BA038 (B777) Thread

[Chris Scott]

pacplyer,

I'm going to be a bit kinder to your post than CJ has been, particularly as you have promised not to bite. DozyWannabe has nicely summarised the main points of the A320 accident you have cited, but I hope he and the moderators will forgive me for commenting on your argument in greater detail, as your post demands.

You shouldn't believe everything you read in Wikipedia, and your quoted phrase from an AW&ST interview with the crew about 7 years after the accident is fairly meaningless, taken out of context.

Although I was flying A320s for another airline at the time (Summer 1988) of the Air France accident to which you refer – it was actually at a small airstrip at Habsheim, near Basel/Mulhouse – I was not aware of the OEBs referred to. I do not recall any prior or subsequent warning of "engine acceleration deficiency at low altitude". [I presume "altitude" means "height".] The other quoted OEB refers to barometric altitude, which is irrelevant to A/Thr or FADEC operation.

The captain evidently decided to manoeuvre the aircraft deliberately into a part of the flight envelope from which he believed it would extract itself automatically, using its unique (at the time) combination of FBW and A/Thr flight-envelope protections. The crew were apparently unaware, despite clear references in the FCOM, that the A/Thr protective mode they relied on, known as Alpha-Floor (previously well-proven on the A310 and A300-600), is inhibited below 100ftRadio, to avoid undesired operation during landing. Wikipedia quotes the captain as asserting that the "altimeter read 100ft", despite video evidence that the plane was as low as 30ft. It does not say which altimeter. We were certainly not experiencing any problems with our RadAlts over paved or unpaved surfaces. If it was the barometric altimeter, then it was the wrong one to be using (as I don't have to remind you), even if it was set to a correct QFE.

The crew would have clearly seen, despite the increasing pitch angle, that they were flying roughly level with the approaching tree tops, so they could hardly have thought they were above 100ft. Because the approach had been rushed, the thrust was still at idle, judging from the sound track of the video.

At some stage, as the trees loomed nearer, it was realised that Alpha-Floor was not providing the sudden command of TOGA thrust that they had relied on, so they "fire-walled" the throttles. The main question is: did the FADEC unnecessarily limit the engines' acceleration from whichever idle mode they were in (gear and flaps extended).

Because of the abysmal way the investigation was handled, we may never know for sure. But from the sound track, the acceleration sounds normal enough. The aeroplane was at or close to Alpha Max (just below the stall). I'm sure you are well familiar with the swing we used to get on take-off on airplanes like the 707 if we failed to "stand up" the thrust levers to let the engines stabilise at 1.2EPR (JT3D) before selecting take-off thrust (does it also happen on 747 Classics?). Now apply that swing to an incipient stall situation.

The programmed acceleration provided by the FADECs may have prevented a yaw-induced wing drop near the stall. [The FBW prevented a stall into the tree tops, ensuring the nose did not drop much, and the wings remained level.]

[If you want more information on Alpha-Floor logic and the Habsheim accident, you could start by looking at this link]:
http://www.pprune.org/forums/tech-lo...ml#post3973073


Although a spontaneous FADEC malfunction could have been responsible for the failure of an engine to accelerate in the BA038 accident, whatever unprecedented series of coding that produced the error is unlikely to have been replicated 0 – 8 seconds later in the other engine's FADEC, as phil gollin and many others have previously commented in relation to various failure mechanisms.