What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
The APU had performed an auto shutdown immediately prior to the event flight and was deferred per the operators approved mel/cdl. Subsequent to the air return flight, it was determined that, immediately prior to and during the failure of the APU, an uncontained oil leak developed within and external to the APU compartment causing ingestion of turbine oil into the APU inlet and the aircraft pneumatic system resulting in smoke inside the aircraft.
Crew members submitted asap reports. Pilot erc accepted and reviewed both reports.
As the FAA filed it
THE APU HAD PERFORMED AN AUTO SHUTDOWN IMMEDIATELY PRIOR TO THE EVENT FLIGHT AND WAS DEFERRED PER THE OPERATORS APPROVED MEL/CDL. SUBSEQUENT TO THE AIR RETURN FLIGHT, IT WAS DETERMINED THAT, IMMEDIATELY PRIOR TO AND DURING THE FAILURE OF THE APU, AN UNCONTAINED OIL LEAK DEVELOPED WITHIN AND EXTERNAL TO THE APU COMPARTMENT CAUSING INGESTION OF TURBINE OIL INTO THE APU INLET AND THE AIRCRAFT PNEUMATIC SYSTEM RESULTING IN SMOKE INSIDE THE AIRCRAFT.
CREW MEMBERS SUBMITTED ASAP REPORTS. PILOT ERC ACCEPTED AND REVIEWED BOTH REPORTS.