aircraft and othersmay assist the FOEB, but the FOEBhas final authority over the certification-approval process and the issuance ofthe aircraft flight manual (AFM).

The FOEB also evaluates proposalssubmitted by the manufacturer and byprospective operators for items to beincluded on the MMEL. Althoughmany people may be involved in datacollection and evaluation, the FOEBhas sole authority for deciding whatgoes into the MMEL.

Copies of approved MMELs areavailable from FAA flight standardsdistrict offices (FSDOs) or from theFAA Web site at <www.faa.gov/fsdo/abq/mmel.html>. MMELs are avail-able from other sources, includingaircraft manufacturers; nevertheless,the only authorized (and legal)MMELs are those produced and dis-tributed by FAA.

The meaning of the term inoperative,as used in the context of the FARs,must be understood clearly. AC91-67, as well as the preamble of ev-ery Part 91 MEL, says:

Inoperative means that a systemand/or component has malfunc-tioned to the extent that it doesnot accomplish its intendedpurpose and/or is not consis-tently functioning normallywithin its approved operatinglimits or tolerances.

By this definition, an indicator report-ed as “fluctuating,” a component re-ported as “intermittent” or a gaugereported as “sticking” must be con-sidered inoperative. The malfunctionmust be corrected by a maintenancetechnician, or — if an MEL autho-rizes continued operation of the air-craft with the inoperative equipment— the operator must comply withspecific instructions in the MEL forthat equipment (e.g., placarding theequipment as inoperative, conductingmaintenance/operational proceduresand entering information in the air-craft maintenance records).

A logbook entry stating “could notduplicate on ground” is not a satis-factory response to a pilot report ofan equipment malfunction that fits thedefinition of inoperative.

Provisions for the use of MELs by Part91 operators were adopted by FAA in


1988, in response to petitions forexemptions from several corporateaviation departments with air carrier-type aircraft. In 1991, FAA issued AC91-67, which discusses the MEL con-cept and provides guidance for operat-ing with an MEL or without an MEL.

The advisory circular discusses theFAA’s MEL-approval process step bystep. Other sources of information arethe General Aviation Operations In-spector’s Handbook (FAA Order8700.1, Chapter 58) and the GeneralAviation Airworthiness Inspector’sHandbook (FAA Order 8300.10,Chapter 37). The handbooks discusshow FSDO inspectors process MELrequests.

The first step in applying for an MELis to call the FSDO that has jurisdic-tion over the area in which the aircraftis based and request an appointmentfor a meeting. During the first meet-ing, the applicant likely will discussthe approval process, regulatory re-quirements and other issues with sev-eral inspectors (specializing inoperations, airworthiness and avion-ics); one inspector will be assigned bythe FSDO supervisor to work with theapplicant as the process continues.

Before issuing a LOA that authoriz-es the operator to use the MMEL asthe MEL for its aircraft, FSDO in-spectors will discuss requirements forthe procedures document with theoperator. Nevertheless, the operator

solely is responsible for preparing thedocument. AC 91-67 includes the fol-lowing guidance:

The operator should developthe [procedures document] us-ing guidance contained in themanufacturer’s aircraft flight[manual] and/or maintenancemanual, the manufacturer’s rec-ommendations, engineeringspecifications and other appro-priate sources. The operatormay consult FSDO airworthi-ness inspectors for advice orclarification, but the operator isresponsible for preparing thedocument.

Although FAA does not review orapprove the procedures document, aramp check or an incident investiga-tion may result in enforcement actionif the operator fails to prepare thedocument or does so incorrectly.(This is one reason that some opera-tors hire consultants who specializein developing aircraft-specific MELsand procedures documents.)

The procedures document includessupplementary information that is usedin conjunction with the MEL. Descrip-tions of requirements for some itemson an MEL are self-explanatory. Forexample, the BE-200 MMEL says thatone static wick is allowed to be miss-ing or broken on each wing, on eachside of the horizontal stabilizer and onthe vertical stabilizer.


The descriptions of requirements forother items on an MEL, however, in-clude the following notations: “(M)” —meaning that a specific maintenanceprocedure must be conducted; “(O)” —meaning that a specific operations pro-cedure must be conducted; and “asrequired by FAR” — meaning thatthe FARs have specific requirementsor limitations for operation of the item.

