Narrative:

Flight departed boston logan airport for portland, ma, on an IFR flight plan in VFR conditions. The right bleed air fail annunciator system was deferred per aircraft MEL, because the right bleed air fail annunciator had illuminated intermittently on the ground. The maintenance department and the captain decided there was an error in the annunciator system since the bleed air system was working properly and the annunciator only illuminated intermittently on the ground. During this flight to portland both bleed air fail annunciators illuminated during flight. The first officer was flying the aircraft and he called for identify of the red master warning lights. The captain idented the nature of the emergency and performed the emergency memory item -- to turn the bleed air valve to the instrument and environmental off position. The first officer called for the emergency checklist and the captain read and performed the 2 checklist items -- to turn the valve off and monitor the engine instruments. Since both bleed air valves were off, the aircraft began to depressurize. The captain elected to continue to the portland airport, because the flight was already 1/3 of the way to portland. The captain also decided to troubleshoot the bleed air system by turning each bleed air valve individually off to try to determine whether the dual bleed air fail annunciators were legitimate or whether the annunciator system was failing. In the process of troubleshooting the system both bleed air fail annunciator lights went out. It appeared as if the system was working properly even though both lights had illuminated momentarily. The captain chose to leave the left bleed air valve in the on position since the MEL for the right bleed air fail annunciator system stipulated that the right bleed air valve must remain in the instrument and environmental off position. By leaving the left bleed air valve in the on position the aircraft began to pressurize again making the trip more comfortable for the passenger. After arriving in portland the captain spoke with the maintenance department and they asked the crew to ferry the aircraft to the maintenance base. The mechanics found a small hole in the eva tubing which is the reason the annunciators both illuminated during flight. In retrospect, the captain underestimated the nature of the failure, because the right bleed air fail annunciator system has assumed to be inoperative. In the future, I think I will approach mechanical irregularities with more skepticism and not assume that because an annunciator system has been deferred that there isn't something more extensive going on with the system itself. We fly aircraft all the time that have deferred items for which we have little history about except what the previous crew or maintenance tells us. I also learned from this situation that the annunciator system was alerting us not to a complete failure of the bleed air system (when the eva tubing melts) but to an imminent failure of the system if we had continued to fly the aircraft with the bleed air valves on.

Google
 

Original NASA ASRS Text

Title: A COMMUTER FLC CONTINUED TO THE DEST AFTER HAVING RECEIVED 2 BLEED AIR FAIL ANNUNCIATORS INFLT. THE CAPT TROUBLESHOT THE PROB AND INCORRECTLY CONCLUDED THAT THE WARNING WAS NOT HARMFUL. 1 BLEED AIR SWITCH WAS KEPT IN THE ON POS TO MAINTAIN CABIN PRESSURIZATION.

Narrative: FLT DEPARTED BOSTON LOGAN ARPT FOR PORTLAND, MA, ON AN IFR FLT PLAN IN VFR CONDITIONS. THE R BLEED AIR FAIL ANNUNCIATOR SYS WAS DEFERRED PER ACFT MEL, BECAUSE THE R BLEED AIR FAIL ANNUNCIATOR HAD ILLUMINATED INTERMITTENTLY ON THE GND. THE MAINT DEPT AND THE CAPT DECIDED THERE WAS AN ERROR IN THE ANNUNCIATOR SYS SINCE THE BLEED AIR SYS WAS WORKING PROPERLY AND THE ANNUNCIATOR ONLY ILLUMINATED INTERMITTENTLY ON THE GND. DURING THIS FLT TO PORTLAND BOTH BLEED AIR FAIL ANNUNCIATORS ILLUMINATED DURING FLT. THE FO WAS FLYING THE ACFT AND HE CALLED FOR IDENT OF THE RED MASTER WARNING LIGHTS. THE CAPT IDENTED THE NATURE OF THE EMER AND PERFORMED THE EMER MEMORY ITEM -- TO TURN THE BLEED AIR VALVE TO THE INST AND ENVIRONMENTAL OFF POS. THE FO CALLED FOR THE EMER CHKLIST AND THE CAPT READ AND PERFORMED THE 2 CHKLIST ITEMS -- TO TURN THE VALVE OFF AND MONITOR THE ENG INSTS. SINCE BOTH BLEED AIR VALVES WERE OFF, THE ACFT BEGAN TO DEPRESSURIZE. THE CAPT ELECTED TO CONTINUE TO THE PORTLAND ARPT, BECAUSE THE FLT WAS ALREADY 1/3 OF THE WAY TO PORTLAND. THE CAPT ALSO DECIDED TO TROUBLESHOOT THE BLEED AIR SYS BY TURNING EACH BLEED AIR VALVE INDIVIDUALLY OFF TO TRY TO DETERMINE WHETHER THE DUAL BLEED AIR FAIL ANNUNCIATORS WERE LEGITIMATE OR WHETHER THE ANNUNCIATOR SYS WAS FAILING. IN THE PROCESS OF TROUBLESHOOTING THE SYS BOTH BLEED AIR FAIL ANNUNCIATOR LIGHTS WENT OUT. IT APPEARED AS IF THE SYS WAS WORKING PROPERLY EVEN THOUGH BOTH LIGHTS HAD ILLUMINATED MOMENTARILY. THE CAPT CHOSE TO LEAVE THE L BLEED AIR VALVE IN THE ON POS SINCE THE MEL FOR THE R BLEED AIR FAIL ANNUNCIATOR SYS STIPULATED THAT THE R BLEED AIR VALVE MUST REMAIN IN THE INST AND ENVIRONMENTAL OFF POS. BY LEAVING THE L BLEED AIR VALVE IN THE ON POS THE ACFT BEGAN TO PRESSURIZE AGAIN MAKING THE TRIP MORE COMFORTABLE FOR THE PAX. AFTER ARRIVING IN PORTLAND THE CAPT SPOKE WITH THE MAINT DEPT AND THEY ASKED THE CREW TO FERRY THE ACFT TO THE MAINT BASE. THE MECHS FOUND A SMALL HOLE IN THE EVA TUBING WHICH IS THE REASON THE ANNUNCIATORS BOTH ILLUMINATED DURING FLT. IN RETROSPECT, THE CAPT UNDERESTIMATED THE NATURE OF THE FAILURE, BECAUSE THE R BLEED AIR FAIL ANNUNCIATOR SYS HAS ASSUMED TO BE INOP. IN THE FUTURE, I THINK I WILL APCH MECHANICAL IRREGULARITIES WITH MORE SKEPTICISM AND NOT ASSUME THAT BECAUSE AN ANNUNCIATOR SYS HAS BEEN DEFERRED THAT THERE ISN'T SOMETHING MORE EXTENSIVE GOING ON WITH THE SYS ITSELF. WE FLY ACFT ALL THE TIME THAT HAVE DEFERRED ITEMS FOR WHICH WE HAVE LITTLE HISTORY ABOUT EXCEPT WHAT THE PREVIOUS CREW OR MAINT TELLS US. I ALSO LEARNED FROM THIS SIT THAT THE ANNUNCIATOR SYS WAS ALERTING US NOT TO A COMPLETE FAILURE OF THE BLEED AIR SYS (WHEN THE EVA TUBING MELTS) BUT TO AN IMMINENT FAILURE OF THE SYS IF WE HAD CONTINUED TO FLY THE ACFT WITH THE BLEED AIR VALVES ON.

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.