Turbine D -
An excellent post, thanks. However I do have to take issue with one aspect:
Originally Posted by
Turbine D
On the other hand, the A320 Habsheim crash was the result of the pilot going below a 50 ft threshold in which the computers assumed the pilot was trying to land. The plane did exactly what it was suppose to do according to the computers and landed in the treetops.
This is incorrect. Landing mode was never triggered. (The theory that put this forward was in fact advanced by Asseline's lawyers and repeated in the international press).
What happened was that thanks to poor briefing materials provided by AF (they were B&W photocopies, so some shades of grey were either too faint to spot easily and some disappeared altogether - and the briefing notes pointed them at the asphalt runway, not the grass one being used), the crew almost missed the Habsheim airport. To stay on schedule, rather than turn around and make another approach, Capt. Asseline elected to attempt a short final that cut it too fine and maneouvre into position during the descent.
In order to do this he did not simply disarm autothrust, he actually disabled it - by holding down the disarm buttons. This makes A/THR unavailable until reset by ground crew (it was in fact intended to be used if A/THR developed a malfunction), and therefore also inhibits alpha floor protection (which is distinct from alpha protection). In order to expedite descent he chopped the thrust back past the point required for the flypast and the engines spooled down, which is a big no-no on approach as I understand it. The descent was expedited a little too much and they went below 100ft RA shortly after crossing the threshold. Landing mode was not triggered - possibly because the RA never held a stable value long enough to do so.
The photocopied aerodrome map did not show the trees at the end of the grass runway because on the original they were a light grey shade below the threshold of the photocopier - they were spotted as a danger about halfway down the runway and the thrust levers were pushed to the TOGA position shortly afterwards. Unfortunately with the engines spooled down and alpha floor disabled with the autothrust as a result of the expedited descent, they took too long to spool back up, and the only remaining protection was alpha protection, which limits pitch attitude to preserve AoA above stall.
This, not landing mode, was the reason the aircraft did not climb when Asseline pulled up - he simply did not have the required thrust or airspeed to do so by the time the aircraft was over the trees.
In this case, had Asseline been able to override the computer completely, the aircraft would have stalled short of the trees, crashed out of control and many more would likely have died* as a result. As such, there's a degree of tragic irony that, had the A320 done as Asseline asked, he may not have survived to publicly rubbish the A320 for not doing as he asked.
[* - EDIT : The three deaths that did occur (tragically including two children) were as a result of smoke inhalation, not impact forces - and the injuries were relatively minor, with a few serious cases involving broken bones. ]