Darkwing wrote:
"Ron Snipes" wrote in message
I think that is a thermal indicator. They beep faster as you gain
altitude
in a thermal.

That is correct. An "audio variometer" might be the term to use.
Glider pilots call it "the audio". The increase in volume and rate
indicates a quickly increasing and sustained rate of climb. He hit a
strong thermal concurrent with the upset that brought him down.

It's not uncommon, though sloppy, for gliders to stall as they pitch up
to enter and circle in a thermal. I have no familiarity with flexible
wing aircraft. I wonder if a 'sharp edged' thermal can momentarily
increase the wing's angle of attack to the stall angle since the delta
between forward speed and the thermal's vertical speed is relatively
small. A strong thermal can easily have a sustained vertical speed of
10knots, and I'm guessing a flex wing aircraft can have a minimum
forward spped of 15knots or less (?).