As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU-AUTO SHUTDOWN IN FLIGHT. AFTER TAKEOFF THE APU AUTO SHUTDOWN AND NR 1 ENGINE WAS ALREADY ON MEL. AIR RETURN TO GRB. MAINTENANCE DEFERRED APU DUE TO AUTO SHUTDOWN IAW MEL 49-00-1 (C) C/B PULLED PLACARDED, ENTERED INTO DRM MOX NOTIFIED. MAINTENANCE REMOVED AND REPLACED APU P/N 4501690A S/N ON SP-E977535 S/N OFF SP-E977531 IAW MAL T/C APU CHANGE LEAK AND OPS CHECK GOOD REMOVED FROM DMR MXC NOTIFIED 1376.