Narrative:

Observed higher than normal outlet oil temperature on right CSD. When it reached yellow arc, started APU, pwred right AC bus with APU generator, turned off right main generator. Less than 1 min later, APU generator failed, AC xtie locked out. Then observed right CSD outlet temperature at red line. Disconnected right CSD, declared emergency due to possibility of fire from electrical short. Returned to stl, landed overweight at approximately 140000 pounds without incident. Maintenance drained oil from right CSD (oversvced) and reconnected CSD, placarded APU generator inoperative, released aircraft for flight. Upon inquiry by crew regarding suspected problem with APU generators, maintenance said it was 'probably a sheared drive shaft.' then why the AC xtie lockout? 'Don't know, but we'll look into it and let you know.' new information: in late september, the mechanic who worked on the aircraft delivered to me a section of the APU generator feeder cable which had been removed from the subject aircraft in the tail area beneath the aft lavatory. This cable was severely chafed with only a few strands intact, and evidence of severe arcing on both sides of the chafed area. (The cable had been completely melted on both sides.) furthermore, a protective plastic shroud required by an outstanding airworthiness directive on this model aircraft was not in place to protect the cable. The aircraft had been recently acquired from another carrier. Company is looking into maintenance history on the aircraft. Conclusions: 1) the AC xtie lockout did what it was supposed to do. 2) there was, in fact, a short and a serious risk of undetectable fire in the tail area prior to landing. 3) validation of airworthiness directive compliance may not be adequate as aircraft change owners. 4) CSD oversvcing is a continuing problem.

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Original NASA ASRS Text

Title: APU GENERATOR FEEDER CABLE SEVERELY CHAFED WITH EVIDENCE OF ARCING WAS REMOVED FROM ACFT AFTER INFLT APU CSD OVERHEAT AND SHUTDOWN.

Narrative: OBSERVED HIGHER THAN NORMAL OUTLET OIL TEMP ON R CSD. WHEN IT REACHED YELLOW ARC, STARTED APU, PWRED R AC BUS WITH APU GENERATOR, TURNED OFF R MAIN GENERATOR. LESS THAN 1 MIN LATER, APU GENERATOR FAILED, AC XTIE LOCKED OUT. THEN OBSERVED R CSD OUTLET TEMP AT RED LINE. DISCONNECTED R CSD, DECLARED EMER DUE TO POSSIBILITY OF FIRE FROM ELECTRICAL SHORT. RETURNED TO STL, LANDED OVERWT AT APPROX 140000 LBS WITHOUT INCIDENT. MAINT DRAINED OIL FROM R CSD (OVERSVCED) AND RECONNECTED CSD, PLACARDED APU GENERATOR INOP, RELEASED ACFT FOR FLT. UPON INQUIRY BY CREW REGARDING SUSPECTED PROB WITH APU GENERATORS, MAINT SAID IT WAS 'PROBABLY A SHEARED DRIVE SHAFT.' THEN WHY THE AC XTIE LOCKOUT? 'DON'T KNOW, BUT WE'LL LOOK INTO IT AND LET YOU KNOW.' NEW INFO: IN LATE SEPTEMBER, THE MECH WHO WORKED ON THE ACFT DELIVERED TO ME A SECTION OF THE APU GENERATOR FEEDER CABLE WHICH HAD BEEN REMOVED FROM THE SUBJECT ACFT IN THE TAIL AREA BENEATH THE AFT LAVATORY. THIS CABLE WAS SEVERELY CHAFED WITH ONLY A FEW STRANDS INTACT, AND EVIDENCE OF SEVERE ARCING ON BOTH SIDES OF THE CHAFED AREA. (THE CABLE HAD BEEN COMPLETELY MELTED ON BOTH SIDES.) FURTHERMORE, A PROTECTIVE PLASTIC SHROUD REQUIRED BY AN OUTSTANDING AIRWORTHINESS DIRECTIVE ON THIS MODEL ACFT WAS NOT IN PLACE TO PROTECT THE CABLE. THE ACFT HAD BEEN RECENTLY ACQUIRED FROM ANOTHER CARRIER. COMPANY IS LOOKING INTO MAINT HISTORY ON THE ACFT. CONCLUSIONS: 1) THE AC XTIE LOCKOUT DID WHAT IT WAS SUPPOSED TO DO. 2) THERE WAS, IN FACT, A SHORT AND A SERIOUS RISK OF UNDETECTABLE FIRE IN THE TAIL AREA PRIOR TO LNDG. 3) VALIDATION OF AIRWORTHINESS DIRECTIVE COMPLIANCE MAY NOT BE ADEQUATE AS ACFT CHANGE OWNERS. 4) CSD OVERSVCING IS A CONTINUING PROB.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.