Re: Analysis of Air France 447 crash

In article <Xns9FB575961BAEwascana212com@xxxxxxxxxxxx>,
James Robinson <wascana@xxxxxxx> wrote:
Richard <the.sargon@xxxxxxxxx> wrote:

GPS and airspeed can be over 100 mph different, ...

Good point.

Other experienced pilots say that they take note of the aircraft
attitude and power setting as they enter bad weather, and if everything
goes to pot, just use those settings to stay on the straight and level
until they sort things out or they clear by themselves.

Hmmm, never really thought of doing that. I think that's an
excellent thing to do.

Of course, bear in mind that once ice starts degrading the
airfoil, the settings that used to keep you straight and
level won't work any more.

So the question is: Why in hell did the PF initiate an abrupt climb when
the airspeed was lost? Once he did that, they were in a real mess, and
all the other issues of pilot interface and figuring out what was going
on became more of a problem than they would have been otherwise.

One pilot instinct is to climb out of ice. (You can descend out of
it too, but in general, up is better than down when you're in the
air and can't see the ground.) Combined with not even knowing
what the airspeed was, you can wind up in a much stronger climb
than you intended.

There was an interesting case of an empty DC-9 crashing that way --
the pitot and static ports had iced up and the crew thought they
really were flying at good speed and climbing really well, when
they were on the verge of stalling out. They thought the
too-good-to-be-true numbers on the airspeed and VSI were caused
by flying light.


It looks like they didn't know what instrumentation to trust, and
struggled with trying to understand what was going on so they could take
action.

There's some truth to that. In training, they always simulated an
instrument failure by sticking a rubber suction cup over the instrument so
you couldn't use it any more. But real instruments don't fail that way.
What really happens is that the instrument looks normal to you, but it's
actually lying. Now you have conflicting readings, and you need to make
a judgement on which one to trust. And that's assuming you've realized
that the instruments are in conflict in the first place.

It still comes back to why the PF initiated the rapid climb to start
with. It would have been a non-event had he never done that.

It's scary that the left-seat pilot apparently didn't even notice that
the right-seater had the stick all the way back.

--
-Ed Falk, falk@xxxxxxxxxxxxxxxx
http://thespamdiaries.blogspot.com/
.

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