As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENCODER SHOWED PROPER PRESSURE ALTITUDE FOR APPROXIMATELY 25 MINUTES. AFTER THAT TIME, ENCODER STARTED TO REPORT (PLUS) 100 FOOT ERROR EVERY 2 MINUTES UNTIL THE ERROR BECAME ABOUT 600 FEET. AFTER THAT, THE ENCODER WANDERED UP AND DOWN ABOUT 200 FEET. UNIT WAS REPLACED WITH NEW ENCODER. (X)