Narrative:

On originator, when APU bleed air and right pack were turned on, flight attendant said there was a loud howling noise and smoke/dust in aft galley. Shortly thereafter the left wing-body overheat light came on, the QRH checklist was completed and about 1 min after APU was shut down, the light extinguished. I notified dispatch and maintenance control of the situation. Contract maintenance was called and was advised of the situation. He talked with maintenance control and was directed to inspect the APU and determine its status. The APU was operating normally and cleared by maintenance, however, maintenance control decided to MEL the APU (MEL 49-1) to alleviate any subsequent problem. Let me say at this time that all parties had been advised of the wing-body overheat light, and the logbook write-up included wing-body overheat and smoke/dust in the cabin. While discussing the write-up and MEL, dispatch and I both were uneasy about how the wing-body overheat discrepancy had been addressed and if it had been cleared. Maintenance control assured us both that the MEL on the APU cleared the aircraft for flight. We proceeded on flight to boise, where I again talked to dispatch about the situation and he advised me the plane was to be removed from service in las vegas. Upon arrival in las vegas, it was decided by dispatch, chief pilot, pilot safety representative and myself that the correct course of action to be a complete inspection of the APU and all bleed ducting to find the cause of the problem (wing-body overheat light) prior to clearing the aircraft for further flight. This was accomplished by maintenance in las vegas and a blown bleed duct seal or clamp was discovered to be the source of the problem, hot air had blown off the wing-body overheat sensor causing the light to illuminate. This also caused the smoke/dust to enter the cabin through the aft lavatory area. This was repaired, tested normal and all system cleared for flight. Although, when we left seattle the first officer and I both believed the plane was airworthy and all proper channels and clrncs had been covered. Later discussion with dispatch, chief pilot and safety representative concluded that the initial logbook write-up including the wing-body overheat light probably had not been sufficiently cleared with MEL 49-1. It appears that previous similar incidents had gotten the attention of FAA auditors and they interpreted it differently than maintenance. I would say we all need to get on the same page and not put the pilots and dispatch in an awkward situation in the clearing of this type of discrepancy. I also could have utilized the chief pilot channel at an earlier stage of the discussions for his input.

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Original NASA ASRS Text

Title: PNEUMATIC DUCT FAILURE DURING INITIAL APU START RESULTS IN A L WING-BODY OVERHEAT LIGHT AND DUST AND SMOKE IN THE GALLEY OF A B737-300. QUESTION WAS RAISED AS TO PROPER DEFERRAL BY MAINT.

Narrative: ON ORIGINATOR, WHEN APU BLEED AIR AND R PACK WERE TURNED ON, FLT ATTENDANT SAID THERE WAS A LOUD HOWLING NOISE AND SMOKE/DUST IN AFT GALLEY. SHORTLY THEREAFTER THE L WING-BODY OVERHEAT LIGHT CAME ON, THE QRH CHKLIST WAS COMPLETED AND ABOUT 1 MIN AFTER APU WAS SHUT DOWN, THE LIGHT EXTINGUISHED. I NOTIFIED DISPATCH AND MAINT CTL OF THE SIT. CONTRACT MAINT WAS CALLED AND WAS ADVISED OF THE SIT. HE TALKED WITH MAINT CTL AND WAS DIRECTED TO INSPECT THE APU AND DETERMINE ITS STATUS. THE APU WAS OPERATING NORMALLY AND CLRED BY MAINT, HOWEVER, MAINT CTL DECIDED TO MEL THE APU (MEL 49-1) TO ALLEVIATE ANY SUBSEQUENT PROB. LET ME SAY AT THIS TIME THAT ALL PARTIES HAD BEEN ADVISED OF THE WING-BODY OVERHEAT LIGHT, AND THE LOGBOOK WRITE-UP INCLUDED WING-BODY OVERHEAT AND SMOKE/DUST IN THE CABIN. WHILE DISCUSSING THE WRITE-UP AND MEL, DISPATCH AND I BOTH WERE UNEASY ABOUT HOW THE WING-BODY OVERHEAT DISCREPANCY HAD BEEN ADDRESSED AND IF IT HAD BEEN CLRED. MAINT CTL ASSURED US BOTH THAT THE MEL ON THE APU CLRED THE ACFT FOR FLT. WE PROCEEDED ON FLT TO BOISE, WHERE I AGAIN TALKED TO DISPATCH ABOUT THE SIT AND HE ADVISED ME THE PLANE WAS TO BE REMOVED FROM SVC IN LAS VEGAS. UPON ARR IN LAS VEGAS, IT WAS DECIDED BY DISPATCH, CHIEF PLT, PLT SAFETY REPRESENTATIVE AND MYSELF THAT THE CORRECT COURSE OF ACTION TO BE A COMPLETE INSPECTION OF THE APU AND ALL BLEED DUCTING TO FIND THE CAUSE OF THE PROB (WING-BODY OVERHEAT LIGHT) PRIOR TO CLRING THE ACFT FOR FURTHER FLT. THIS WAS ACCOMPLISHED BY MAINT IN LAS VEGAS AND A BLOWN BLEED DUCT SEAL OR CLAMP WAS DISCOVERED TO BE THE SOURCE OF THE PROB, HOT AIR HAD BLOWN OFF THE WING-BODY OVERHEAT SENSOR CAUSING THE LIGHT TO ILLUMINATE. THIS ALSO CAUSED THE SMOKE/DUST TO ENTER THE CABIN THROUGH THE AFT LAVATORY AREA. THIS WAS REPAIRED, TESTED NORMAL AND ALL SYS CLRED FOR FLT. ALTHOUGH, WHEN WE LEFT SEATTLE THE FO AND I BOTH BELIEVED THE PLANE WAS AIRWORTHY AND ALL PROPER CHANNELS AND CLRNCS HAD BEEN COVERED. LATER DISCUSSION WITH DISPATCH, CHIEF PLT AND SAFETY REPRESENTATIVE CONCLUDED THAT THE INITIAL LOGBOOK WRITE-UP INCLUDING THE WING-BODY OVERHEAT LIGHT PROBABLY HAD NOT BEEN SUFFICIENTLY CLRED WITH MEL 49-1. IT APPEARS THAT PREVIOUS SIMILAR INCIDENTS HAD GOTTEN THE ATTN OF FAA AUDITORS AND THEY INTERPRETED IT DIFFERENTLY THAN MAINT. I WOULD SAY WE ALL NEED TO GET ON THE SAME PAGE AND NOT PUT THE PLTS AND DISPATCH IN AN AWKWARD SIT IN THE CLRING OF THIS TYPE OF DISCREPANCY. I ALSO COULD HAVE UTILIZED THE CHIEF PLT CHANNEL AT AN EARLIER STAGE OF THE DISCUSSIONS FOR HIS INPUT.

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.