Details on the maintenance proce-dures, operating procedures and FARsrequirements/limitations must be in-cluded in the procedures document.Where appropriate, the proceduresdocument should provide specific ref-erences to sections of the aircraft main-tenance manual or the AFM.

For example, the BE-200 MMEL in-cludes the following description ofrequirements for the electric elevator-trim system: “(M) May be inopera-tive provided [that] manual trim isunaffected.” The notation “(M)” in-dicates that the procedures documentincludes a maintenance procedure forensuring that operation of the manu-al elevator-trim system is not affect-ed by the malfunction of the electricelevator-trim system.

After receiving approval to operatewith an MEL, the operator is respon-sible for keeping the MEL and theprocedures document up-to-date.

The FOEB for each aircraft type meetsperiodically to review the MMEL and

to consider revisions suggested by oth-ers within the FAA (e.g., FSDO in-spectors), by the manufacturer and byoperators. The meetings typically oc-cur frequently after an aircraft is cer-tified and become less frequent as theaircraft accumulates time in service.

Section 22 of AC 91-67 describeshow an operator can submit a peti-tion to the FSDO to have newly in-stalled equipment added to theMMEL. One important but often-overlooked provision is that an oper-ator who petitions FAA for an MMELrevision is permitted to operate theaircraft with that equipment added tothe MEL while the FSDO, the FOEBand possibly the AEG consider therequested MMEL revision. Until theFAA acts on the petition, the operatorcan treat the item as if it were on theMMEL and develop operations-and-maintenance procedures as appropriate.

When a FSDO issues a LOA, theFSDO adds information about the op-erator and the operator’s aircraft to amaster list of authorized MEL opera-tors. The master list is maintained atthe FAA’s Mike Monroney Aeronau-tical Center in Oklahoma City, Okla-homa. When an MMEL is revised, thecenter mails postcards to the affectedoperators, notifying them of the revi-sion and advising that they have 30days to incorporate the revision in theirMELs and to include necessary infor-mation in their procedures documents.The operators can obtain copies of


revised MMELs from their FSDOs orfrom the FAA Web site.

Because the operator solely is respon-sible for ensuring that its MEL is up-to-date, the operator should confirmwith the FSDO that the company andall the aircraft for which it has obtainedMEL approval are included on themaster list. Periodic checks of MMELrevision status on the FAA Web sitealso are prudent; the site includes a listthat shows the revision number andrevision date for each MMEL.

The requirements for when inopera-tive equipment must be repaired dif-fer for commercial operators andgeneral aviation operators. Each itemon an MMEL is assigned a repair cat-egory; the repair categories applyonly to commercial operators. Forexample, a Category A item must berepaired according to the time inter-val specified by the MEL in the re-marks section for that item. ACategory B item must be repairedwithin three days; a Category C itemwithin 10 days, and a Category Ditem within 120 days.

Compliance with the requirements ofthe repair categories is not mandato-ry for Part 91 operators. Instead, thepreamble to each MMEL contains thefollowing guidance for general avia-tion operators:

The MMEL is intended to per-mit operations with inoperative

items of equipment for the min-imum period of time necessaryuntil repairs can be accom-plished. It is important that re-pairs be accomplished at theearliest opportunity in order toreturn the aircraft to its designlevel of safety and reliability.Inoperative equipment in allcases must be repaired, or in-spected and deferred, by quali-fied maintenance personnel atthe next required inspection.

The preamble also says that whenequipment is found to be inoperative,an entry must be made in the aircraftmaintenance records to show wheth-er the equipment was repaired or therepair was deferred in accordancewith the MEL.

Operating under the provisions of anMEL requires some effort. Neverthe-less, the effort likely will be reward-ed when a Part 91 aircraft, whichotherwise would be grounded be-cause of inoperative equipment, cancontinue to be operated — albeit tem-porarily — under the provisions of anMEL.♦

Notes1. The National Business Aviation

Association (NBAA), in NBAABusiness Aviation Fact Book2002, said, “The terms businessaircraft and corporate aircraftoften are used interchangeably


because they both refer to an air-craft used to support a businessenterprise.” NBAA said that theU.S. Federal Aviation Adminis-tration (FAA) defines businesstransportation as “any use of anaircraft (not for compensation orhire) by an individual for trans-portation required by the busi-ness in which the individual isengaged.” NBAA said that FAAdefines corporate/executivetransportation as “any use of anaircraft by a corporation, com-pany or other organization (notfor compensation or hire) for thepurposes of transporting its em-ployees and/or property, andemploying professional pilots forthe operation of the aircraft.”

