Narrative:

False fire warning in cruise flight with sunstrand T-62T-40c14 APU. Previous fire warnings prompted embraer and sunstrand to prohibit starting of this model APU in-flight. Bulletin in the aircraft operating manual states APU starts prohibited in-flight-yet APU may be used in flight with no time limitation if it was started on the ground. This flight was to be under an hour, and I elected to run the APU continuously from ground operations in ZZZ (departure airport) to zza (arrival airport) in order to have the APU generator and pressurization bleed air available if needed, since the bulletin prohibits in-flight starting, even in emergency sits. During cruise, we got an APU fire indication, and following the checklist, all fire indications ceased prior to any direction to blow fire extinguishing bottles. Flight continued normally without the APU. Upon landing, maintenance personnel inspected APU and found no sign of actual fire. I feel the bulletin procedure for preventing APU fire indications in-flight are inadequate, and do not address the actual cause of the problem. Callback conversation with reporter revealed the following information: the reporter stated the sunstrand APU now being delivered with the newer embraer 145 models have false fire warning problems. The reporter said an alert bulletin has been issued by embraer and sunstrand regarding the false fire warnings. The reporter stated the alert bulletin has prohibited the APU from in flight start but can be operated in flight if started on the ground. The reporter said maintenance found nothing and concluded it was a false warning. The reporter stated maintenance believed the sensing loop was in close proximity to the APU hot section. The reporter said this was his only occasion of false APU fire warning but believes others have been reported.

Google
 

Original NASA ASRS Text

Title: A EMBRAER 145 IN CRUISE HAD AN AUXILIARY POWER UNIT FIRE WARNING CLRED BY SHUTTING DOWN THE AUXILIARY POWER UNIT. CAUSED BY FALSE WARNING.

Narrative: FALSE FIRE WARNING IN CRUISE FLT WITH SUNSTRAND T-62T-40C14 APU. PREVIOUS FIRE WARNINGS PROMPTED EMBRAER AND SUNSTRAND TO PROHIBIT STARTING OF THIS MODEL APU INFLT. BULLETIN IN THE ACFT OPERATING MANUAL STATES APU STARTS PROHIBITED INFLT-YET APU MAY BE USED IN FLT WITH NO TIME LIMITATION IF IT WAS STARTED ON THE GND. THIS FLT WAS TO BE UNDER AN HR, AND I ELECTED TO RUN THE APU CONTINUOUSLY FROM GND OPS IN ZZZ (DEP ARPT) TO ZZA (ARR ARPT) IN ORDER TO HAVE THE APU GENERATOR AND PRESSURIZATION BLEED AIR AVAILABLE IF NEEDED, SINCE THE BULLETIN PROHIBITS IN-FLT STARTING, EVEN IN EMER SITS. DURING CRUISE, WE GOT AN APU FIRE INDICATION, AND FOLLOWING THE CHKLIST, ALL FIRE INDICATIONS CEASED PRIOR TO ANY DIRECTION TO BLOW FIRE EXTINGUISHING BOTTLES. FLT CONTINUED NORMALLY WITHOUT THE APU. UPON LNDG, MAINT PERSONNEL INSPECTED APU AND FOUND NO SIGN OF ACTUAL FIRE. I FEEL THE BULLETIN PROC FOR PREVENTING APU FIRE INDICATIONS INFLT ARE INADEQUATE, AND DO NOT ADDRESS THE ACTUAL CAUSE OF THE PROB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE SUNSTRAND APU NOW BEING DELIVERED WITH THE NEWER EMBRAER 145 MODELS HAVE FALSE FIRE WARNING PROBS. THE RPTR SAID AN ALERT BULLETIN HAS BEEN ISSUED BY EMBRAER AND SUNSTRAND REGARDING THE FALSE FIRE WARNINGS. THE RPTR STATED THE ALERT BULLETIN HAS PROHIBITED THE APU FROM IN FLT START BUT CAN BE OPERATED IN FLIGHT IF STARTED ON THE GND. THE RPTR SAID MAINT FOUND NOTHING AND CONCLUDED IT WAS A FALSE WARNING. THE RPTR STATED MAINT BELIEVED THE SENSING LOOP WAS IN CLOSE PROXIMITY TO THE APU HOT SECTION. THE RPTR SAID THIS WAS HIS ONLY OCCASION OF FALSE APU FIRE WARNING BUT BELIEVES OTHERS HAVE BEEN RPTED.

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.