Design specifications initiated by Airbus required all subcontractors to complete a Failure Mode Effects Criticality Analysis (FMECA) on every supplied component, sub system and system. The FMECA was to be constructed in such a way that the failure mode and it’s effect was to be shown down to the smallest piece part of an equipment.
Marconi who built the Flap Slat Computer (FSC) refused to comply stating that it was too time consuming and too costly. What they did was to add up the failure rates for each type of component in the FSC and then total up all of the different sums. This gave a predicted failure rate for the components but it did not account for the effects of those failures on the computer and its’ function in the Flap Slat System.
To top that off Marconi refused to supply Lucas (the constructor of the Flap drive system) with a full up FSC. What they did was to provide one control lane of the full up computer which allowed Lucas to operate their “iron bird” extending and retracting the Flaps but the single lane not having redundancy and the ability to isolate failures meant that the flaps were inadequately tested. However even without adequate testing, the Flap system was certified.
On the first revenue flight by Lufthansa to Cairo the flaps could not be retracted after landing. The aircraft had to return to Frankfurt in a non-revenue status with the flaps almost fully extended. The computer could not detect nor could it isolate the fault.
Although the German contractor that designed the Slat drive system had a full up computer their FSC was unable to detect a run-away when hydraulic pressure was applied to their “iron bird”.
I can only assume that this non-compliance by Marconi on the FSC was carried over to the Flight Control Computer.
Adding to the above the Flaps and Slats were not grounded to the wing structure.
All of the above was provided to the FAA, DGCA, CAA and the LBA and nothing was done to either chastise Marconi or recertify the Flap system.
