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P A R T1

Introduction

C h a p t e r

1Introduction

1.1 The aircraft engineering industry

The global aircraft industry encompasses a vastnetwork of companies working either as largeinternational conglomerates or as individualnational and regional organizations. The twobiggest international aircraft manufacturers arethe American owned Boeing Aircraft Com-pany and the European conglomerate, Euro-pean Aeronautic Defence and Space Company(EADS), which incorporates airbus industries.These, together with the American giantLockheed-Martin, BAE Systems and aerospacepropulsion companies, such as Rolls-Royce andPratt and Whitney, employ many thousandsof people and have annual turnovers totallingbillions of pounds. For example, the recentlywon Lockheed-Martin contract for the Amer-ican Joint Strike Fighter (JSF) is estimated tobe worth 200 billion dollars, over the next 10years! A substantial part of this contract willinvolve BAE Systems, Rolls-Royce and other UKcompanies.The airlines and armed forces of the world

who buy-in aircraft and services from aerospacemanufacturers are themselves, very often, largeorganizations. For example British Airways ourown national carrier, even after recent down-sizing, employs around 50,000 personnel. UKairlines, in the year 2000, employed in total,just over 12,000 aircraft maintenance and over-haul personnel. Even after the events that tookplace on 11th September 2001, the requirementfor maintenance personnel is unlikely to fall. Arecent survey by the Boeing Corporation expectsto see the demand for aircraft and their associ-ated components and systems rise by 2005, tothe level of orders that existed prior to the tragicevents of 11th September 2001.Apart from the airlines, individuals with

aircraft maintenance skills may be employedin general aviation (GA), third-party overhaul

companies, component manufacturers or air-frame and avionic repair organizations. GAcompanies and spin-off industries employ largenumbers of skilled aircraft fitters. TheUK armedforces collectively recruit around 1500 youngpeople annually for training in aircraft andassociated equipment maintenance activities.Aircraft maintenance certifying staff are

recognized throughout Europe and indeed,throughout many parts of the world, thusopportunities for employment are truly global!In the USA approximately 10,000 airframe andpropulsion (A&P) mechanics are trained annu-ally; these are the USA equivalent of our ownaircraft maintenance certifying mechanics andtechnicians.Recent surveys carried out for the UK sug-

gest that due to demographic trends, increasingdemand for air travel and the lack of trained air-craft engineers leaving our armed forces, thereexists an annual shortfall of around 800 suit-ably trained aircraft maintenance and overhaulstaff. Added to this, the global and diversenature of the aircraft maintenance industry, itcan be seen that aircraft maintenance engineer-ing offers an interesting and rewarding career,full of opportunity.

1.2 Differing job roles for aircraftmaintenance certifying staff

Individuals may enter the aircraft maintenanceindustry in a number of ways and perform avariety of maintenance activities on aircraft oron their associated equipments and components.The nature of the job roles and responsibilitiesfor licensed certifying mechanics, techniciansand engineers are detailed below.The routes and pathways to achieve these job

roles, the opportunities for career progression,the certification rights and the nature of the

4 Aircraft engineering principles

necessary examinations and qualifications aredetailed in the sections that follow.

1.2.1 The aircraft maintenancecertifying mechanic

Since the aircraft maintenance industry is highlyregulated, the opportunities to perform com-plex maintenance activities are dependent onthe amount of time that individuals spendon their initial and aircraft-type training, theknowledge they accrue and their length of expe-rience in post. Since the knowledge and experi-ence requirements are limited for the certifyingmechanic (see later), the types of maintenanceactivity that they may perform, are also lim-ited. Nevertheless, these maintenance activitiesrequire people with a sound basic education,who are able to demonstrate maturity and theability to think logically and quickly when act-ing under time constraints and other operationallimitations.The activities of the certifying mechanic

include the limited rectification of defects andthe capability to perform and certify minorscheduled line maintenance inspections, such asdaily checks. These rectification activities mightinclude tasks, such as a wheel change, replace-ment of a worn brake unit, navigation lightreplacement or a seat belt change. Scheduledmaintenance activities might include: replen-ishment of essential oils and lubricants, lubri-cation of components and mechanisms, paneland cowling removal and fit, replacement ofpanel fasteners, etc., in addition to the inspec-tion of components, control runs, fluid systemsand aircraft structures for security of attach-ment, corrosion, damage, leakage, chaffing,obstruction and general wear.All these maintenance activities require a

working knowledge of the systems and struc-tures being rectified or inspected. For example,to replenish the hydraulic oil reservoirs on amodern transport aircraft requires knowledgeof the particular system, the type of oil required(Figure 1.1), the replenishment equipment beingused, all related safety considerations andknowledge of the correct positioning of thehydraulic services prior to the replenishment.

Figure 1.1 Identification label showing the type ofoil contained within the drum.

Figure 1.2 Boeing 767 hydraulic reservoir chargingpoint, showing contents gauge, changeover valveand hydraulic hand pump.

In addition, for this task, the mechanic mustbe able to recognize the symptoms for internalor external hydraulic oil leakage when carryingout these replenishment activities on a particularhydraulic system reservoir.For example, Figure 1.2 shows the hydraulic

reservoir replenishing point for the Boeing767. The replenishment process requires thechangeover valve to be selected and oil suckedinto the reservoir, via the replenishment hose(Figure 1.3) which is placed in the oil container.The certifying mechanic then operates the handpump (see Figure 1.2) to draw the hydraulicfluid up into the reservoir. When the reservoir isfull, as indicated by the contents gauge, the hoseis withdrawn from the container, blanked andstowed. The changeover valve is put back intothe flight position, the panel is secured and the

Introduction 5

Figure 1.3 Hydraulic reservoir replenishmenthose, removed from stowage point.

appropriate documentation is completed by thecertifying mechanic, who will have a companyapproval to perform this task.For this job role, like all those that follow,

there is a statutory requirement for a particu-lar period of training and experience before amaintenance mechanic is issued with limitedcertifying privileges.Within the armed forces a similar job role

exists for those who have undergone training asaircraft mechanics, for flight line operations orsimilar maintenance activities.

1.2.2 The aircraft maintenancecategory B certifying technician

The role of the category B certifying technicianis subdivided into two major sectors: categoryB1 (mechanical) and category B2 (avionic). B1maintenance technicians will have an in depthknowledge of airframe, engine and electricalpower systems and equipment in addition to athorough knowledge of aircraft structures andmaterials. While category B2 maintenance tech-nicians will have an in-depth integrated knowl-edge of aircraft electrical, instrument, autopilot,radio, radar, communication and navigationsystems.The knowledge and skills gained from their

initial training, together with aircraft-typeknowledge and a substantial period of practicalexperience, will enable category B technicians,once granted approvals, to undertake one or

Figure 1.4 Boeing 767 flap drive motor and asso-ciated drive mechanism.

more of the following maintenance operations:

• In-depth scheduled inspection activities.• Complex rectification activities.• Fault diagnosis on aircraft systems, propul-sion units, plant and equipments.• Embodiment of modifications and specialtechnical instructions.• Airframe and other aircraft repairs.• Strip-down and aircraft re-build activities.• Major aircraft component removal, fit andreplacement tasks.• Use and interrogate built-in test equipment(BITE) and other diagnostic equipments.• Functional tests and checks on aircraft sys-tems, propulsion units and sub-systems.• Trouble-shooting activities on base and awayfrom base.• Aircraft engine ground running activities.• Rack and re-rack avionic equipments andcarry out operational tests and checks onavionic systems.• Supervise and certify the work of less experi-enced technicians and mechanics.

