HUMAN FACTOR

COMPLEX SYSTEMS / TASKS

Many modern aircraft systems are such that any one system may involve more than one trade/license category. Any one system / component may be related hydraulically, electrically, electronically or mechanically to many other systems / sub-systems.

On modern aircraft the computer system (computer, data buses and related interface units) connect almost all the aircraft systems together, one way or other. A good example is the Air Data Computer.

The Digital Air Data Computer (DADC) takes (mainly) Pitot and static pressures and converts them to digital signals where they are then put on the data bus for other computers to use.

Air data can be used in so many systems, but 2 are taken as an example, the pressurization computer (controlling cabin pressurization), will use some of this data as will the FADEC (Full Authority Digital Engine Control computer) to help run the engines.

So, several trades are involved: four license categories under BCARs sect L (Electrical, Instrument, Aeroplane’s and Engines) and 2 under JAR66 (mechanical and avionics).

It is important when tasks are performed on aircraft, that all engineers know the exact extent of their responsibilities applicable to their license/approval. It is also important that the engineer has some knowledge of all systems beyond his/her immediate certification responsibilities. This will mean that he/she will have a better understading of any consequences occurring to “other systems”,of actions taken with “immediate responsibility systems”.

When all separate trade area work is completed and serviceable it is important that nothing is left out (particularly at trade boundary interfaces). The aircraft as a whole should be serviceable.

To this and the following points should be studied.

·         Duties & responsibilities of each engineer.

·         Maintenance manuals.

·         Tasks cards (job cards).

·         Recording

·         Sufficient inspections.

·         Stage inspection/duplicate inspection.

·         Supervisory checks.

·         Liaison between trades.

Duties and Responsibilities of a Licensed Engineer.

All national authorities specify these duties, and for the UK, the CAA publish them in Airworthiness Notices. Notice number 3 specifies the certification responsibilities in relation to the ANO and JAR 145.

It relates to type licenses/authorizations issued under BCARs sect L and JAR66.

It also relates to those type licensed engineers who perform work on aircraft outside their licence responsibilities.

The notice defines such terms as:

·         Maintenance

·         Overhaul

·         Repair

It specifies the various types of certification that can be signed and it states the areas of responsibilities of the following type licence/approval/authorization categories:

·         Category A     -           Aeroplanes - Maintenance

·         Category B      -           Aeroplane/Rotorcraft - Overhaul

·         Category C      -           Engines – Maintenance

·         Category D     -           Engines – Overhaul

·         Category A&C            -           Rotorcraft – Maintenance

·         Categoty X     -           Instrument – Maintenance

·         Category X     -           Electrical – Maintenance

·         Category X     -           Autopilots – Maintenance

·         Category X     -           Combined – Maintenance

·         Category R      -           Radio – Maintenance

·         JAR66 Category A     -           Line Maintenance

·         JAR66 Category B1   -           Aeroplanes/Engines – Maintenance

B1.1    -           Aeroplanes Turbine

B1.2    -           Aeroplanes Piston

B1.3    -           Helicopters Turbine

B1.3    -           Helicopters Piston

·         JAR66 Category B2   -           Avionic systems – Maintenance

·         JAR66 Category C     -           Aircraft – Base Maintenance

The Notice specifies areas of trade responsibility together with exclusions where work is NOT permitted by certain licence/authorization holders.

It will state, particularly in relation to JAR66 categories, areas normally considered outside a specific trade into which responsibilities extend.

Manuals – Hard Copy or CD Form

These include:

·         Maintenance Manuals (AMM)

·         Wiring Manuals

·         Illustrated Parts Catalogue (IPC)

·         Structure Repair Manuals (SRM) etc

The appropriate manual should always be studied before carrying out a task. Even if the task is well known, reference should be made to the manual in case you  might have forgotten something or if there has been an amendment since the last time the task was performed.

Check that is the correct manual and check amendment state and the ‘effectivity’.

Check the work/procedure stated in the manual against your training/duties and responsibilities as a licensed engineer. If they are all compatible, then you can proceed with work. If they are not then other, more qualified, personel will have to be brought in to assist/complete the task.

If you feel the manual is incorrect in any detail/procedure then double check that you have the correct manual, it is up to date and the effectivity is verified. Check that you are working/looking at the correct aircraft component location. If after this check you still feel the manual is incorrect then the manufacturer should be contacted either direct or through your company publications office. Work should not proceed until clarification has been obtained from the manufacture.

