As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED TWO AFT SMOKE DETECTORS SOUNDING INTERMITTENTLY. *S/D* MAINTENANCE DETERMINED THAT THE CAUSE OF SMOKE IN CABIN WAS A RESULT OF PNEUMATIC SYSTEM OIL CONTAMINATION FROM THE APU. THE SUSPECT APU WAS REPLACED IN ORD ON 12/3/98. PACK BURNOUT WAS ACCOMPLISHED TO EXPEL RESIDUAL OIL IN PNEUMATIC SYSTEM. APU HAS BEEN RETURNED TO SHOP FOR ANALYSIS.