On 2/6/2007 6:28:30 PM, "Capt. Geoffrey Thorpe" wrote:

A quick switch to
alternate static might have been in order (She may or may not have done
that) or a cross check with GPS (which I assume she had) might have been a
good idea too (she may or may not have done that also).
How do you know WHICH instrument is lying to you? You have to ignore your
inner ear, but sound and feel?


I replied too fast. To comment on your above: I have had my pitot heat fail
during night IMC flight through wet snow in a Bonanza V35. The first
indication to me that there was a problem was that the airspeed indication
slowly but noticably fell from my cruise of 165 its to 140 and continued to
fall.

The first thing I did was check the GPS ground speed to confirm my speed was
still roughly the same as it had been throughout the flight. I then
double-checked and recycled my pitot heat switch to see if perhaps the switch
was not on (it was) or had faulted. With indicated airspeed still falling, I
then swiped the circuit breakers to see if one had popped - None did.

With those cross checks, I came to the conclusion that the pitot heat itself
must have failed and therefore ignored the ASI. This was confirmed after I
landed by the touch test.

Alternate static won't help a frozen or otherwise blocked pitot tube, BTW.

In regards to the pilot of the Caravan, her brain was already oversaturated
by the crisis of the aircraft stalling and falling. It is understandable to
me that her brain did not register that perhaps the pitot heat was not on or
had failed. I had the luxury of only having to deal with that one problem;
the Caravan pilot had a much bigger problem on her hands.

Sound and g-forces are a good secondary indication that the aircraft is in an
unusual attitude, but I am pretty confident that I would not be able to
recover my aircraft by sound and g-forces alone. In her case, again, her
aircraft was probably unrecoverable for a short period due to icing and
perhaps a misconfigured autopilot (a/p was probably flying the majority of
the leg and was allowed to take the aircraft into the stall due to icing
before the pilot noticed), so her instruments, other than her ASI, were not
lying to her. I am surmising that it wasn't until she reached warmer air,
released the a/p, and lost some of the ice that she was able to recover.




--
Peter