Narrative:

Aircraft was dispatched with the 'B' loop of the #2 engine overheat and fire detection system deferred inoperative. 'A' loop of that system was written up as working normally and tested properly on the ground. I suspected the system had been worked on overnight because departure point was an overnight maintenance base and it appeared #2 engine had been run on the ground. Everything normal until climbing through approximately 31000 ft for a cruise altitude of 33000 ft. Engine overheat light came on for #2 engine. Procedure leads you to shut down the engine if overheat light remains on. We declared an emergency and turned back to departure airport. Overheat light went out. Overheat light became intermittent. Performing fire test the system appeared normal. Engine operation appeared normal and visual check of engine appeared normal. Did not shut engine down, returned for normal landing. After reaching the gate, we performed a fire test and a fault/inoperative test for the mechanic. The fault inoperative test did not work properly because the overheat light came on during test. A few mins later the mechanic brought another mechanic to show him the indication but this time the fault/inoperative test worked properly without the overheat light coming on. The airplane was taken OTS to fix the overheat and fire detection system. Something could have possibly been done during the overnight maintenance that caused the good loop of the detector to malfunction. I will have second thoughts about taking an aircraft in the future that has one loop of the detector inoperative.

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Original NASA ASRS Text

Title: AN ACR TWIN JET PIC'S RPT ON A RETURN LAND MANDATED BY THE #2 ENG OVERHEAT WARNING COMING ON WHEN CLBING 40 MI W OF PDT, OR.

Narrative: ACFT WAS DISPATCHED WITH THE 'B' LOOP OF THE #2 ENG OVERHEAT AND FIRE DETECTION SYS DEFERRED INOP. 'A' LOOP OF THAT SYS WAS WRITTEN UP AS WORKING NORMALLY AND TESTED PROPERLY ON THE GND. I SUSPECTED THE SYS HAD BEEN WORKED ON OVERNIGHT BECAUSE DEP POINT WAS AN OVERNIGHT MAINT BASE AND IT APPEARED #2 ENG HAD BEEN RUN ON THE GND. EVERYTHING NORMAL UNTIL CLBING THROUGH APPROX 31000 FT FOR A CRUISE ALT OF 33000 FT. ENG OVERHEAT LIGHT CAME ON FOR #2 ENG. PROC LEADS YOU TO SHUT DOWN THE ENG IF OVERHEAT LIGHT REMAINS ON. WE DECLARED AN EMER AND TURNED BACK TO DEP ARPT. OVERHEAT LIGHT WENT OUT. OVERHEAT LIGHT BECAME INTERMITTENT. PERFORMING FIRE TEST THE SYS APPEARED NORMAL. ENG OP APPEARED NORMAL AND VISUAL CHK OF ENG APPEARED NORMAL. DID NOT SHUT ENG DOWN, RETURNED FOR NORMAL LNDG. AFTER REACHING THE GATE, WE PERFORMED A FIRE TEST AND A FAULT/INOP TEST FOR THE MECH. THE FAULT INOP TEST DID NOT WORK PROPERLY BECAUSE THE OVERHEAT LIGHT CAME ON DURING TEST. A FEW MINS LATER THE MECH BROUGHT ANOTHER MECH TO SHOW HIM THE INDICATION BUT THIS TIME THE FAULT/INOP TEST WORKED PROPERLY WITHOUT THE OVERHEAT LIGHT COMING ON. THE AIRPLANE WAS TAKEN OTS TO FIX THE OVERHEAT AND FIRE DETECTION SYS. SOMETHING COULD HAVE POSSIBLY BEEN DONE DURING THE OVERNIGHT MAINT THAT CAUSED THE GOOD LOOP OF THE DETECTOR TO MALFUNCTION. I WILL HAVE SECOND THOUGHTS ABOUT TAKING AN ACFT IN THE FUTURE THAT HAS ONE LOOP OF THE DETECTOR INOP.

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.