Narrative:

On jul/xx/97 at approximately XA45 I received word that aircraft XXXX was inbound from xyz with an APU fire detector inoperative and would arrive at approximately XB55. The item was listed as a must fix due to routing. The aircraft was scheduled for a 20 min or less turn. The item had been deferred by bbbmm out of xyz. I informed my lead that it would not be possible to fix the problem in the turn time and he should look for a plane change. This was accomplished and the aircraft was rerouted so the item could be deferred. When the aircraft arrived at ZZZ I did a quick operation of the system and found that it did work with the exceptions I noted in the text of the log write-up. I felt the problem, although unfamiliar to me, fell within the limits of the MEL. I discussed it with a line maintenance controller who felt the same way I did. That is the item could be deferred with the APU left in operation. The controller changed the MEL reference and I released the aircraft for service. The aircraft flew to YYY. On the way back at approximately XZ30 in-flight with the APU shut down the crew got an APU fire warning. They followed procedures and diverted to abc. After an inspection and finding it was a false alarm the aircraft continued in service. Being under pressure due to the time constraints, outbound crew to have the APU operable if at all possible, consideration for passenger overall comfort due to hot WX in YYY and just wanting to accommodate everyone after coming back after my days off, I opted to leave the APU in service. My 34+ yrs of experience says that if I had any questions I should have opted for completely inoperative'ing the system. The fact that I wrote the exceptions to the operations test in the text of the write-up indicates to me, in hindsight, that I did have questions. In hindsight I let my usual hard nose approach to the operation slip and outside pressures influence my judgement.

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Original NASA ASRS Text

Title: A B737-300 IN CRUISE DIVERTED DUE TO A FALSE APU FIRE WARNING WHICH HAD BEEN DEFERRED TO ALLOW GND APU OP.

Narrative: ON JUL/XX/97 AT APPROX XA45 I RECEIVED WORD THAT ACFT XXXX WAS INBOUND FROM XYZ WITH AN APU FIRE DETECTOR INOP AND WOULD ARRIVE AT APPROX XB55. THE ITEM WAS LISTED AS A MUST FIX DUE TO ROUTING. THE ACFT WAS SCHEDULED FOR A 20 MIN OR LESS TURN. THE ITEM HAD BEEN DEFERRED BY BBBMM OUT OF XYZ. I INFORMED MY LEAD THAT IT WOULD NOT BE POSSIBLE TO FIX THE PROB IN THE TURN TIME AND HE SHOULD LOOK FOR A PLANE CHANGE. THIS WAS ACCOMPLISHED AND THE ACFT WAS REROUTED SO THE ITEM COULD BE DEFERRED. WHEN THE ACFT ARRIVED AT ZZZ I DID A QUICK OP OF THE SYS AND FOUND THAT IT DID WORK WITH THE EXCEPTIONS I NOTED IN THE TEXT OF THE LOG WRITE-UP. I FELT THE PROB, ALTHOUGH UNFAMILIAR TO ME, FELL WITHIN THE LIMITS OF THE MEL. I DISCUSSED IT WITH A LINE MAINT CTLR WHO FELT THE SAME WAY I DID. THAT IS THE ITEM COULD BE DEFERRED WITH THE APU LEFT IN OPERATION. THE CTLR CHANGED THE MEL REF AND I RELEASED THE ACFT FOR SVC. THE ACFT FLEW TO YYY. ON THE WAY BACK AT APPROX XZ30 INFLT WITH THE APU SHUT DOWN THE CREW GOT AN APU FIRE WARNING. THEY FOLLOWED PROCS AND DIVERTED TO ABC. AFTER AN INSPECTION AND FINDING IT WAS A FALSE ALARM THE ACFT CONTINUED IN SVC. BEING UNDER PRESSURE DUE TO THE TIME CONSTRAINTS, OUTBOUND CREW TO HAVE THE APU OPERABLE IF AT ALL POSSIBLE, CONSIDERATION FOR PAX OVERALL COMFORT DUE TO HOT WX IN YYY AND JUST WANTING TO ACCOMMODATE EVERYONE AFTER COMING BACK AFTER MY DAYS OFF, I OPTED TO LEAVE THE APU IN SVC. MY 34+ YRS OF EXPERIENCE SAYS THAT IF I HAD ANY QUESTIONS I SHOULD HAVE OPTED FOR COMPLETELY INOP'ING THE SYS. THE FACT THAT I WROTE THE EXCEPTIONS TO THE OPS TEST IN THE TEXT OF THE WRITE-UP INDICATES TO ME, IN HINDSIGHT, THAT I DID HAVE QUESTIONS. IN HINDSIGHT I LET MY USUAL HARD NOSE APCH TO THE OP SLIP AND OUTSIDE PRESSURES INFLUENCE MY JUDGEMENT.

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.