As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU WOULD NOT START IN THE AIR. *S/D* APU INLET DOOR ACTUATOR (R5365-1) FAILED. ACTUATOR WAS REMOVED AND REPLACED FEB 9,1999 AT IAD. OPS CHK OK. VENDOR ANALYSIS OF REMOVED UNIT INDICATED UNIT WAS COMPLETELY SEIZED. WATER WAS FOUND IN UNIT WHICH RESULTED IN UNIT SEIZURE.