Narrative:

Approximately 30-40 mins after departing tucson, there was a very brief, staccato sounding of the fire warning bell and light. It was so brief that neither pilot was initially able to tell if it was for the engine or the APU. After 15- 30 seconds, the bell and light started again, still intermittent, but steadily increasing over the next 2 mins until it became a steady bell and light. The APU had been shut down shortly after takeoff, and had been off for at least 25 mins. The egt and ammeter indicators indicated that the APU had been shut down and was not operating, reading less than 100 degrees egt and 0 amps. Even with these indications, the crew elected to implement the company's immediate and reference actions: immediate action: APU fire handle, pull and rotate. Reference action: if the light in the handle remains on, land at the nearest suitable airport. Once the immediate action was accomplished, the bell and light decreased in frequency in occurrence, eventually ceasing after approximately 45 seconds. After about another 45 seconds, the bell sounded for less than a second and was silent for remainder of the flight of approximately 1 hour. As the bell and light did not remain on, the decision was made to continue to the scheduled destination, unless the light were to re-illuminate on steady, whereupon the crew agreed we would divert to the nearest suitable airport. After these actions, the captain contacted maintenance and dispatch. He informed them of what had occurred and the actions that had been accomplished. As I was flying and working with ATC, I was not privy to all the discussions, but did hear both agencies concur with our actions and decision to continue to denver. At no time while I was able to monitor the discussion, did maintenance give any other suggestions about doing any further troubleshooting. After the captain talked with these agencies, he had the 'a' flight attendant come forward and briefed her on what had happened. He had her go to the aircraft rear to see if there were any signs or indications of a problem. She reported no unusual indications. The previous evening when the crew had landed the same aircraft in tucson, we were unable to get bleed air from the APU. A write-up was made in the logbook and air carrier contacted by the captain. When the crew returned the next morning to the aircraft, the item had been cleared by having the air load control valve replaced. APU operation on the ground in tucson and during the brief period it was in operation after takeoff was normal.

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Original NASA ASRS Text

Title: FALSE WARNING, APU FIRE.

Narrative: APPROX 30-40 MINS AFTER DEPARTING TUCSON, THERE WAS A VERY BRIEF, STACCATO SOUNDING OF THE FIRE WARNING BELL AND LIGHT. IT WAS SO BRIEF THAT NEITHER PLT WAS INITIALLY ABLE TO TELL IF IT WAS FOR THE ENG OR THE APU. AFTER 15- 30 SECONDS, THE BELL AND LIGHT STARTED AGAIN, STILL INTERMITTENT, BUT STEADILY INCREASING OVER THE NEXT 2 MINS UNTIL IT BECAME A STEADY BELL AND LIGHT. THE APU HAD BEEN SHUT DOWN SHORTLY AFTER TKOF, AND HAD BEEN OFF FOR AT LEAST 25 MINS. THE EGT AND AMMETER INDICATORS INDICATED THAT THE APU HAD BEEN SHUT DOWN AND WAS NOT OPERATING, READING LESS THAN 100 DEGS EGT AND 0 AMPS. EVEN WITH THESE INDICATIONS, THE CREW ELECTED TO IMPLEMENT THE COMPANY'S IMMEDIATE AND REF ACTIONS: IMMEDIATE ACTION: APU FIRE HANDLE, PULL AND ROTATE. REF ACTION: IF THE LIGHT IN THE HANDLE REMAINS ON, LAND AT THE NEAREST SUITABLE ARPT. ONCE THE IMMEDIATE ACTION WAS ACCOMPLISHED, THE BELL AND LIGHT DECREASED IN FREQ IN OCCURRENCE, EVENTUALLY CEASING AFTER APPROX 45 SECONDS. AFTER ABOUT ANOTHER 45 SECONDS, THE BELL SOUNDED FOR LESS THAN A SECOND AND WAS SILENT FOR REMAINDER OF THE FLT OF APPROX 1 HR. AS THE BELL AND LIGHT DID NOT REMAIN ON, THE DECISION WAS MADE TO CONTINUE TO THE SCHEDULED DEST, UNLESS THE LIGHT WERE TO RE-ILLUMINATE ON STEADY, WHEREUPON THE CREW AGREED WE WOULD DIVERT TO THE NEAREST SUITABLE ARPT. AFTER THESE ACTIONS, THE CAPT CONTACTED MAINT AND DISPATCH. HE INFORMED THEM OF WHAT HAD OCCURRED AND THE ACTIONS THAT HAD BEEN ACCOMPLISHED. AS I WAS FLYING AND WORKING WITH ATC, I WAS NOT PRIVY TO ALL THE DISCUSSIONS, BUT DID HEAR BOTH AGENCIES CONCUR WITH OUR ACTIONS AND DECISION TO CONTINUE TO DENVER. AT NO TIME WHILE I WAS ABLE TO MONITOR THE DISCUSSION, DID MAINT GIVE ANY OTHER SUGGESTIONS ABOUT DOING ANY FURTHER TROUBLESHOOTING. AFTER THE CAPT TALKED WITH THESE AGENCIES, HE HAD THE 'A' FLT ATTENDANT COME FORWARD AND BRIEFED HER ON WHAT HAD HAPPENED. HE HAD HER GO TO THE ACFT REAR TO SEE IF THERE WERE ANY SIGNS OR INDICATIONS OF A PROB. SHE RPTED NO UNUSUAL INDICATIONS. THE PREVIOUS EVENING WHEN THE CREW HAD LANDED THE SAME ACFT IN TUCSON, WE WERE UNABLE TO GET BLEED AIR FROM THE APU. A WRITE-UP WAS MADE IN THE LOGBOOK AND ACR CONTACTED BY THE CAPT. WHEN THE CREW RETURNED THE NEXT MORNING TO THE ACFT, THE ITEM HAD BEEN CLRED BY HAVING THE AIR LOAD CTL VALVE REPLACED. APU OP ON THE GND IN TUCSON AND DURING THE BRIEF PERIOD IT WAS IN OP AFTER TKOF WAS NORMAL.

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.