As can be seen from the above list of mainte-nance operations, the category B maintenancetechnician can be involved in a very wideand interesting range of possible activities. Forexample, Figure 1.4 shows a photograph ofthe Boeing 767 flap drive motor and associatedlinkage mechanism.The main source of power is via the hydraulic

motor, scheduled servicing may involve the


Figure 1.5 Technicians working at height consi-dering the alignment of the APU prior to fit.

operation and inspection of this complex sys-tem, which in turn requires the certifyingtechnician to not only have the appropriatesystem knowledge, but also the whole aircraftknowledge to ensure that other systems are notoperated inadvertently. Figure 1.5 shows twotechnicians working at height on highway stag-ing, considering the alignment of the aircraftauxiliary power unit (APU), prior to raising itinto position in the aircraft.To perform this kind of maintenance, to the

required standards, individuals need to demon-strate maturity, commitment, integrity and anability to see the job through, often underdifficult circumstances.Similar technician roles exist in the armed

forces, where the sub-categories are brokendown a little more into, mechanical, electrical/instrument and avionic technicians, as well asaircraft weapons specialists known as armamenttechnicians or weaponeers.In fact, it is planned from January 2004 that

the Royal Air Force (RAF) will begin initialtraining that follows the civil aviation trade cat-egories. That is mechanical technicians, whowill undertake airframe/engine training and to alesser extent electrical training and avionic tech-nicians, who will eventually cover all avionicsystems, in a similar manner to their civil coun-terparts. Cross-training of existing maintenancepersonnel is also planned to take place overthe next 10 years. The armament technician andweaponeer will still remain as a specialist tradegroup.

1.2.3 The base maintenancecategory C certifying engineer

Before detailing the job role of the category Clicensed engineer, it is worth clarifying themajordifferences in the roles performed by line main-tenance certifying staff and base maintenancecertifying staff. In the case of the former, theinspections, rectification and other associatedmaintenance activities take place on the aircraft,on the “live side” of an airfield. Thus the depthof maintenance performed by “linemaintenancepersonnel” is restricted to that accomplishablewith the limited tools, equipment and test appa-ratus available on site. It will include “first-linediagnostic maintenance”, as required.Base maintenance, as its name implies, takes

place at a designated base away from the live air-craft movement areas. The nature of the workundertaken on base maintenance sites will bemore in-depth than that usually associated withline maintenance and may include: in-depthstrip-down and inspection, the embodimentof complex modifications, major rectificationactivities, off-aircraft component overhaul andrepairs. These activities, by necessity, requirethe aircraft to be on the ground for longer peri-ods of time and will require the maintenancetechnicians to be conversant with a variety ofspecialist inspection techniques, appropriate tothe aircraft structure, system or componentsbeing worked-on.The category C certifier acts primarily in a

maintenance management role, controlling theprogress of base maintenance inspections andoverhauls. While the actual work detailed forthe inspection is carried out by category B tech-nicians and to a limited extent, category A basemaintenance mechanics, in accordance with thewritten procedures and work sheets. These indi-vidual activities are directly supervised by cate-gory B maintenance certifying technicians, whoare responsible for ensuring the adequacy ofthe work being carried out and the issuing ofthe appropriate certifications for the individualactivities.The category C certifier will upon completion

of all basemaintenance activities sign-off the air-craft as serviceable and fit for flight. This is doneusing a special form known as a certificate of

Introduction 7

Figure 1.6 Category C maintenance engineerexplaining the complexity of the technical log to theauthor.

release to service (CRS). Thus the category Ccertifying engineer has a very responsible job,which requires a sound all-round knowledge ofaircraft and their associated systems and majorcomponents (Figure 1.6). The CRS is ultimatelythe sole responsibility of the category C certify-ing engineer, who confirms by his/her signaturethat all required inspections, rectification, mod-ifications, component changes, airworthinessdirectives, special instructions, repairs and air-craft re-build activities have been carried outin accordance with the laid-down proceduresand that all documentation have been completedsatisfactorily, prior to releasing the aircraft forflight. Thus, the category C certifying engi-neer will often be the shift maintenance man-ager, responsible for the technicians and aircraftunder his/her control.The requirements for the issuing of an indi-

vidual category C licence and the education,training and experience necessary before theissue of such a licence are detailed in the sectionsthat follow.The military equivalent of the category C

licence holder will be an experienced main-tenance technician who holds at least seniornon-commissioned officer (SNCO) rank andhas a significant period of experience on air-craft type. These individuals are able to sign-offthe military equivalent of the CRS, for andon behalf of all trade technicians, who haveparticipated in the particular aircraft servicingactivities.

1.3 Opportunities for training,education and career progression

Those employed in civil aviation as aircraft cer-tifying staff may work for commercial aircraftcompanies or work in the field of GA. The leg-islation surrounding the training and educationof those employed in GA is somewhat differ-ent (but no less stringent) than those employedby passenger and freight carrying commercialairline companies. The opportunities and careerprogressions routes detailed below are primar-ily for those who are likely to be employedwith commercial carriers. However, they mayin the future, quite easily, be employed by GAorganizations.Commercial air transport activities are well

understood. In that companies are licensed tocarry fare paying passengers and freight, acrossnational and international regulated airspace.GA, on the other hand, is often misunderstoodfor what it is and what place it holds in thetotal aviation scene. Apart from including flyingfor personal pleasure, it covers medical flights,traffic surveys, pipeline inspections, businessaviation, civil search and rescue and other essen-tial activities, including pilot training! With theadvent of a significant increase in demand forbusiness aviation, it is likely that those who havebeen trained tomaintain large commercial trans-port aircraft will find increasing opportunity foremployment in the GA field.In the UK and indeed in many countries

that have adopted our methods for educat-ing and training prospective aircraft mainte-nance personnel. There have been, historically,a large number of different ways in whichthese personnel can obtain initial qualificationsand improver training. Since the advent of therecent Joint Aviation Requirements (JAR) legis-lation on personnel licensing, the methods forobtaining initial education and training havebecome somewhat more unified. Although therestill exist opportunities for the “self-starter”,achievement of the basic licensemay take longer.The schematic diagrams that follow are based

on those issued by the Civil Aviation Author-ity (CAA),1 Safety Regulation Group (SRG).They show the qualification and experience


routes/pathways for the various categories ofaircraft maintenance certifying staff, mentionedearlier.

1.3.1 Category A certifyingmechanics

JAR 147 approved training pathwayThe JAR 147 approved training organizationis able to offer ab initio (from the beginning)learning programmes that deliver JAR 66 basicknowledge and initial skills training that satisfythe regulatory authority criteria. In the case ofthe UK our regulatory authority is the CAA.

Figure 1.7 Category A qualifications and experience pathways.

Note that a list of CAA JAR 147 approvedtraining organizations, together with other use-ful education and training institutions, will befound in Appendix B, at the end of this book.Ab initio programmes in approved training

organizations often encompass the appropriateCAA examinations. If the examinations havebeen passed successfully, then an individualrequires 1 year of approvedmaintenance experi-ence before being able to apply for a category Aaircraft maintenance license (AML). Note alsothe minimum age criteria of 21 years, for allcertifying staff, irrespective of the category oflicense being issued (Figure 1.7).

Introduction 9

Skilled worker pathwayThe requirement of practical experience forthose entering the profession as non-aviationtechnical tradesmen is 2 years. This will enableaviation-orientated skills and knowledge to beacquired from individuals whowill already havethe necessary basic fitting skills needed for manyof the tasks likely to be encountered by thecategory A certifying mechanic.

Accepted military service pathwayExperienced line mechanics and base mainte-nance mechanics, with suitable military expe-rience on live aircraft and equipments, will havetheir practical experience requirement reducedto 6 months. This may change in the futurewhen armed forces personnel leave after beingcross-trained.

Category B2 AML pathwayThe skills and knowledge required by categoryA certifying mechanics is a sub-set of thoserequired by B1 mechanical certifying techni-cians. Much of this knowledge and many ofthe skills required for category A maintenancetasks are not relevant to the category B2 avioniccertifying technician. Therefore, in order thatthe category B2 person gains the necessary skillsand knowledge required for category A certifica-tion, 1 year of practical maintenance experienceis considered necessary.

Self-starter pathwayThis route is for individuals who may be takenon by smaller approved maintenance organiza-tions or be employed in GA, where companyapprovals can be issued on a task-by-task basis,as experience and knowledge are gained. Suchindividuals may already possess some generalaircraft knowledge and basic fitting skills by suc-cessfully completing a state funded educationprogramme. For example, the 2-year full-timediploma that leads to an aeronautical engineer-ing qualification (see Section 1.3.4).However, if these individuals have not prac-

ticed as a skill fitter in a related engineeringdiscipline, then it will be necessary to complete

the 3 years of practical experience applicable tothis mode of entry into the profession.

