You know where you are with a factory-fresh aeroplane, especially if it is an established type which has gone through its teething troubles. The manufacturer and certificating authority know where all the aircraft's components came from and has approved their design and efficacy.
Although a batch of components from the approved supplier may occasionally contain an undetected fault, it remains true that the closest that an airline can get to saying that its aeroplane is a known quantity is when the manufacturer delivers it.
Aircraft maintenance engineering is even more a complex management task than the aircraft is a complex machine. When the press waxes lyrical about the latest "bogus parts" story, few who are writing about it know the difference between a "bogus" part and a genuine second-hand part, or between an original equipment manufacturer (OEM) part and an approved component which was not made by the original supplier (non-OEM).
Beyond those two categories there is a massive grey area in which maintenance engineering management skills and judgement are tested daily. This is the area of "remanufactured" parts which may or may not be approved; and of parts - usually "fixes" - manufactured in the repair shops of maintenance organisations. In some cases it is judged reasonable for a repair organisation itself to make a component to replace the OEM part. After all, the major maintenance organisations, whether part of the airlines or third party companies, have the skills and tooling to create simple parts, especially when they are unstressed sheets or strips of metal.
But just as an original manufacturer has the responsibility to maintain the quality of original parts, if a repair shop manager decides to allow a part to be made on site, it is essential that its quality is high and that it is appropriate for the job. If the shop supervisor fails to check every repair before signing the job off - which is not always physically easy to do - an accident or incident may be waiting to happen. The incident may be nothing more than the part separating from the aircraft, and if it is unstressed and non-critical, it may be a long time before the airline even knows that it is missing.
Stressed components, often in engines, are clearly more of a critical issue, and US aero engine manufacturers General Electric and Pratt & Whitney have just written to the Federal Aviation Administration calling for drastic tightening of the regulations on standards for approved spare parts, since there is an increasing market in non-OEM, but legal, parts. GE and P&W maintain that, under present FAA rules, non-OEM parts do not have to be manufactured to the same high standards of the OEMs.
Recently, say the engine manufacturers, airline customers have notified them that they are being offered high pressure compressor and turbine blades from non-OEMs. This development undoubtedly needs careful monitoring by the FAA, which should heed the manufacturers' call.
Competition in this field is all very well, but the non-OEMs must prove that they are at least as good as the OEMs not only in quality, but the parts must be proven compatible with the engines too. There is no room for error.
Back in the realm of more humble parts, the titanium wear-strip component which fell onto the Paris runway from a Continental Airlines McDonnell Douglas DC-10 and slashed an Air France Concorde's tyre, leading to disaster, was not an OEM part. It was, however, approved for repairers to reproduce these parts. Nevertheless the Bureau Enquêtes-Accidents' preliminary report description of the component clearly registers restrained surprise at the standards employed in its manufacture, and the mere fact that the strip fell off says something.
It is impossible not to ponder the irony of this event, which on another day might have had no consequences at all: 113 people are dead, and a fleet of extraordinary airliners has been grounded. Even humble parts, if they do not measure up to the rigorous standards essential in aviation, can spell disaster for many people.
Source: Flight International
