Tuesday night at 16,000ft in 0c to -5c temp my airspeed indicator went to zero there was a trace of ice and it was snowing. the pito heat was on and I could see no ice on the wing strut where the pito is located. Decended to 14000 and the air speed came back. I know the pito heat works at least on the ground when I checked it. Any thoughts?
Kevin B