2. International Civil Aviation Or-ganization (ICAO). InternationalStandards and RecommendedPractices (SARPS). Annex 6 tothe Convention on InternationalCivil Aviation: Part I, Interna-tional Commercial Air Transport— Aeroplanes. Chapter 1, “Defi-nitions.”

3. ICAO. SARPS. Annex 6: Part 1.Attachment G, “MinimumEquipment List (MEL).”

4. ICAO SARPS. Annex 6: Part I.Chapter 6, “Aeroplane Instru-ments, Equipment and FlightDocuments,” 6.1.2.

5. NBAA. NBAA Business AviationFact Book 2002: 21.

6. Transport Canada (TC). CivilAviation Regulations (CARs)Part VI, General Operating andFlight Rules. Subpart 5, AircraftRequirements. Part 605.10, “Un-serviceable and Removed Equip-ment — Aircraft Without aMinimum Equipment List.”

7. TC. CARs Part VI. Subpart 5.Part 605.09, “Unserviceable andRemoved Equipment — AircraftWith a Minimum EquipmentList.”

8. FAA. Federal Aviation Regula-tions Part 91, General Operatingand Flight Rules. Part 91.213,“Inoperative Instruments andEquipment.”

9. FAA. Advisory Circular 91-67,Minimum Equipment Require-ments for General Aviation Op-erations Under FAR Part 91.June 28, 1991.

About the Author

Robert A. Feeler has been a certifiedaircraft maintenance technician since1952 and has served in senior man-agement positions at two U.S. air-lines. A frequent contributor toAviation Mechanics Bulletin, he wasappointed editorial coordinator of thepublication in 1991. Feeler alsoserved as manager of Flight SafetyFoundation (FSF) safety audit pro-grams from 1992 through 1999, whenhe participated in developing the FSF


FAA RecommendsInspections of JT8D-200

High-pressureCompressor Front Hubs

The U.S. Federal Aviation Adminis-tration (FAA) has recommendedinspections of Pratt & Whitney JT8D-200 series high-pressure compressor(HPC) front (C-8) hubs because crackshave been found on some hubs.

In a special airworthiness informationbulletin (NE-02-22) issued March 26,

2002, FAA said that cracks have beenfound on 16 hubs at the interface ofthe C-8 hub and the stage 8 to stage 9spacer.

“The cause of the cracking appearsto be fretting-induced fatigue,” FAAsaid. “The fretting is believed to bethe result of spalling [the breaking offof surface material caused by inter-nal stress] of the PWA-110 coatingin the spacer-hub interface as a resultof normal relative motion between thehub and the spacer. The spalled coat-ing material, trapped between the hub

Q-Star Charter Provider VerificationProgram and was appointed programadministrator.

Further Reading FromFSF Publications

FSF Editorial Staff. “MEL RevisedAfter Depressurization Incident.”Flight Safety Digest Volume 20 (July2001): 21–22.

Arbon, E.R.; Mouden, L. Homer;Feeler, Robert A. “The Practice ofAviation Safety.” Flight Safety DigestVolume 20 (June 2001): 18–19.

Hessburg, Jack. “Analysis of Airwor-thiness Describes Conformity, Safety

as Key Elements.” Aviation Mechan-ics Bulletin Volume 48 (March–April2000).

FSF Editorial Staff. “Learjet StrikesTerrain When Crew Tracks FalseGlideslope Indication and ContinuesDescent Below Published DecisionHeight.” Accident Prevention Volume56 (June 1999).

FSF Editorial Staff. “Faulty Instru-ment, Poor Judgment Bring DownConvair Turboprop.” Accident Pre-vention Volume 49 (July 1992).

Pope, John A. “Special Inspection ofCommuters.” Accident PreventionVolume 46 (August 1989).

MAINTENANCE ALERTS


and spacer, produces high contactstresses [that] result in the frettingand, ultimately, cracking of the hub.”

In each instance, cracks have beenfound on configurations in whichPWA-110 coating has been used on thespacer and nickel cadmium coatinghas been used on the hub (the config-uration used since 1987 in productionof JT8D-217C and JT2D-219 HPCs).