1.3.2 Category B certifyingtechnicians

The qualification and experience pathways forthe issue of category B1 and B2 AMLs areshown in Figures 1.8 and 1.9. Having discussedin some detail pathways 1–5 for the categoryA licence, it will not be necessary to providethe same detail for the category B pathways.Instead you should note the essential differencesbetween the category B1 and B2 pathways aswell as the increased experience periods requiredfor both, when compared with the category Alicense.Holders of the category A AML require a

number of years experience based on their back-ground. This is likely to be less for those wishingto transfer to a category B1 AML, rather thanto a B2 AML, because of the similarity in main-tenance experience and knowledge that existsbetween category A and B1 license holders.Conversion from category B2 to B1 or from

B1 to B2 requires 1 year of practical experi-ence practicing in the new license area. Plussuccessful completion of the partial JAR 66examinations, as specified by the CAA and/orJAR 147 approved training organization.

1.3.3 Category C certifyingengineers

The three primary categoryC qualification path-ways are relatively simple to understand and areset out in Figure 1.10.Qualification is either achieved through prac-

tising as a category B1 or B2 certifying tech-nician, for a minimum period of 3 years orentering the profession as an engineering gradu-ate from a recognized degree. Those individualswishing to gain a category C AML, using thecategory B route, will already have met theexamination criteria in full. However, thoseentering the profession as engineering graduateswill have to take category B1 or B2 knowledgeexaminations in full or in part, depending onthe nature of the degree studied. Examples of


Figure 1.8 Category B1 qualifications and experience pathways.

Figure 1.9 Category B2 qualifications and experience pathways.

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Figure 1.12 Routes to an honours degree and category A, B and C licenses.

non-standard entry methods and graduate entrymethods, together with the routes and pathwaysto professional recognition are given next.

1.3.4 Non-standard qualificationand experience pathways

Figure 1.11 illustrates in more detail two possi-ble self-starter routes. The first shows a possibleprogression route for those wishing to gain theappropriate qualifications and experience by ini-tially serving in the armed forces. The seconddetails a possible model for the 18+ schoolleaver employed in a semi-skilled role, within arelatively small aircraft maintenance company.

In the case of the semi-skilled self-starter, theexperience qualifying times would be depen-dent on individual progress, competence andmotivation. Also note that 18+ is considered tobe an appropriate age to consider entering theaircraft maintenance profession, irrespective ofthe type of license envisaged.

1.3.5 The Kingston qualificationand experience pathway

In this model, provision has been made for qual-ification and experience progression routes forcategory A, B and C AML approval and appro-priate professional recognition (Figure 1.12).

Introduction 13

Figure 1.13 Fast-track routes to category B and C AML.

Figure 1.13 also shows the various stopping-off points, for those individuals wishing topractice as either category A, B or C certifiers.Figure 1.13 shows two possible fast-track

routes for the qualification and award of eithera category B or C license. Fast track in this casemeans that because of the partnership betweenKingston University2 and KLM the total pro-gramme is recognized by the CAA for ab initioapproval, which reduces the qualifying times toa minimum, as shown in Figures 1.8–1.10. Theappropriate practical experience being deliveredat KLM’s JAR 147 approved training school atNorwich Airport.Kingston University also has a partnership

with the City of Bristol College, which is a JAR147 approved organization. With the expan-sion of Kingston’s highly successful programmethere will be more opportunities for 18+school leavers, to undertake ab initio train-ing, leading to the CAA examinations and the

award of a foundation or full B.Eng.(Hons)degree.TheRoyal Aeronautical Society (RAeS) recog-

nizes that full category B JAR 66 AML holders,with appropriate experience and responsibili-ties, meet the criteria for professional recogni-tion as incorporated engineers and may, subjectto a professional review, use the initials I.Eng.after their name.Honours degree holders, who also hold a full

category C AML may, with appropriate fur-ther learning to masters degree level, apply forrecognition as chartered engineers through theRAeS. This is the highest professional accoladefor engineers and recognized internationally asthe hallmark of engineering ability, competenceand professionalism.Figure 1.14 shows where the full category

A, B and C aircraft maintenance certifiers sit,within the professional engineering qualificationframework. Thus the category A mechanic, can


Figure 1.14 Routes to aerospace engineering professional recognition.

Table 1.1

Type of engineering degree Module exemption

Mechanical engineering bias Module 1 Mathematics and Module 2 PhysicsAeronautical engineering or Air Module 1 Mathematics, Module 2 Physics andtransport engineering bias Module 8 Basic aerodynamicsElectrical or Electronic engineering bias Module 1 Mathematics, Module 2 Physics,

Module 3 Electrical fundamentals andModule 4 Electronic fundamentals

Avionic engineering bias Module 1 Mathematics, Module 2 Physics,Module 3 Electrical fundamentals,Module 4 Electronic fundamentals andModule 8 Basic aerodynamics

Kingston University B.Eng.(Hons) aircraft Complete exemption from Modules 1 to 10.engineering degree (mechanical engineering bias) Approved as fast-track route to “C” licence

with suitable structured training and experi-ence, gain engineering technician status. Thefull category B technician, again with appro-priate structured training and experience, canapply for Incorporated Engineer recognition.The category C engineer, can with an appro-priate masters degree or bachelor (Hons) degreeand further learning to masters degree level,eventually gain professional recognition as achartered engineer.Partial exemptions from JAR 66 examina-

tions may be awarded to recognized engineering

degrees, dependent on the type of degree beingstudied. These limited exemptions, by degreetype are detailed in Table 1.1. No other exemp-tions are allowed and all other modules applica-ble to the licence category need to be passed byCAA approved JAR 66 examination.Note: The one exception, where a large

amount of exemption is given for graduates ofthe Kingston B.Eng.(Hons) aircraft engineeringdegree, which is directly aimed at preparingaircraft maintenance engineers, for their licenceexaminations.

Introduction 15

1.4 CAA licence – structure,qualifications, examinations and levels

1.4.1 Qualifications structure

The licensing of aircraft maintenance engineersis covered by international standards that arepublished by the International Civil AviationOrganisation (ICAO). In the UK, the Air Nav-igation Order (ANO) provides the legal frame-work to support these standards. The purposeof the licence is not to permit the holder to per-form maintenance but to enable the issue ofcertification for maintenance required under theANO legislation. This is whywe refer to licensedmaintenance personnel as “certifiers”.At present the CAA issue licences under two

different requirements depending on the maxi-mum take-off mass of the aircraft.For aircraft that exceeds 5700 kg, licenses are

issued under JAR 66. The JAR 66 license iscommon to all European countries who are fullmembers of the Joint Aviation Authority (JAA).The ideal being that the issue of a JAR 66 licenceby any full member country is then recognizedas having equal status in all other member coun-tries throughout Europe. There are currentlyover 20 countries throughout Europe that goto make-up the JAA. In US, the US FederalAviation Administration (USFAA) is the equiv-alent of the JAA. These two organizations havebeen harmonized to the point where for exam-ple, licences issued under JAR 66 are equiva-lent to those licences issued under FAR 66, incountries that adhere to FAA requirements.Holders of licences issued under JAR 66

requirements are considered to have achieved anappropriate level of knowledge and competence,that will enable them to undertake maintenanceactivities on commercial aircraft.Licences for light aircraft (less than 5700 kg)

and for airships, continue to be issued under theUKNational Licensing Requirements laid downin British Civil Airworthiness Requirements(BCAR) Section L. The intention is that within afew years, light aircraft will be included withinJAR 66. At present, this has implications forpeople who wish to work and obtain licencesin GA, where many light aircraft are operated.

