Another Airbus loss of control incident

Posted on 15. Apr, 2010 by in Airline Safety, Blog

An A330 on Cathay Pacific (CX) Flight 780 experienced un-commanded power changes causing the crew to land at an excessive speed — nearly double the normal approach speed. The normal speed at their weight was reported to be 130 knots, the aircraft touched down at 239. The Rolls Royce Trent 700 engines are controlled by Full Authority Digital Engine Controllers (fly by wire). Throttles that do what they want despite the position selected by the operator; starting to sound familiar? Toyota maybe? Toyota announced today they are going to do an expansive test on their Lexus version of an SUV, I suspect they got a nudge. Quick action; I wonder if an extensive test will be done on fly-by-wire applications?

Unconnected to A330 problems of late? Maybe, maybe not; I think not. The FADECs are integrated into the ADIRU’s (aircraft computers) that control every aspect of flight. In the recent control excursions the pitot system has been blamed (AF, NWA, etc) and in the case of the QANTAS excursions the angle of attack system (AOA). Now we get FADEC (duel, very unlikely) failures. There is not a single point of failure; unless you dig a bit deeper and analyze where the information is processed and acted upon. The ADIRU #1. How is engine thrust related? If the ADIRU senses the aircraft approaching stall; taking input from speed (pitot) or angle of attack the engines will be directed to over-ride the pilot and run power up and if the AOA spikes the flight controls will be directed to push negative g. Ah Ha!

Remember the engines on Sully’s A320 would have still produced thrust, probably allowing him to reach an airfield. However the FADECs over-rode the crew and shut them down. Humans are smarter than computers, they understand the unquantifiable; for example it is better to burn engines up then go for a swim.

Back in the day, when we fought an F-16 slow we didn’t fight the aircraft (we’d loose) we fought the computer. It would over-ride the pilot exposing him to a guns shot. The FA-18 was different (also fly-by-wire); if you wanted to fly zero airspeed it would let you, the pilot had the over-all control. Not that I haven’t witnessed a fight for control between an ex A-7 pilot and his brand new F-18 (Hornet does a hands off catapult launch) off the cat. However, in general the Navy wanted the pilot to be the final arbiter. Personally I agree.