The cracks typically have been foundon HPCs with more than 13,000 cy-cles in service since new or since thelast HPC overhaul.

“The cracks appear in the aft face ofthe hub between the 9 [o’clock] to 11o’clock [position] and 1 [o’clock] to3 o’clock position adjacent to the tie-rod holes,” FAA said. “The clock po-sition on the tie-rod hole is definedby viewing the hub from the aft fac-ing forward with 12 o’clock locatedon the tie-rod hole circumferencenearest the OD [outside diameter] ofthe hub.”

FAA said that a related field manage-ment plan would be developed andincorporated into an airworthinessdirective (AD). Until the AD is is-sued, FAA recommended that opera-tors, repair stations and principalmaintenance inspectors take the fol-lowing actions:

• Perform a full compressor over-haul, at the next engine-shop visit,

of engines with high-risk crite-ria and develop a schedule forearly removal of the highest-timeengines;

• Review current C-8 hub fluores-cent magnetic particle inspection(FMPI) techniques to ensure thatthey establish the correct mag-netic field for detecting cracks inthe areas identified as suscepti-ble to cracking;

• Implement focused visual in-spections and FMPI inspectionsof the susceptible areas;

• Report inspection findings to themanufacturer; and,

• Be aware of further manufactur-er recommendations.

Open Cowl DoorSeparates From A320

Engine Nacelle, StrikesHorizontal Stabilizer

An Airbus A320 was acceleratingthrough takeoff rotation speed (VR)at McCarran (Las Vegas, Nevada,U.S.) International Airport when theoutboard forward cowl door on theno. 1 (left) engine separated from theengine nacelle and struck the horizon-tal stabilizer. The flight crew flew theairplane to the departure airport andconducted a normal landing. The air-plane received minor damage; noneof the 152 people in the airplane wasinjured.


The U.S. National TransportationSafety Board, in its final accidentreport, said that the probable causeof the accident was “the failure ofthe mechanic to refasten the cowlingdoor prior to returning the aircraft toservice.”

An investigation revealed that thecowl door had separated from theengine nacelle and that there were a10-inch (25-centimeter) cut in thelanding-gear door and three holes inthe lower surface of the left horizon-tal stabilizer. Each hole was about twoinches (5.1 centimeters) wide andeight inches (20 centimeters) long.The report said that the cowling-door“hold-open rod” had penetrated thelower skin and spar web of the hori-zontal stabilizer. The opposite (in-board) cowl door and the area wherethe two doors hinge were damagedbut remained attached to the enginenacelle. The cowl door “over-center”latches on the inboard door werelatched, and the hooks were intact andundamaged. On the outboard door,the latch receptacles — which werepainted red — also were undamaged.

The report said that the flight was thefirst after maintenance personnel hadconducted a remain-overnight checkthe previous night.

The accident report said that thecheck had been conducted “duringhours of darkness. The … check re-quired that the cowling doors be

opened; however, the mechanic per-forming the work reported that thecowl doors were closed and re-latched about 0530–0600 duringhours of daylight. In the morning, theaircraft was handed over from themaintenance graveyard [overnight]shift to the day shift. Maintenanceitems remained to be completed inareas of the aircraft other than the no.1 engine. The takeoff [in which] thecowing separated was the first flightfollowing return to service.”

Under-reporting ofR22 Flight Time

Cited in Failure ofMain-rotor Blade

A Robinson R22 Beta helicopter wasbeing flown in a cattle-herding oper-ation in Australia when, at 200 feetabove ground level, the helicopterdeveloped a lateral vibration. The pi-lot lost control of the helicopter,which then struck the ground. Thehelicopter was destroyed; the pilotreceived fatal injuries, and a passen-ger received serious injuries.

The Australian Transport Safety Bu-reau (ATSB) said, in its final reporton the July 29, 2000, accident, thatthe main-rotor mast assembly sepa-rated in flight, damaging the enginefirewall and the two fuel tanks. Onemain-rotor blade separated from themain-rotor hub. The blade, whichfractured at the blade-root fitting, was


found 105 meters (345 feet) from theaccident site. ATSB said that the fail-ure resembled a 1990 accident inwhich a blade on an R22 helicopterused in herding operations had ex-ceeded its service life. Investigationof the 1990 accident revealed thatthere had been a fatigue crack in themain-rotor-blade root fitting and thatthe main-rotor blade had exceeded itsretirement time by at least 257.2 op-erating hours. (In that accident, au-thorities said that the hours recordedin the helicopter logbook apparentlywere not the helicopter’s actual op-erating hours and that there was amanufacturing anomaly in the main-rotor blade that related to load trans-fer through the rib-root fitting. Afterthe accident, the manufacturer tookaction to eliminate the anomaly.)

