As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
BLOCK TURN BACK, FLIGHT CREW REPORTED APU AUTO SHUTDOWN, EMERGENCY SHUTDOWN DUE TO BURNING SMELL. MAINTENANCE PERFORMED AN INSPECTION AND OPERATIONAL CHECKS OF THE APU PER AMM 49-00-81-810-803. NO INDICATION OF BURNING SMELL WAS FOUND. RII INSPECTION PER GMM 85.07. RAN APU AND PACKS IAW 12-33-21-618-001. NO BURNING SMELL DETECTED.