Narrative:

Prior to our departing ZZZ1 for ZZZ2, maintenance personnel swapped a faulty engine #1 fire detection unit with the APU fire detection unit. They then put APU on MEL and deactivated the APU fire detection system (circuit breakers). En route from ZZZ1 to ZZZ2, we observed a 'land as soon as possible' alert on ECAM, but no other warnings, chimes, or checklists. A system recall showed the flight warning computer thought there was an APU fire even though the APU fire detection unit was disabled. We suspected the faulty fire detection unit was the source but relayed information to maintenance center. Although they agreed it was most likely a false indication, we elected to declared an emergency and diverted to ZZZ3. On arrival, emergency vehicles confirmed there was no fire. Callback conversation with reporter revealed the following information: reporter (captain) stated that following the false engine #1 fire warning, the fire detection unit for that engine was considered to have failed, then removed and switched with the APU fire detection unit. After the diversion event, a mechanic stated that electrical jumper connection changes were required in order to make fire detections valid for an engine or for an APU position. No changes were made to either unit and so once the APU unit was installed in the engine position, unchanged, and the engine unit similarly placed in the APU position, neither one would accurately detect a fire in its installed position. The reporter has received no feedback about this event and, therefore, does not know why the false fire warning occurred. He believes that because the jumpers were not changed, the 'land as soon as possible' annunciated but the APU fire warning did not and that neither event would have occurred had the jumpers been changed. The closing comment was that he suspected this was a lack of proper maintenance event.

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Original NASA ASRS Text

Title: AN A319 RECEIVED AN ECAM 'LAND NOW' ALERT AND DIVERTED TO THE NEAREST FIELD FOR A FAULTY APU FIRE WARNING.

Narrative: PRIOR TO OUR DEPARTING ZZZ1 FOR ZZZ2, MAINT PERSONNEL SWAPPED A FAULTY ENG #1 FIRE DETECTION UNIT WITH THE APU FIRE DETECTION UNIT. THEY THEN PUT APU ON MEL AND DEACTIVATED THE APU FIRE DETECTION SYS (CIRCUIT BREAKERS). ENRTE FROM ZZZ1 TO ZZZ2, WE OBSERVED A 'LAND ASAP' ALERT ON ECAM, BUT NO OTHER WARNINGS, CHIMES, OR CHKLISTS. A SYS RECALL SHOWED THE FLT WARNING COMPUTER THOUGHT THERE WAS AN APU FIRE EVEN THOUGH THE APU FIRE DETECTION UNIT WAS DISABLED. WE SUSPECTED THE FAULTY FIRE DETECTION UNIT WAS THE SOURCE BUT RELAYED INFO TO MAINT CTR. ALTHOUGH THEY AGREED IT WAS MOST LIKELY A FALSE INDICATION, WE ELECTED TO DECLARED AN EMER AND DIVERTED TO ZZZ3. ON ARR, EMER VEHICLES CONFIRMED THERE WAS NO FIRE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR (CAPT) STATED THAT FOLLOWING THE FALSE ENG #1 FIRE WARNING, THE FIRE DETECTION UNIT FOR THAT ENG WAS CONSIDERED TO HAVE FAILED, THEN REMOVED AND SWITCHED WITH THE APU FIRE DETECTION UNIT. AFTER THE DIVERSION EVENT, A MECH STATED THAT ELECTRICAL JUMPER CONNECTION CHANGES WERE REQUIRED IN ORDER TO MAKE FIRE DETECTIONS VALID FOR AN ENG OR FOR AN APU POS. NO CHANGES WERE MADE TO EITHER UNIT AND SO ONCE THE APU UNIT WAS INSTALLED IN THE ENG POS, UNCHANGED, AND THE ENG UNIT SIMILARLY PLACED IN THE APU POS, NEITHER ONE WOULD ACCURATELY DETECT A FIRE IN ITS INSTALLED POS. THE RPTR HAS RECEIVED NO FEEDBACK ABOUT THIS EVENT AND, THEREFORE, DOES NOT KNOW WHY THE FALSE FIRE WARNING OCCURRED. HE BELIEVES THAT BECAUSE THE JUMPERS WERE NOT CHANGED, THE 'LAND ASAP' ANNUNCIATED BUT THE APU FIRE WARNING DID NOT AND THAT NEITHER EVENT WOULD HAVE OCCURRED HAD THE JUMPERS BEEN CHANGED. THE CLOSING COMMENT WAS THAT HE SUSPECTED THIS WAS A LACK OF PROPER MAINT EVENT.

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.