ATSB said in its report on the 2000accident that the helicopter’s hourmeter showed that the helicopter had2,124.6 hours total time in service(TIS). The last recorded maintenancewas a 100-hour inspection completed25 days before the accident; mainte-nance records said that the helicopterwas released to service at 2,102.4hours. No flight entries were record-ed after the inspection. The ATSB saidthat its review of helicopter records“suggested [that] the helicopter oper-ating hours were being under-reported.”The report said that the pilot’s logbookshowed that, in the 90 days before theaccident, the pilot had flown the acci-dent helicopter for 95.6 hours.

The recorded TIS of the separatedmain-rotor blade (part no. A016-2)was 1,995.5 hours; the logbook saidthat the blade had accumulated1,299.9 hours TIS when it was in-stalled in the accident helicopter morethan two years before the accident.The manufacturer said that the man-datory retirement time of the main-rotor blade was 2,200 hours TIS.

“The under-reporting of helicopterflight time probably resulted in anactual service life of the failed mainrotor blade in excess of the manu-facturer’s stated limits,” the reportsaid. “There has been a history of …failures of the R22 main-rotor bladeduring its evolution. Those eventshave led to a series of modificationsto address the anomalies discovered.Exceeding the service life of a dy-namic component such as a main-rotor blade will exacerbate thepossibility of undetected catastroph-ic component failure.”

Excessive Grease onBrush Seals Suspected

in Loss of AileronControl

A Learjet 35A was being flown on anemergency medical services flight inBritish Columbia, Canada, from Van-couver to Terrace. After takeoff, whilebeing flown through Flight Level 290(approximately 29,000 feet) with theautopilot engaged, the aircraft turned


right with five degrees of bank. Theflight crew disengaged the autopilotand tried to stop the right turn, but theailerons could not be moved.

The incident report by the Transpor-tation Safety Board of Canada (TSB)said that, as the flight crew used var-ious control inputs to try to move theailerons, the bank angle increased toabout 20 degrees. Then, as the crewapplied force to the ailerons, full ai-leron control returned.

An investigation revealed that the air-plane had been parked outdoors forseveral hours during a heavy rain witha surface temperature of 8 degreesCelsius (46 degrees Fahrenheit). Thefreezing level was 5,000 feet.

“Because of the nature of the malfunc-tion and the environmental conditions,and because the malfunction clearedup in the air, freezing of the controlswas suspected,” the report said. “Theaileron brush seals were examined by[the operator’s] maintenance person-nel shortly after the aircraft landed.Excessive amounts of water and trac-es of ice were observed in the brushseals. The seals were cleaned, driedand relubricated. The aircraft was re-examined two days after the incident;the brush seals were visibly worn andmatted, and some of the drainagechannels were distorted.”

The report said that a review of ser-vice difficulty reports and information

from the manufacturer revealed thatsimilar incidents of Learjet aileron-control problems occur about once ayear. In each occurrence, the airplanewas “thoroughly soaked” with water,then was flown into freezing temper-atures; in every occurrence the sus-pected cause of the problem wasfrozen aileron brush seals. (Brush sealsare installed to prevent aileron buzz athigh speeds.)

When brush seals are worn and mat-ted, drainage channels in the brushseals — located about every inch (2.5centimeters) — no longer allow pas-sage of water.

The operator’s maintenance proce-dures called for the seals to be“cleaned with a dry, clean cloth andthen lubricated with a silicone-basedgrease every 300 hours,” the reportsaid. “The practice was to be gener-ous with the grease.”

The report said that the Learjet 35Amaintenance manual said that greas-ing should not be excessive becausetoo much grease can block the drain-age channels; nevertheless, the man-ual did not say how much grease wasconsidered excessive and did not es-tablish criteria for replacing wornseals or damaged seals.

As a result of the occurrence, theoperator reduced the lubrication in-terval from 300 flight hours to 100flight hours and the manufacturer was


revising maintenance manuals for allLearjet airplanes to include morecomplete lubrication instructions andinspection criteria for worn brushseals or damaged brush seals.

