Narrative:

As we leveled off at 33,000' engine #3 'B' system fire detection showed a fault. The widebody transport series at company airlines has 2 separate fire detection systems that both must detect an overheat condition in the nacelle area of each engine. If a fault is detected in one of the 2 loops it may be deactivated where only one may detect an overheat to activate the fire warning system. The 'a' loop indicated level 2 heat after the test. Over the next couple of hours the nacelle temperature indicator went from 2 to 7.9, at this time we turned off the airway 90% started drift down and shut #3 engine down. A phone patch to our maintenance in minneapolis through rainbow radio (halifax) was done and they were unable to shed any new light on our problem. It was decided between maintenance and the captain, a safe return to boston could be made on 3 engines. The captain, I remember specifically, told the first officer to declare an emergency. As the first officer picked up the microphone to advise ATC of our 90 degree left turn, descent, and emergency, a F/a walked in and asked me what was going on and if we were returning to boston. I told her we were busy and we'd get back to her later. When I got 'back in the loop' the first officer had finished his broadcast. I never heard what he said to ATC. The engine was shut down, clearance received to boston, a flight plan time, fuel burn was worked up back to boston and the return flight was uneventful. While en route the first officer questioned himself on the fact that he actually said the word 'emergency'. He had center check on it for him and then returned later and said that we had not declared an emergency. At that time we declared the emergency and continued to boston.

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Original NASA ASRS Text

Title: WDB ENROUTE PRESTWICK EXPERIENCED HIGH ENGINE TEMPERATURE. SHUT DOWN, RETURN TO BOS.

Narrative: AS WE LEVELED OFF AT 33,000' ENGINE #3 'B' SYSTEM FIRE DETECTION SHOWED A FAULT. THE WDB SERIES AT COMPANY AIRLINES HAS 2 SEPARATE FIRE DETECTION SYSTEMS THAT BOTH MUST DETECT AN OVERHEAT CONDITION IN THE NACELLE AREA OF EACH ENGINE. IF A FAULT IS DETECTED IN ONE OF THE 2 LOOPS IT MAY BE DEACTIVATED WHERE ONLY ONE MAY DETECT AN OVERHEAT TO ACTIVATE THE FIRE WARNING SYSTEM. THE 'A' LOOP INDICATED LEVEL 2 HEAT AFTER THE TEST. OVER THE NEXT COUPLE OF HRS THE NACELLE TEMP INDICATOR WENT FROM 2 TO 7.9, AT THIS TIME WE TURNED OFF THE AIRWAY 90% STARTED DRIFT DOWN AND SHUT #3 ENGINE DOWN. A PHONE PATCH TO OUR MAINT IN MINNEAPOLIS THROUGH RAINBOW RADIO (HALIFAX) WAS DONE AND THEY WERE UNABLE TO SHED ANY NEW LIGHT ON OUR PROBLEM. IT WAS DECIDED BETWEEN MAINT AND THE CAPT, A SAFE RETURN TO BOSTON COULD BE MADE ON 3 ENGINES. THE CAPT, I REMEMBER SPECIFICALLY, TOLD THE F/O TO DECLARE AN EMER. AS THE F/O PICKED UP THE MIKE TO ADVISE ATC OF OUR 90 DEG LEFT TURN, DSCNT, AND EMER, A F/A WALKED IN AND ASKED ME WHAT WAS GOING ON AND IF WE WERE RETURNING TO BOSTON. I TOLD HER WE WERE BUSY AND WE'D GET BACK TO HER LATER. WHEN I GOT 'BACK IN THE LOOP' THE F/O HAD FINISHED HIS BROADCAST. I NEVER HEARD WHAT HE SAID TO ATC. THE ENGINE WAS SHUT DOWN, CLRNC RECEIVED TO BOSTON, A FLT PLAN TIME, FUEL BURN WAS WORKED UP BACK TO BOSTON AND THE RETURN FLT WAS UNEVENTFUL. WHILE ENRTE THE F/O QUESTIONED HIMSELF ON THE FACT THAT HE ACTUALLY SAID THE WORD 'EMER'. HE HAD CENTER CHECK ON IT FOR HIM AND THEN RETURNED LATER AND SAID THAT WE HAD NOT DECLARED AN EMER. AT THAT TIME WE DECLARED THE EMER AND CONTINUED TO BOSTON.

Data retrieved from NASA's ASRS site as of August 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.