Much of the knowledge required for the JAR 66licence, laid down in this series, is also relevantto those wishing to obtain a Section L licencefor light aircraft. Although the basic Section Llicence is narrower (see Appendix B) and is con-sidered somewhat less demanding than the JAR66 licence it is, nevertheless, highly regarded asa benchmark of achievement and competencewithin the light aircraft fraternity.As mentioned earlier, the JAR 66 license is

divided into categories A, B and C, and forcategory B license, there are two major careeroptions, either a mechanical or avionic techni-cian. For fear of bombarding you with toomuchinformation, what was not mentioned earlierwas the further subdivisions for the mechanicallicense. These sub-categories are dependent onaircraft type (fixed or rotarywing) and on enginetype (turbine or piston). For clarity, all levelsand categories of license that may be issuedby the CAA/FAA or member National AviationAuthorities (NAA) are listed below.

Levels

Category A: Line maintenance certifyingmechanic

Category B1: Line maintenance certifyingtechnician (mechanical)

Category B2: Line maintenance certifyingtechnician (avionic)

Category C: Base maintenance certifyingengineer

Note: When introduced, the light AML will becategory B3.

Sub-category AA1: Aeroplanes turbineA2: Aeroplanes pistonA3: Helicopters turbineA4: Helicopters piston

Sub-category B1B1.1: Aeroplanes turbineB1.2: Aeroplanes pistonB1.3: Helicopters turbineB1.4: Helicopters piston


Note that the experience requirements for allof the above licences are shown in Figures1.7–1.10.

Aircraft-type endorsements 3

Holders of JAR 66 aircraft maintenance licencesin category B1, B2 andCmay apply for inclusionof an aircraft-type rating subject to meeting thefollowing requirements.

1. The completion of a JAR 147 approved orJAA/NAA approved type training course onthe type of aircraft for which approval isbeing sought and one which covers the sub-jectmatter appropriate to the licence categorybeing endorsed.

2. Completion of aminimum period of practicalexperience on type, prior to application fortype rating endorsement.

Type training for category C differs from thatrequired for category B1 or B2, therefore cat-egory C type training will not qualify for typeendorsement in category B1 or B2. However,type courses at category B1 or B2 level mayallow the licence holder to qualify for categoryC level at the same time, providing they hold acategory C basic licence.Licence holders seeking type rating endorse-

ments from the CAA must hold a basic JAR 66licence granted by the UK CAA.

1.4.2 JAR 66 syllabus modules andapplicability

The JAR 66 syllabus may be taught and exam-ined on a module-by-module basis. The subjectmatter of individual modules may vary accord-ing to the category of licence being studied.The depth of the subject matter may also varyaccording to the category. Where this is thecase, in this series of books, the greatest depthof knowledge required by category will alwaysbe covered. In all, there are currently 17 mod-ules in the JAR 66 syllabus. These modules aretabulated in Table 1.2, together with Table1.3 indicating their applicably to a particularcategory and mechanical sub-category.

Table 1.2 Syllabus modules by subject

Module Content

1 Mathematics2 Physics3 Electrical fundamentals4 Electronic fundamentals5 Digital techniques and electronic

instrument systems6 Materials and hardware7 Maintenance practices8 Basic aerodynamics9 Human factors10 Aviation legislation11 Aeroplane aerodynamics, structures

and systems12 Helicopter aerodynamics, structures

and systems13 Aircraft aerodynamic structures

and systems14 Propulsion15 Gas turbine engine16 Piston engine17 Propeller18 Airship (to be developed)

1.4.3 Examinations and levels

The JAR 66 examinations are modular anddesigned to reflect the nature of the JAR 66syllabus content. These modular examinationsmay be taken on CAA premises, or on thepremises of approved JAR 147 organizations.The number and type of examination conductedby JAR 147 approved organizations will bedependent on the exact nature of their approval.A list of approved organizations and examina-tion venues will be found at the end of this bookin Appendix A. For candidates taking the fullmodular JAR 66 examinations, information onthe conduct and procedures for these examina-tions will be found in Chapter 23 of the JAAAdministrative and Guidance Material.4

The JAR66module contentmay vary in termsof the subjects covered within the module andthe level of knowledge required according towhether or not a category A, B1 or B2 licenseis being sought.Thus, in this book, we will cover in full

JAR 66 Modules 1, 2, 3, 4 and 8. Module 1(Mathematics, Chapter 2 in this book), will

Introduction 17

Table 1.3 Module applicability to category and mechanical sub-category

Module A or B1 aeroplanes with: A or B1 helicopter with: B2 avionic

Turbine engine Piston engine Turbine engine Piston engine

1 � � � � �2 � � � � �3 � � � � �4 �a �a �a �a �5 � � � � �6 � � � � �7 � � � � �8 � � � � �9 � � � � �10 � � � � �11b � � – – –12 – – � � –13c – – – – �14d – – – – �15 � – � – –16 – � – � –17 � � – – –

a This module is not applicable to category A.b Module 11 is applicable only to mechanical certifying staff.c Module 13 is only applicable to B2 avionic certifying technicians.d Module 14 offers a less in depth treatment of propulsion, designed for study by B2 avioniccertifying technicians.

be covered to the depth required by the B1and B2 technician examination. Further math-ematics (chapter 3) is also included, which isdesigned to assist understanding of Module 2,Physics. The further mathematics is not subjectto JAR 66 examination but is still consideredby the authors to be the very useful foundationknowledge. Those studying for the category Alicence should concentrate on fully understand-ing, the non-calculator mathematics given inChapter 2 of this book. They should also be ableto answer all the test questions at the end of thischapter.Module 2 (Physics, Chapter 4 in this book)

is covered to a depth suitable for category Btechnicians, no distinction is made between B1and B2 levels of understanding,5 the greatestdepth being covered for both categories, asappropriate. TheModule 2 content not requiredby category A mechanics, is mentioned in theintroduction to the chapter and reflected in thephysics test questions given at the end.

Module 3 (Electrical fundamentals, Chapter5 in this book) is covered at the category Btechnician level, with clear indications givenbetween the levels of knowledge required for thecategory A and B license requirements. Module4 (Electronic fundamentals, Chapter 6 in thisbook) is not required by category A mechan-ics but, as before, the treatment of the differinglevels of knowledge for category B1 and B2 willbe taken to the greater depth required by B2technicians. The differences in level again beingreflected in the test questions given at the end ofthe chapter.Module 8 (Basic aerodynamics, Chapter 7

in this book) will be covered in full to cate-gory B level, with no demarcation being madebetween category A and B levels. For the sakeof completeness, this chapter will also includebrief coverage of aircraft flight control takenfrom Module 11.1. The typical examinationquestions directly related to Module 8 will beclearly identified at the end of the chapter.


Full coverage of the specialist aeroplane aerody-namics, high-speed flight and rotor wing aero-dynamics, applicable to Modules 11 and 13will be covered in the third book in the series,Aircraft Aerodynamics, Structural Maintenanceand Repair.Examination papers are mainly multiple-

choice type but a written paper must also bepassed so that the licence may be issued. Can-didates may take one or more papers, at asingle examination sitting. The pass mark foreach multiple-choice paper is 75%! There isno longer any penalty marking for incorrectlyanswering individual multiple-choice questions.All multiple-choice questions set by the CAAand by approved organizations have exactly thesame form. That is, each question will contain astem (the question being asked), two distracters(incorrect answers) and one correct answer. Themultiple-choice questions given at the end ofeach chapter in this book are laid out in thisform.All multiple-choice examination papers are

timed, approximately 1min and 15 s, beingallowed for the reading and answering of eachquestion (see Table 1.4). The number of ques-tions asked depends on the module examinationbeing taken and on the category of licence beingsought. The structure of the multiple-choicepapers for each module together with the struc-ture of the written examination for issue of thelicense are given in Table 1.4.More detailed and current information on

the nature of the license examinations can befound in the appropriate CAA documentation,6

from which the examination structure detailedin Table 1.4 is extracted.