Blocked Wheel-wellDrain Lines Blamed forAileron-control Problem

A Boeing 767-200 was in cruise atFlight Level 390 (approximately39,000 feet) on a transcontinentalflight in the United States from NewYork, New York, to San Francisco,California. The center autopilot andthe autothrottles were engaged. Thecaptain said that the autopilot madean uncommanded disconnect.

The final accident report by the U.S.National Transportation Safety Board(NTSB) quoted the captain as sayingthat when he took control of the air-plane, “the control wheel wasjammed in the straight-and-level po-sition.” About 15 pounds (6.8 kilo-grams) of force was applied to freethe control wheel. The flight crewdeclared an emergency and divertedthe flight to Chicago (Illinois) O’HareAirport, where a normal landing wasmade. The autopilot and autothrottleswere not engaged for the remainderof the trip.

The initial examination of the air-plane revealed no anomalies relatedto the aileron-control problem. A

subsequent inspection, however, re-vealed debris obstructing the wheel-well canted-pressure deck-drain lines.

The report said that Boeing ServiceBulletin (SB) 767-51A0020 had rec-ommended changes in the drain sys-tem to “help ensure that fluid enteringthe canted-pressure-deck area will bedrained out of the airplane and notleak into the wheel-well area, whereit could freeze on the aileron-controlcables or the landing-gear doors dur-ing flight.”

Before the SB was issued, three op-erators had reported accumulations ofice on the aileron-control cables.

The SB said, “In two of the instanc-es, the ice on the aileron cables causedthe control wheel not to move whenon autopilot. The autopilot was dis-engaged, and the pilot had to operatethe aileron system manually. Higher-than-normal control-wheel-inputforce was required to free the cablesand restore normal aileron control.The ice buildup on the aileron-control cables was attributed to fluidfrom the sloping pressure deck leak-ing into the wheel well and freezing.”

The incident report said that thechanges in the drain system describedin the service bulletin had not beenimplemented on the incident airplane.Rain had been reported in New Yorkfor several hours before the airplane’sdeparture.


Faulty InstallationCited in In-flight

Propeller Separation

On July 25, 2000, about 80 minutesafter departure from Destin–FortWalton Beach Airport in Destin,Florida, U.S., the pilot of a Cessna421A Golden Eagle in cruise flightat 12,000 feet felt a slight vibrationand observed the right propeller sep-arate from the airplane. The pilotdeclared an emergency and divertedthe flight to Jackson (Mississippi,U.S.) International Airport, where heconducted an uneventful landing.The six people in the airplane werenot injured.

An inspection of the airplane by aU.S. Federal Aviation Administrationairworthiness inspector revealed thatthe right propeller assembly had sep-arated completely from the engine.(The propeller assembly was foundmore than three months after the ac-cident.) The inspection also revealedthat the upper surface of the leadingedge of the right horizontal stabilizerhad been crushed, that the outboardsection of the horizontal stabilizer hadbeen displaced about 35 degreesdown and that there were compres-sion wrinkles on the bottom skin ofthe right horizontal stabilizer. Therewas a hole in the top of the crankcaseof the right engine, and five fracturedstuds were found in the engine com-partment area. Nuts were attached to

all five studs, and spacers were at-tached to three studs; three other spac-ers had separated from the nuts butwere found in the engine compart-ment area.

“Examination of the fracture surfaceof the no. 1 propeller [assembly] re-vealed features typical of overstressseparation,” the U.S. National Trans-portation Safety Board said in the fi-nal accident report. “Crack arrestlines indicative of fatigue cracking[were] noted on all the fracture sur-faces of all eight [propeller-mounting]studs. Contact damage and deforma-tion [were] noted to the end of all thespacers adjacent to the mountingflange of the propeller gear. Four ofthe recovered seven spacers werelater determined to be damaged,which shortened their length to lessthan the specified length. Only twoof the eight fractured studs … extend-ed the minimum distance beyond thenut specified by McCauley PropellerSystems.”

The report said that an annual inspec-tion had been conducted on the air-plane on Jan. 5, 2000, and that bothpropellers had been removed duringthe annual inspection for compliancewith an airworthiness directive. Thepropellers later were replaced for eco-nomic reasons, the report said.

