As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE ENROUTE, THE PILOTS ALTIMETER (FROZE UP) AT ABOUT 8000 FT AND THE OVERSPEED HORN WENT OFF. THE PILOT RECYCLED THE ADC AND ITS OPERATION WAS RESTORED. THE ADC WAS TESTED AND NO DEFECTS WERE FOUND. THERE WAS NO EVIDENCE OF WATER OR MOISTURE IN OR AROUND THE ADC. THE ADC WAS REPLACED AND TESTED. THERE HAS BEEN NO PREVIOUS REPORTED FAILURES OF THIS SYSTEM IN THIS AIRCRAFT. (K)