What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
(-23) Delta 1927, MD88, departed runway 09 at Boston, MA at 1641 EDT, 4/20/08 and declared an emergency due to smoke in the cabin. The aircraft returned and landed runway 04R at 1650 EDT without incident. Aircraft taxied to the gate. The smoke was determined to be coming from excess oil from an auxiliary power unit (APU) leak. The APU in question leaked at the original runup of the day prior to flight. An o-ring at the filler cap was replaced and the subsequent aircraft runup was found acceptable. While the aircraft was climbing out at 7000 feet smoke was detected in the cabin. The post flight inspection again indicated an APU leak. The source of the leak could not be isolated. The APU was subsequently replaced, duct burn-outs performed on the aircraft and returned to service. The deficient APU has been sent to overhaul for teardown and evaluation.
As the FAA filed it
(-23) DELTA 1927, MD88, DEPARTED RUNWAY 09 AT BOSTON, MA AT 1641 EDT, 4/20/08 AND DECLARED AN EMERGENCY DUE TO SMOKE IN THE CABIN. THE AIRCRAFT RETURNED AND LANDED RUNWAY 04R AT 1650 EDT WITHOUT INCIDENT. AIRCRAFT TAXIED TO THE GATE. THE SMOKE WAS DETERMINED TO BE COMING FROM EXCESS OIL FROM AN AUXILIARY POWER UNIT (APU) LEAK. THE APU IN QUESTION LEAKED AT THE ORIGINAL RUNUP OF THE DAY PRIOR TO FLIGHT. AN O-RING AT THE FILLER CAP WAS REPLACED AND THE SUBSEQUENT AIRCRAFT RUNUP WAS FOUND ACCEPTABLE. WHILE THE AIRCRAFT WAS CLIMBING OUT AT 7000 FEET SMOKE WAS DETECTED IN THE CABIN. THE POST FLIGHT INSPECTION AGAIN INDICATED AN APU LEAK. THE SOURCE OF THE LEAK COULD NOT BE ISOLATED. THE APU WAS SUBSEQUENTLY REPLACED, DUCT BURN-OUTS PERFORMED ON THE AIRCRAFT AND RETURNED TO SERVICE. THE DEFICIENT APU HAS BEEN SENT TO OVERHAUL FOR TEARDOWN AND EVALUATION.