“At the time the mechanic signedoff the annual inspection, neitherpropeller was installed,” the report


said. “An entry in the right-enginelogbook with the same date as theannual inspection indicates that a‘zero-time’ propeller was installed.The replacement propellers wereoverhauled on Feb. 3, 2000, and in-stalled by a mechanic other than themechanic who performed the annu-al inspection on an unknown dateafter overhaul.”

At the time of the accident, the air-plane had accumulated about 50flight hours since installation of theright propeller.

The report said that the probablecause of the accident was the “inade-quate installation of the right propel-ler by the mechanic for his failure toproperly torque the eight nuts, result-ing in fatigue failure of the studs andseparation of the right propeller.” Theinvestigation also found that the me-chanic used uncalibrated torquewrenches and an outdated servicemanual.

Noncompliance WithAD Cited in Engine

Failure

A Piper PA-31-350 Chieftain wasbeing flown in cruise flight nearBoulder City, Nevada, U.S., on July23, 2000, when the pilot of the on-demand passenger flight heard a loudpopping sound and observed a surgein the left engine.

The pilot flew the airplane towardlower terrain, intending to land theairplane at the closest airstrip. Hisattempts to restart the engine failed,and he conducted checklists to shutdown the engine and feather the pro-peller. With one engine operative, theairplane did not maintain altitude, andthe pilot conducted an emergencylanding on a beach at Lake MeadNational Recreation Area. During therollout, the airplane struck rocks andthe nose landing gear and the left-main landing gear collapsed. The pi-lot and nine passengers were notinjured.

An inspection of the left engine re-vealed a fractured fuel-injector linefor the no. 6 cylinder injector nozzle.When the fractured fuel-injector linewas replaced with a serviceablefuel-injector line and the engine wasoperated, the engine met all specifi-cations. The inspection revealed nosupport clamps on the fuel-injectorline between the manifold and theinjector nozzle. Support clamps werefound on injector lines to the five oth-er cylinders.

The operator said that the enginehad been inspected July 14, 2000,23 operating hours before theaccident.

The accident report by the U.S. Na-tional Transportation Safety Boardsaid that Airworthiness Directive(AD) 93-02-05 had been issued June


NEWS & TIPS

Castellated LocknutsProduced in Variety of

Materials, Finishes

SPS Technologies castellated lock-nuts are available in hex configura-tion and 12-point configuration, in avariety of materials and finishes foruse in commercial aircraft and mili-tary aircraft and other applications,the manufacturer said.

The locknuts are available in sizesfrom 0.190 inch (4.826 millimeters)in diameter to two inches (51 milli-meters) in diameter and often areused with cotter pins for additionallocking assurance, the manufactur-er said.

For more information: SPS Technolo-gies, 301 Highland Ave., Jenkintown,PA 19046-2692 U.S. Telephone: +1(215) 572-3718.

Electric Drive SystemPowers Ground-support

Equipment

The Ecostar 80 V Electric Drive Sys-tem powers battery-operated airportbaggage-handling carts and battery-operated tugs, said the manufacturer,the Electric Drives Group of BallardPower Systems Electric Drives andPower Conversion Division.

14, 1993, to require compliance withTextron Lycoming Service Bulletin(SB) 342A. The AD and the SBrequired replacement of any fuel-injector line without clamps to sup-port the line at specific clampingpoints and repeated inspection of thefuel injector lines between the fuelmanifold and the injector nozzle to

Castellated Locknuts

detect cracks, dents or other indica-tors of unserviceable wear.

The report said that the probablecause of the accident was “the fatiguefracture and separation of the no. 6cylinder fuel-injector line due to thecompany maintenance personnel’sfailure to comply with an [AD].”♦


The Ecostar 80 V system includesan integrated drive-axle assembly,an 80-volt alternating current control-ler, a brake-pressure transducer, anelectronic accelerator pedal and anintegrated display gauge with abattery state-of-charge readout, themanufacturer said. A version of theEcostar 80 V system can drive con-ventional axles or power the pump inhydraulically driven systems, and adual-motor version can be used inhigher-power applications.

For more information: Ballard Pow-er Systems, 9000 Glenlyon Park-way, Burnaby, BC V5J 5J9 Canada.Telephone: +1 (313) 248-5395.

Portable Unit ProvidesTemporary Cooling

The Moving Cooler portable air-conditioning unit provides temp-orary cooling of aircraft maintenancefacilities and other areas, said themanufacturer, Skil-aire.

