As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CONTROL TOWER REPORTED SMOKE COMING OUT OF AFT TAIL SECTION. AIRCRAFT RETURNED TO THE GATE. STARTED APU AND NO DEFECTS NOTED, DEFERRED APU. AT BWI, ADJUSTED APU LOAD STAT. REMOVED AND REPLACED BURNER CAN. RAN APU FOR A WHILE AND HEAVY OIL SMELL AND SMOKE DETECTED WHEN APU HAS LOAD ON IT. REMOVED AND REPLACED APU PER MM. OPS CHECKS GOOD.