Written paperThe written paper required for licence issue con-tains four essay questions. These questions aredrawn from the JAR 66 syllabus modules asfollows:

Module Paper Question7 Maintenance practices 29 Human factors 110 Aviation legislation 1

1.5 Overview of airworthinessregulation, aircraft maintenance and itssafety culture

1.5.1 Introduction

All forms of public transport require legislationand regulation for their operation, in order toensure that safe and efficient transport oper-ations are maintained. Even with strict regu-lation, it is an unfortunate fact that incidentsand tragic accidents still occur. Indeed, thisis only to self-evident with the recent spate ofrail accidents where the Potters Bar accident in2002, may very likely be attributable to poormaintenance!When accidents occur on any public transport

system, whether travelling by sea, rail or air, itis an unfortunate fact, that loss of life or seriousinjury may involve a substantial number of peo-ple. It is also a fact that the accident rate for airtravel is extremely low and it is currently one ofthe safest forms of travel.The regulation of the aircraft industry can

only lay down the framework for the safe andefficient management of aircraft operations, inwhich aircraft maintenance plays a significantpart. It is ultimately the responsibility of theindividuals that work within the industry toensure that standards are maintained. Withrespect to aircraft maintenance, the introduc-tion of the new harmonized requirements underJAA and more recently ECAR should ensurethat high standards of aircraft maintenance andmaintenance engineering training are found notonly within the UK, but across Europe andindeed throughout many parts of the world.In order to maintain these high standards,

individuals must not only be made aware ofthe nature of the legislation and regulation sur-rounding their industry, but also they need tobe encouraged to adopt a mature, honest andresponsible attitude to all aspects of their jobrole. Where safety and personal integrity mustbe placed above all other considerations, whenundertaking aircraft maintenance activities.It is for the above reasons, that a knowl-

edge of the legislative and regulatory frameworkof the industry and the adoption of aircraft

Introduction 19

Table 1.4 Structure of JAR 66 multiple-choice examination papers

Module Number of Time allowed Module Number of Time allowedquestions (min) questions (min)

1Mathematics 10 Aviation LegislationCategory A 16 20 Category A 40 50Category B1 30 40 Category B1 40 50Category B2 30 40 Category B2 40 502 Physics 11 Aeroplane aerodynamics, structures and systemsCategory A 30 40 Category A 100 125Category B1 50 65 Category B1 130 165Category B2 50 65 Category B2 – –3 Electrical fundamentals 12 Helicopter aerodynamics, structures and systemsCategory A 20 25 Category A 90 115Category B1 50 65 Category B1 115 145Category B2 50 65 Category B2 – –4 Electronic fundamentals 13 Aircraft aerodynamics, structures and systemsCategory A – – Category A – –Category B1 20 25 Category B1 – –Category B2 40 50 Category B2 130 1655 Digital techniques/electronic instrument systems 14 PropulsionCategory A 16 20 Category A – –Category B1 40 50 Category B1 – –Category B2 70 90 Category B2 25 306Materials and hardware 15 Gas turbine engineCategory A 50 65 Category A 60 75Category B1 70 90 Category B1 90 115Category B2 60 75 Category B2 – –7Maintenance practices 16 Piston engineCategory A 70 90 Category A 50 65Category B1 80 100 Category B1 70 90Category B2 60 75 Category B2 – –8 Basic aerodynamics 17 PropellerCategory A 20 25 Category A 20 25Category B1 20 25 Category B1 30 40Category B2 20 25 Category B2 – –9 Human factorsCategory A 20 25Category B1 20 25Category B2 20 25

Note: The time given for examinations may, from time to time, be subject to change. There is currently a review pending ofexaminations time based on levels. Latest information may be obtained from the CAA website.

maintenance safety culture, becomes a vital partof the education for all individuals wishing topractice as aircraft maintenance engineers. Setout in this section is a brief introduction to theregulatory and legislative framework, togetherwithmaintenance safety culture and the vagariesof human performance. A much fuller coverageof aircraft maintenance legislation and safety

procedures will be found in, Aircraft Engineer-ing Maintenance Practices, the second book inthis series.

1.5.2 The birth of the ICAO

The international nature of current aircraftmaintenance engineering has already beenmentioned. Thus the need for conformity of


standards to ensure the continued airworthinessof aircraft that fly through international airspaceis of prime importance.As long ago asDecember 1944, a group of for-

ward thinking delegates from 52 countries cametogether in Chicago, to agree and ratify the con-vention on international civil aviation. Thus theProvisional International Civil Aviation Organ-isation (PICAO) was established. It ran in thisform until March 1947, when final ratificationfrom 26 member countries was received and itbecame the ICAO.The primary function of the ICAO,whichwas

agreed in principle at theChicago Convention in1944, was to develop international air transportin a safe and orderly manner. More formerly,the 52 member countries agreed to undersign:

certain principles and arrangements inorder that international civil aviation maybe developed in a safe and orderly mannerand that international air transport servicesmay be established on the basis of equalityof opportunity and operated soundly andeconomically.

Thus in a spirit of cooperation, designed tofoster good international relationships, betweenmember countries, the 52 member states signedup to the agreement. This was a far-sighteddecision, which has remained substantiallyunchanged up to the present. The ICAO Assem-bly is the sovereign body of the ICAO respon-sible for reviewing in detail the work of ICAO,including setting the budget and policy for thefollowing 3 years.The council, elected by the assembly for a

3-year term, is composed of 33 member states.The council is responsible for ensuring that stan-dards and recommended practices are adoptedand incorporated as annexes into the conven-tion on international civil aviation. The councilis assisted by the Air Navigation Commissionto deal with technical matters, the Air Trans-port Committee to deal with economic mattersand the Committee on Joint Support of AirNavigation Services and the FinanceCommittee.The ICAO also works closely with other

members of the United Nations (UN) and othernon-governmental organizations such as the

International Air Transport Association (IATA)and the International Federation of Air LinePilots to name but two.

1.5.3 The UK CAA

The CAA was established by an act of par-liament in 1972, as an independent specialistaviation regulator and provider of air trafficservices.7 Under the act it is responsible to thegovernment for ensuring that all aspects of avi-ation regulation are implemented and regulatedin accordance with the ANO formulated as aresult of the act.Following the separation of National Air

Traffic Services (NATS) in 2001, the CAA isnow responsible for all civil aviation functions,these are: economic regulation, airspace policy,safety regulation and consumer protection.The Economic Regulation Group (ERG) reg-

ulates airports, air traffic services and airlinesand provides advice on aviation policy from aneconomic standpoint. Its aim is to secure the bestsustainable outcome for users of air transportservices.The Directorate of Airspace Policy (DAP) is

responsible for the planning and regulation of allUK airspace including the navigation and com-munication infrastructure to support safe andefficient operations. Both civilian and militaryexperts staff this group.The Consumer Protection Group (CPG)

regulates travel organizations, manages theconsumer protection organization, air travelorganizers’ licensing (ATOL) and licenses UKairlines, in addition to other functions.The Safety Regulation Group (SRG) ensures

that UK civil aviation standards are set andachieved in a cooperative and cost-effectivemanner. SRG must satisfy itself that aircraft areproperly designed, manufactured, operated andmaintained. It is also the responsibility of thisgroup to ensure the competence of flight crews,air traffic controllers and aircraft maintenanceengineers in the form of personal licensing. Allthe major functions of this group are shown inFigure 1.15.Note: with the recent introduction of

European Aviation Safety Agency (EASA),

Introduction 21

Figure 1.15 CAA-SRG functions and responsibilities.

some of these functions (particularly with thecertification of individuals and the approval oforganizations, concerned with aircraft mainte-nance) will gradually be transferred from theCAA-SRG to EASA.

1.5.4 Civil aviation requirements

The broad international standards on airwor-thiness set up by the ICAO were backed upby detailed national standards, overseen in theUK by the National Authority for Airworthi-ness the CAA. These national standards wereknown in the UK as BCAR and in the USAas, Federal Airworthiness Regulations (FAR).Many other countries adopted one or the otherof these requirements, with their own nationalvariations.As international collaborative ventures became

more wide spread, there was increasing pressureto produce a unified set of standards, particu-larly in Europe. Thus came into being (under

the auspices of the JAA) the European JointAviation Requirements or JAR, for short. Then,with increasing collaborative ventures betweenEurope, the USA and other major economiesaround the world, there became a need toharmonize these European requirements (JAR),with those of the USA, FAR. This harmoniza-tion process is still ongoing and is not withoutdifficulties!It is unnecessary in this brief introduction to

go into detail on the exact nature of JAA in over-seeing the European JAR airworthiness require-ments and design protocols. Suffice to say8 that

the Civil Aviation Authorities of certaincountries have agreed common compre-hensive and detailed aviation requirements(JAR) with a view to minimizing type cer-tification problems on joint aviation ven-tures, to facilitate the export and import ofaviation products, and make it easier formaintenance and operations carried out in


one country to be accepted by the CAA inanother country.

