Air buss loss at Paris Airshow?

"Kev" wrote in message
oups.com...

Danny Dot wrote:
In about 1990 Airbus did low pass at the Paris airshow and lost the
plane.
I recall it had something to do with the throttle software thinking the
pilots were in landing mode and "refused" to go to high power for the
go-around.

Yes, the computers did think the pilot was landing, but the crash was
caused by his being too low and slow. (See other posts for more info
on the latter.)

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.

Regards, Kev

---------links snipped----------

That was not the first or last time that a flight crew got into trouble with
a new control system that they only partially understood; and I am sure that
there will be more to come.

Just as an example, Eastern Airlines lost one of the early Lockheed L-1011
aircraft in the Florida Everglades due to a chain of events which began with
a failed indicator lamp for the nose wheel. The new feature, in the
experience of the crew, was that the autopilot could be dissengaged by a
sharp pull of push on either yoke--and would remain dissengaged until either
pilot engaged it again. That was both a safety feature and a convenience
feature, since it did not require a crew member to continue to forcibly
override a rachetting capstan until the autopilot could be dissengaged. But
the crew did not fully understand the feature, or all of its implications,
at the time. Further, autopilots do operate the trim, but not perfectly,
and they happened to be trimmed very slightly nose down; with the result
that the aircraft gradually drifted down until the wheels contacted the
vegetation and water--and dug in. There were no outside visual referenced
at that place and time--and they still believed that they were on autopilot
at a constant altitude.

That's just one more relatively famous accident.

Peter