The Moving Cooler isolates the con-denser and evaporative air streamsto improve operating efficiency inproducing cooler air, which is direct-ed toward specific areas by two flex-ible cold-air outlets up to 10 inches(25 centimeters) in diameter and upto two feet (0.6 meter) long. Theunit, which operates on casters, canbe moved easily and fits throughstandard doorways. The Moving

Portable Air-conditioning Unit

Cooler is available in five coolingcapacities between one ton (0.9 met-ric ton) and five tons (4.5 metrictons).

For more information: Skil-aire, 1100Wicomico St., 6th Floor, Baltimore,MD 21230 U.S. Telephone: +1 (410)625-7545.

Software DiagnosesEquipment Faults

SmartSignal, a provider of equipment-condition-monitoring software, hasdeveloped the eCM 2.0 softwarepackage to detect and diagnose im-pending equipment faults before theequipment fails, the manufacturersaid.


The software provides early warn-ing information about deterioratingconditions in aircraft equipment, in-cluding bleed-valve leaks, high-pressure-turbine failures and high-pressure-compressor failures, en-abling operators to performpredictive maintenance. The soft-ware package also allows operatorsto incorporate into the software theirown information about engine-failure modes.

For more information: SmartSignal,4200 Commerce Court, Suite 102,Lisle, IL 60532 U.S. Telephone: +1(630) 245-9000.

Custom-built ToolsMeet Special Needs

Wright Tools has begun producingcustom-built hand tools developedaccording to customer specifications,the manufacturer said.

sketch, and provides informationabout the desired size, application,finish and torque.

For more information: Wright Tool,633 West Bagley Road, Berea, OH44017 U.S. Telephone: (800) 321-2902 (U.S.) or +1 (440) 234-1812.

Compact Reels PreventPower Cords From

Tangling

Shoreline Reels for power cords andhoses store up to 100 feet (31 meters)of cord or hose and prevent them frombecoming tangled, said the manufac-turer, TDI Products.

The reels, designed for use in aircrafthangars, are available in several

Compact Hose Reel

Custom-built Hand Tools

The hand tools are made after a cus-tomer completes a request form toprovide a description of the tool or a


versions to hold 50-amp power cords,30-amp power cords, 15-amp powercords and water-supply hoses. Thepower cords or hoses spool off thereels and can be retrieved using anelectrically powered motor.

For more information: TDI Products,740 South 10th St., Jacksonville, FL32250 U.S. Telephone: +1 (904) 242-0742.

Repair Kits RestoreDamaged Threads

Kato Fastening Systems’ thread-repairkits can be used to repair and overhaulstripped threads or damaged threadsusing helical coil inserts, the manufac-turer said.

The Kato-Kits are available in a vari-ety of sizes, and each kit includestanged inserts, a high-speed steelscrew thread insert (STI) tap and athreaded insertion tool.

For more information: Kato FasteningSystems, 11836 Fishing Point Drive,Suite 400, Newport News, VA 23606U.S. Telephone: +1 (757) 873-8980.

ThermoplasticMaterials Maintain

Critical Properties at AllTemperatures

Meldin polyimide and engineeredthermoplastic materials are available

in custom-molded machined compo-nents and stock shapes for machining,said the manufacturer, Saint-GobainPerformance Plastics.

Meldin Polyimide ThermoplasticMaterials

Meldin materials retain their criticalproperties at temperatures rangingfrom cryogenic to 600 degrees Fahr-enheit (F; 315 degrees Celsius [C])and may be used intermittently attemperatures as high as 900 degreesF (482 degrees C), the manufacturersaid. Meldin materials are strong,rigid and self-lubricating and haveapplications in many areas, includingaircraft and aerospace power systems.

For more information: Saint-GobainPerformance Plastics, 150 Dey Road,Wayne, NJ 07470-4699 U.S. Tele-phone: +1 (401) 253-2000.♦

Want more information about Flight Safety Foundation?

Contact Ann Hill, director, membership and development,by e-mail: [email protected] or by telephone: +1 (703) 739-6700, ext. 105.

Visit our Internet site at <www.flightsafety.org>.

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For more information, contact Robert Feeler, Q-Star program administrator,by e-mail: [email protected] or by telephone: +1 (410) 604-0004.

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