One or two of the more important require-ments applicable to aircraft maintenance orga-nizations and personnel are detailed below:

JAR 25 – Requirements for large aircraft (over5700 kg)

JAR E – Requirements for aircraft enginesJAR 21 – Requirements for products and parts

for aircraftJAR 66 – Requirements for aircraft engi-

neering certifying staff, includingthe basic knowledge requirements,upon which all the books in thisseries are based

JAR 145 – Requirements for organizations oper-ating large aircraft

JAR 147 – Requirements to be met by organi-zations seeking approval to conductapproved training/examinations ofcertifying staff, as specified in JAR66.

1.5.5 Aircraft maintenanceengineering safety culture andhuman factors

If you have managed to plough your waythrough this introduction, you cannot havefailed to notice that aircraft maintenance engi-neering is a very highly regulated industry,where safety is considered paramount!Every individual working on or around air-

craft and/or their associated equipments, hasa personal responsibility for their own safetyand the safety of others. Thus, you will need tobecome familiar with your immediate work areaand recognize and avoid, the hazards associatedwith it. You will also need to be familiar withyour local emergency: first aid procedures, fireprecautions and communication procedures.Thorough coverage of workshop, aircraft

hangar and ramp safety procedures and pre-cautions will be found in Aircraft EngineeringMaintenance Practices, the second book in theseries.Coupled with this knowledge on safety,

all prospective maintenance engineers mustalso foster a responsible, honest, mature and

Figure 1.16 Control column, with base cover platefitted and throttle box assembly clearly visible.

professional attitude to all aspects of their work.You perhaps, cannot think of any circumstanceswhere you would not adopt such attitudes?However, due to the nature of aircraft main-tenance, you may find yourself working undervery stressful circumstances where your profes-sional judgement is tested to the limit!For example, consider the following scenario.As an experienced maintenance technician,

you have been taskedwith fitting the cover to thebase of the flying control column (Figure 1.16),on an aircraft that is going to leave the main-tenance hanger on engine ground runs, beforethe overnight embargo on airfield noise comesinto force, in 3 h time. It is thus important thatthe aircraft is towed to the ground running area,in time to complete the engine runs before theembargo. This will enable all outstanding main-tenance on the aircraft to be carried out overnight and so ensure that the aircraft is madeready in good time, for a scheduled flight firstthing in the morning.You start the task and when three quarters

of the way through fitment of the cover, youdrop a securing bolt, as you stand up. Youthink that you hear it travelling across the flightdeck floor. After a substantial search by torch-light, where you look not only across the floor,but also around the base of the control columnand into other possible crevices, in the immedi-ate area, you are unable to find the small bolt.Would you:

(a) Continue the search for as long as possibleand then, if the bolt was not found, complete

Introduction 23

the fit of the cover plate and look for thebolt, when the aircraft returned from groundruns?

(b) Continue the search for as long as possi-ble and then, if the bolt was not found,inform the engineer tasked with carrying outthe ground runs, to be aware that a bolt issomewhere in the vicinity of the base of thecontrol column on the flight deck floor. Thencontinue with the fit of the cover?

(c) Raise an entry in the aircraftmaintenance logfor a “loose article” on the flight deck. Thenremove the cover plate, obtain a source ofstrong light and/or a light probe kit and carryout a thorough search at base of control col-umn and around all other key controls, suchas the throttle box. If bolt is not found, allowaircraft to go on ground run and continuesearch on return?

(d) Raise an entry in the aircraft log for a “loosearticle” on the flight deck. Then immedi-ately seek advice from shift supervisor, as tocourse of action to be taken?

Had you not been an experienced technician,you would immediately inform your supervi-sor (action (d)) and seek advice as to the mostappropriate course of action. As an experiencedtechnician, what should you do? The courseof action to be taken, in this particular case,may not then be quite so obvious, it requiresjudgements to be made.Quite clearly actions (a) and (b) would be

wrong, no matter how much experience thetechnician had. No matter how long the searchcontinued, it would be essential to remove thecover plate and search the base of the con-trol column to ensure that it was not in thevicinity. Any loose article could dislodge duringflight and cause possible catastrophic jammingor fouling of the controls. If the engine run isto proceed, actions (a) and (b) are still not ade-quate. A search of the throttle box area for thebolt would also need to take place, as suggestedby action (c). Action (c) seems plausible, withthe addition of a good light source and thor-ough search of all critical areas, before the fitof the cover plate, seems a reasonable course ofaction to take, especially after the maintenance

log entry has been made, the subsequent searchfor the bolt, cannot be forgotten, so all is well?However, if you followed action (c) you

would be making important decisions, on mat-ters of safety, without consultation. No matterhow experienced you may be, you are not nec-essarily aware of the total picture, whereasyour shift supervisor, may well be! The correctcourse of action, even for the most experiencedengineer would be action (d).Suppose action (c) had been taken and on the

subsequent engine run the bolt, that had beenlodged in the throttle box, caused the throt-tle to jam in the open position. Then shuttingdown the engine, without first closing the throt-tle, could cause serious damage! It might havebeen the case that if action (d) had been fol-lowed, the shift supervisor may have been ina position to prepare another aircraft for thescheduled morning flight, thus avoiding the riskof running the engine, before the loose articlesearch had revealed the missing bolt.In any event, the aircraft would not nor-

mally be released for service until the missingbolt had been found, even if this required theuse of sophisticated radiographic equipment tofind it!The above scenario illustrates some of the pit-

falls, that even experienced aircraft maintenanceengineersmay encounter, if safety is forgotten orassumptions made. For example, because youthought you heard the bolt travel across theflight deck, you may have assumed that it couldnot possibly have landed at the base of the con-trol column, or in the throttle box. This, ofcourse, is an assumption and one of the goldenrules of safety is never assume check!When the cover was being fitted, did you have

adequate lighting for the job? Perhaps with ade-quate lighting, it might have been possible totrack the path of the bolt, as it travelled acrossthe flight deck, thus preventing its loss in the firstplace.Familiarity with emergency equipment and

procedures, as mentioned previously is an essen-tial part of the education of all aircraft main-tenance personnel. Reminders concerning theuse of emergency equipment will be found inhangars, workshops, repair bays and in many


Figure 1.17 Typical aircraft hangar first aid station.

other areas where aircraft engineering mainte-nance is practiced. Some typical examples ofemergency equipment and warning notices areshown below. Figure 1.17 shows a typical air-craft maintenance hangar first aid station, com-plete with explanatory notices, first aid box andeye irritation bottles.Figure 1.18 shows an aircraft maintenance

hangar fire point, with clearly identifiable emer-gency procedures in the event of fire and theappropriate fire appliance to use for electricalor other type of fire.Figure 1.19 shows a grinding assembly, with

associated local lighting and warning signs, foreye and ear protection. Also shown are thedrop-down shields above the grinding wheels toprevent spark burns and other possible injuriesto the hands, arms and eyes.Figure 1.20 shows a warning notice concern-

ing work being carried out on open fuel tanksand warning against the use of electrical power.In addition to this warning notice there is also

Figure 1.18 Typical aircraft hangar fire point.

a no power warning at the aircraft power point(Figure 1.21).You may feel that the module content con-

tained in this book on principles is a long wayremoved from the working environment illus-trated in these photographs. However, considerfor a moment the relatively simple task of inflat-ing a ground support trolleywheel (Figure 1.22).Still it is a common practice to measure tyre

pressures in pounds per square inch (psi), as wellas in bar (Figure 1.23). Imagine the consequen-ces of attempting to inflate such a tyre to 24 bar,instead of 24 psi, because you mis-read thegauge on the tyre inflation equipment!The need to understand units, in this partic-

ular case is most important. It cannot happenI hear you say; well unfortunately it can, theabove is an account of an actual incident. Fortu-nately the technician inflating the tyre, followedstandard safety procedures, in that he stoodbehind the tyre, rather than along side it, duringthe inflation process. The tyre separated from

Introduction 25

Figure 1.19 Grinding wheel assembly, with asso-ciated lighting and warning signs.