Work Cards/Job Cards

Many organizations produce work cadrs/job cards. The procedure is printed on the cards with provision made for signatures at regular intervals, stage inspection and duplicate inspections.

The information on the cards is similar to that in the manual and is specific to the task in hand and is laid out in a, usually, more readable and logical manner.

If the task is long and / or complex the job card can be written out in such a way as to break it down into stages. If the cards are kept up to date with signatures and dates etc recorded as and when each stage is completed then a continuous record is maintained.

This continuous record is important, particularly in relation to shift working or when handing over a part completed job to another engineer.

During the handover, a de-briefing should occur between the ‘outgoing man’ and the ‘incoming man’. The de-briefing should include:

·         Checking the cards are signed and up-to-date

·         A verbal explanation of the progress of the job to-date

·         An indication of any possible problems that many arise

·         A situation report

·         A progress report on the spares situation

·         Expected (by management) completion date and time

·         Possible exchange of telephone numbers for liason purposes

Stage inspections/duplicate inspections called for on the job card should be carried out and signed for when stated and completed cards retained (after job completion) as part of the aircraft records.

Electronic Aids to Fault Finding

Making maintenance information more accessible to the aircraft engineer is one way to improve the engineer’s efficiency and improve the standard of workmanship. On-board fault computers as fitted to many modern aircraft is an example of how electronics have come to the aid of the engineer.

A more recent development is the belt warn notebook computer with a head-up display worn on the head by the engineer whilst working. The Rockwell Trekker is a good example of this type of technology.

The small computer is worn on the waist belt and the screen (liquid crystal display) is fitted by a strap to the head of the engineer. Control of the computer is by voice commands which leaves both hands free to get on with the work.

Contents of the AMM can be voice commanded and the pages/pictures are “floated” as a virtual image on the 1 inch square liquid crystal monocular head-up display.

The computer is strapped to the waist of the engineer and the monocular unit (with mic) is place on the head – with a cable attaching to the waist unit.

This system allows  both hands free to get on with the work and at the same time reduces the time spent “information gathering”. The man/woman can get on with the job whilst at the same time reading about it. There is no interruption between “information gathering” and “job execution”.

Laptop Computers

These, like the PC, can be used to read manufacture’s data such as AMMs etc. Can be used at the work location for better information access.

Boeing has recently (2001) launched a new software package for the laptop. This software includes such things as Flight Manuals, Minimum Equipment List, Operations Manual etc. Called the Boeing Laptop Tool it can also be customised to include individual aircraft data such as weights etc. Presumably other manufacturers will follow suit.

On-board Fault Computers

As systems on aircraft have become more sophisticated the need has arisen to provide on-board fault finding/BIT equipment. These simplify line maintenance by providing an on-board fault recording system/and instant checks to verify component operational serviceability.

The data generated is usually in 2 forms, operational data and maintenance data.

Operational Data will give the flight crew real-time information on the systems’s status. It will allow them to act accordingly either using an alternative system or checking with technical ground staff (radio or com/sat) on possible in-flight rectification procedures.

Maintenance Data. This  is generated by each system’s built in test equipment (BITE) which is consolidated before down loading by maintenance staff to prepare the necessary  rectification, spares procurement etc.

In general there are 3 classes of failure:

1.      Failures which have an operational impact on the current flight. These may also have an impact on subsequent dispatch depending on the minimum equipment list (MEL) and are always reported to the maintenance staff. Datalinking (comsat and sometimes by radio) can send this information ahead of the aircraft to alow maintenance to prepare the necessary rectification procedures, spares location etc.

2.      Failures with no immediate flight operational consequences. Detail are only made available to the flight crew by request on a status page. Rectification of a class 2 failure will depend in existing deferred defects and the MEL.

3.      Minor failures with no operational significance for the current flight which are not even displayed for the flight crew. They are available to the maintenance staff on request but cause no dispatch restrictions.

Each system detects and stores data about it’s own failures (internal failure) and those of its neighbouring systems which are known as external failures.

In the normal reporting mode all systems report both types of failures to the on-board maintenance system which memorises and correlates them, and displays them on the screen when requested.

The interactive menu allows engineers to establish a dialogue with any system to get detailed information on failures, status etc. The normal mode also creates a post-flight report which lists all the flight deck indications and the associated maintenance messages. This provides a powerful tool in fault rectification, as well as verbal flight crew reports and aircraft logbook entries.