There might be a clue in AC43.13. Here's a caution note from the pitot static testing section ( Paragraphs 12-58 and 59)

"Do not blow air through the line toward the instrument panel. This may seriously damage the instruments. Be sure to disconnect the instrument lines so no pressure can reach the instruments."

"CAUTION: To avoid rupturing the diaphragm of the airspeed indicator, apply pressure slowly and do not build up excessive pressure in the line. Release pressure slowly to avoid damaging the airspeed indicator."


Sounds like over pressure or rate of pressure change has ruptured diaphragms before. For the electronic sensor I can't see how rate would do it which leaves over pressure. Probably more than the lungs or pitot ram air alone can make.

Any chance of compressed air, fast moving water, or ice in the pitot path?
Maybe somebody 'tested' or hosed off the glider between flights.
How long has it been since the last flight when it was working.

Does the tow rope hook up where it can affect the pitot port?

Was there any moisture (or bug parts ;-) in the pitot system when you looked at it?

Interesting detective project.