Figure 1.20 Open fuel tanks warning notice.

the wheel assembly and shot sideways at highvelocity. If the technician had been to the side ofthe tyre and wheel assembly he would have sus-tained serious injury! At that time this technicianwas unaware of the difference in units betweenthe bar and for him, the more familiar impe-rial units of psi. Thus the need to adopt a

Figure 1.21 Ground power warning.

Figure 1.22 Oxygen bottle trolley, showing trolleywheel.

Figure 1.23 Pressure gauges graduated in bar andin psi.

matured attitude to your foundation studiesis just as important as adopting the necessaryprofessional attitude to your on-job practicalmaintenance activities.


Completing the maintenancedocumentationWhen carrying out any form of maintenanceactivity on aircraft or aircraft equipment, itis vitally important that the appropriate doc-umentation and procedures are consulted andfollowed. This is particularly important, if themaintenance technician is unfamiliar with thework, or is new to the equipment being workedon. Even those experienced in carrying out aparticular activity should regularly consult themaintenance manual, in order to familiarizethemselves with the procedure and to estab-lish the modification state of the aircraft orequipment being worked on.The modification state of the documentation

itself should not only be checked by the schedul-ing staff, but also by the engineer assigned to thetask to ensure currency.When certifying staff sign-up for a particu-

lar maintenance activity, there signature impliesthat the job has been completed to the best oftheir ability, in accordance with the appropri-ate schedule and procedures. Any maintenanceengineer, who is subsequently found to haveproduced work that is deemed to be unsatisfac-tory, as a result of their negligence, during theexecution of such work, may be prosecuted. Itshould always be remembered by all involved inaircraft maintenance engineering that mistakescan cost lives. This is why it is so importantthat certifying staff always carry out their workto the highest professional standards, strictlyadhering to the laid-down safety standards andoperational procedures.

Human factorsThe above examples concerning the droppedbolt and the mistakes made when attemptingto inflate the ground support trolley tyre illus-trate the problems that may occur due to humanfrailty.Human factors9 impinges on everything an

engineer does in the course of their job in oneway or another, from communicating effectivelywith colleagues to ensuring they have adequatelighting to carry out their tasks. Knowledge ofthis subject has a significant impact on the safety

standards expected of the aircraft maintenanceengineer.The above quote is taken from the CAA pub-

lication (CAP 715) which provides an introduc-tion to engineering human factors for aircraftmaintenance staff, expanding on the humanfactors syllabus contain in JAR 66 Module 9.A study of human factors, as mentioned ear-

lier, is now considered to be an essential partof the aircraft maintenance engineers educa-tion. It is hoped that by educating engineers andensuring currency of knowledge and techniques,will ultimately lead to a reduction in aircraftincidents and accidents which can be attributedto human error during maintenance.The study of human factors has become so

important that for many years the CAA has co-sponsored annual international seminars ded-icated to the interchange of information andideas on the management and practice of elim-inating aviation accidents, resulting from nec-essary human intervention. Numerous learnedarticles and books have been written on humanfactors, where the motivation for its study hascome from the need to ensure high standardsof safety in high risk industries, such as nuclearpower and of course air transport!Aircraft maintenance engineers thus need to

understand, how human performance limita-tions impact on their daily work. For example,if you are the licensed aircraft engineer (LAE)responsible for a teamof technicians. It is impor-tant that you are aware of any limitations mem-bers of your team may have with respect toobvious physical constraints, like their hearingand vision. As well as more subtle limitations,such as their ability to process and interpretinformation or their fear of enclosed spaces orheights. It is not a good idea to task a technicianwith a job inside a fuel tank, if they suffer fromclaustrophobia!Social factors and other factors that may

affect human performance also need to beunderstood. Issues such as responsibility, moti-vation, peer pressure, management and supervi-sion need to be addressed. In addition to generalfitness, health, domestic and work-relatedstress, time pressures, nature of the task, rep-etition, workload and the effects of shift work.

Introduction 27

The nature of the physical environment inwhich maintenance activities are undertakenneeds to be considered. Distracting noise, fumes,illumination, climate, temperature, motion,vibration and working at height and in confinedspaces, all need to be taken into account.The importance of good two-way communi-

cation needs to be understood and practiced.Communication within and between teams,work logging and recording, keeping up-to-dateand the correct and timely dissemination ofinformation must also be understood.The impact of human factors on performance

will be emphasized, wherever and whenever it isthought appropriate, throughout all the booksin this series. There will also be a section in thesecond book in this series, on Aircraft Engineer-ing Maintenance Practices, devoted to the studyof past incidents and occurrences that can beattributed to errors in the maintenance chain.This section is called learning by mistakes.However, it is felt by the authors that human

factors as contained in JAR 66 Module 9, is sovast that one section in a textbook, will not dothe subject justice. For this reason a comprehen-sive list of references are given in Appendix C,to which the reader is referred. In particular anexcellent introduction to the subject is providedin the CAA publication: CAP 715 – An Intro-duction to Aircraft Maintenance EngineeringHuman Factors for JAR 66.We have talked so far about the nature of

human factors, but how do human factorsimpact on the integrity of aircraft maintenanceactivities? By studying previous aircraft inci-dents and accidents, it is possible to identifythe sequence of events which lead to the inci-dent and so implement procedures to try andavoid such a sequence of events, occurring inthe future.

1.5.6 The BAC One-Eleven accident

By way of an introduction to this process,we consider an accident that occurred toa BAC One-Eleven, on 10th June 1990 ataround 7.30 a.m. At this time the aircraft,which had taken off from Birmingham Airport,had climbed to a height of around 17,300 ft

Figure 1.24 A Boeing 767 left front windscreenassembly.

(5273m) over the town of Didcot in Oxford-shire, when there was a sudden loud bang. Theleft windscreen, which had been replaced priorto the flight, was blown out under the effectsof cabin pressure when it overcame the reten-tion of the securing bolts, 84 of which, out of atotal of 90, were smaller than the specified diam-eter. The commander narrowly escaped death,when he was sucked halfway out of the wind-screen aperture and was restrained by cabincrew whilst the co-pilot flew the aircraft to asafe landing at Southampton Airport.For the purposes of illustration, Figure 1.24

shows a typical front left windscreen assemblyof a Boeing 767.How could this happen? In short, a task

deemed to be safety critical was carried out byone individual, who also carried total respon-sibility for the quality of the work achieved.The installation of the windscreen was nottested after fit. Only when the aircraft was at17,300 ft, there was sufficient pressure differen-tial to check the integrity of the work! The shiftmaintenance manager, who had carried out thework, did not achieve the quality standard dur-ing the fitting process, due to inadequate care,poor trade practices, failure to adhere to com-pany standards, use of unsuitable equipmentand long-term failure by the maintenance man-ager to observe the promulgated procedures.The airlines local management, product sam-ples and quality audits had not detected theexistence of inadequate standards employed bythe shift maintenance manager because they did


not monitor directly the work practices of shiftmaintenance managers.

Engineering factorsThere is no room in this brief account of the acci-dent to detail in full all the engineering factorswhich lead up to the windscreen failure; how-ever, some of the more important factors in thechain of events are detailed below:

• Incorrect bolts had been used with the previ-ous installation (A211-7D).• Insufficient stock of the incorrect A211-7Dbolts existed in the controlled spare partscarousel dispenser. Although these bolts wereincorrect, they had proved through 4 years ofuse to be adequate.• No reference was made to the spare partscatalogue to check the required bolts’ partnumber.• The stores system, available to identify thestock level and location of the required boltswas not used.• Physical matching of the bolts was attemptedand as a consequence, incorrect bolts (A211-8C) were selected from an uncontrolled spare-parts carousel, used by the maintenancemanager.• An uncontrolled torque limiting screwdriverwas set up outside the calibration room.• A bi-hexagonal bit holder was used to winddown the bolts, resulting in the occasionalloss of the bit and the covering up of thebolt head. Hence the maintenance man-ager was unable to see that the countersunkhead of the bolts, was further recessed thannormal.• The safety platform was incorrectly posi-tioned leading to inadequate access tothe job.• The warning from the storekeeper that A211-8D bolts were required did not influence thechoice of bolts.• The amount of unfilled countersunk left bythe small bolt heads was not recognized asexcessive.• The windscreen was not designated a “vitaltask” therefore no duplicate (independent)inspection was required.

