Kev writes:

The Airbus software has modes where its flight control computer laws
are quite different. Some of those computer laws are divided into
Ground, Flight and Landing (Flare) phases.

One claim is that he was trying to demonstrate that the airplane was
unstallable. He had reportedly done this demonstration several times
before at a slightly higher altitude, and it had always worked. Why?
Because the Airbus has what's known as Alpha Protection (pitch related)
and Alpha Floor (thrust related). Too little thrust, at too high an
angle of attack (AOA), and its computers automatically kick in and
override the pilot.

The reason the automatic protection didn't work this time was because
he went below 100', so the computers switched to Landing Mode. That
doesn't mean they do an autoland. It means they think the pilot is
landing the plane and their rules change. The Alpha Floor is disabled
so that a landing is possible at all. By the time the pilot advanced
the throttles himself, it was too late.

In addition, another Landing Mode kicks in when the Bus passes below
50' going down to 30', as he did. The computer starts changing the
stick reference for landing, so that if you have the stick pulled
back', that position soon becomes the neutral spot. This is supposed
to force the pilot to pull back more for flaring.

These are all examples of poor design. It's extremely dangerous to
put such features into FBW software unless you can be certain that all
pilots will know as much about the software as the designers did, so
that they'll know all the modes and all the combinations and
permutations of possibilities.

If you aren't going to let the pilot control the plane, why have a
pilot at all? And if the computers are going to second-guess the
pilot's intentions every step of the way without the pilot knowing it,
having a pilot is worse than not having one.

This is a good example of poor human-machine interactions, created by
poor and inadequate design.

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