Figure 1.25 Simplified schematic cross-section ofa typical windscreen requiring external fit.

• The windscreen was not designed so thatinternal pressure would hold it in place, butwas fitted from the outside (Figure 1.25).• The shift maintenance manager was the onlyperson whose work on the night shift wasnot subject to the review of a maintenancemanager.• Poor labelling and segregation of parts in theuncontrolled spare-parts carousel.• The shift maintenance manager did not wearprescribed glasses when carrying out thewindscreen change.

The impact of human factorsThe above series of events does not tell thewhole story. For example, why was it thatthe shift maintenance manager was requiredto perform the windscreen change in the firstplace? A supervisory aircraft engineer and afurther LAE, normally part of the shift, werenot available that night. In order to achieve thewindscreen change during the night shift andhave the aircraft ready for a pre-booked wash

Introduction 29

Table 1.5

Part No. Shank length (in.) Diameter (in.) Thread size Comments

A211-8D 0.8 0.1865–0.1895 10UNF Correct boltsA211-8C 0.8 0.1605–0.1639 8UNC 84 bolts usedA211-7D 0.7 0.1865–0.1895 10UNF Bolts removed

early in themorning, the shift maintenanceman-ager decided to carry out the windscreen changeby himself. His supervisory aircraft engineerand other airframe engineer were busy rectifyinga fault on another BAC One-Eleven aircraft,which needed to be completed before departureof the aircraft the following morning.Also in the early hours of the morning when

the windscreen change took place, the bodies’circadian rhythms are at a low ebb. This, cou-pled with a high workload, may have lead totiredness and a reduced ability to concentrate.The highway staging platformwas incorrectly

positioned for easy access to the job, had thisbeen correctly positioned the maintenance man-ager may have been better able to notice thatthe bolt heads were recessed in the countersink,significantly more than usual.The assumption that the bolts removed from

the aircraft windscreen were correct was madeby the maintenance manager. Thus one of themost important dictums was ignored, neverassume check!The non-availability of the bolts (A211-7D)

even though incorrect, in the controlled spareparts carousel, lead the manager to search ina non-controlled carousel, where parts werepoorly labelled or incorrectly segregated. Thisin turn lead the manager to select the boltsusing visual and touch methods. This resultedin the final error, in the chain, being made.The bolts selected were of the correct length butwere crucially 0.026 of an inch, too small indiameter. The illustrated parts catalogue (IPC),which should have been consulted before replac-ing the old bolts, specifies that the attachmentbolts should be part number (A211-8D). Thespecification for these bolts, together with thoseselected from the carousel (A211-8C) are shownin Table 1.5.The windscreen change on this aircraft was

not considered a vital point. The CAA state

that the term “vital point” is not intended torefer to multiple fastened parts of the structure,but applies to a single point, usually in an air-craft control system. In September 1985 BCARsintroduced a requirement for duplicate inspec-tions of vital points, which are defined as: anypoint on an aircraft at which a single mal-assembly could lead to a catastrophe, resultingin loss of the aircraft or fatalities. Had thewindscreen been considered a vital maintenanceoperation, then a duplicate inspection wouldhave been performed and the excessive recess ofthe bolt heads may very well have been noticed.Also, there are no CAA requirements for a

cabin pressure check to be called up after thework has been carried out on the pressure hull.Such checks are written into the aircraft main-tenance manual at the discretion of the aircraftdesign team, and were not called up on the BACOne-Eleven. Had they been necessary, then thesub-standard integrity of the incorrectly fittedwindscreen would have been apparent.A full account of this accident, the events

leading up to it and the subsequent safety rec-ommendationswill be found on theAir AccidentInvestigationBoardwebsite,10 fromwhich someof the above account has been taken.

The safety recommendationsAs a result of the above accident and subse-quent inquiry, eight safety recommendationswere given. Briefly, these recommendations areas follows:

• The CAA should examine the applicabil-ity of self-certification to aircraft engineer-ing safety critical tasks following which thecomponents or systems are cleared for ser-vice without functional checks. Such a reviewshould include the interpretation of singlemal-assembly within the context of vitalpoints.


• British Airways should review their qualityassurance system and reporting methods, andencourage their engineers to provide feedbackfrom the shop floor.• British Airways should review the need tointroduce job descriptions and terms of ref-erence for engineering grades, including shiftmaintenance manager and above.• British Airways should provide the mecha-nism for an independent assessment of stan-dards and conduct an in depth audit intoworkpractices at Birmingham Airport.• The CAA should review the purpose andscope of their supervisory visits to airlineoperators.• The CAA should consider the need for peri-odic training and testing of engineers to ensurecurrency and proficiency.• The CAA should recognize the need for cor-rective glasses, if prescribed, in associationwith the undertaking of aircraft engineeringactivities.• The CAA should ensure that, prior to theissue of an air traffic controller (ATC) rating,a candidate undertakes an approved courseof training, that includes the theoretical andpractical handling of emergency situations.

The above recommendations are far reachingand provide an example of human factorsinvolvement, far removed from the direct main-tenance activity, but very much impacting onthe chain of events leading to an accident orserious incident. It is these complex interac-tions that may often lead to maintenance errorsbeing made, with subsequent catastrophic con-sequences.No matter how sophisticated the policies

and procedures may be, ultimately due to theinfluence of human factors, it is the integrity,attitude, education and professionalism of theindividual aircraft maintenance engineer, thatmatters most, in the elimination of maintenanceerrors.

1.5.7 Concluding remarks

It is hoped that this short introduction intothe aircraft maintenance industry has given you

an insight into the demanding and yet veryrewardingwork, offered to aircraftmaintenancecertifying staff. No matter at what point youwish to enter the industry, you will find routesand pathways that enable you to progress to anylevel, dependent only, on your own ambitionsand aspirations. The training and education toreach the top of any profession is often long andarduous and aircraft maintenance engineering isno exception!The subject matter that follows may seem a

long way removed from the environment por-trayed in this introduction and yet, it formsa vital part of your initial educational devel-opment. Therefore, you should approach thesubjects presented in Chapters 2 and 3 of thisbook, with the same amount of enthusiasm anddedication as you will with the practical activi-ties you find yourself engaged in, when qualifiedto practice your profession.The non-calculator mathematics, you are

about to meet, may seem deceptively simple.However, do remember that the pass rate is75%, as it is for all your JAR 66 examina-tions. This is likely to be significantly higher thanany other examination pass rate, you may haveencountered up till now. It is, therefore, veryimportant that you become familiar with all thesubject matter contained in the following chap-ters, if you are to be successful in your futureCAA examinations. There are numerous exam-ples, multiple-choice questions and other typesof questions provided to assist you in acquiringthe necessary standard.

References1. CAA-SRGEngineer Standards, papers 3–6 (May 2001).2. Kingston University, Rationale for Aerospace Pro-

grammes (May 2001).3. CAA-SRG, JAR-66 Information for New Applicants

Leaflet 2 Issue 16 (October 2001).4. JAA Administration and Guidance Material (1999).5. JAR-66 Appendix 2 Section 1 Levels (April 2002).6. CAA-SRG JAR-66 Syllabus and Examinations No. 6

(issued 16/10/01).7. CAA Corporate Information, page 1–3. (April 2002).8. JAR-66 Certifying Staff Maintenance, page F1 (April

2002).9. CAP715 An Introduction to Aircraft Maintenance

Human Factors for JAR-66 (January 2002).10. UKAir accident investigation branch (AAIB).www.dft.

gov.uk/stellent/groups/dft_accidentinvest_page.hcsp

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