Narrative:

The aircraft arrived late. As usual I got into the cockpit and performed my normal duties along with checking the status of the logbook. I saw that there was a deferred item on the airplane. The probe heat fault lights were deferred. I didn't question the validity of the deferral until the copilot actually turned on the probe heat and observed that the probe heat faulted and the fault lights were working. It became clear that this item was deferred in error and that maintenance would have to be notified in chicago. Unfortunately the aircraft had been flown for several days in this condition and it took me 2 legs to realize the error at no fault of the copilot. I found 2 reasons for this happening. First, when I look at the logbook I assume that when I see a deferred that it was properly written and I rarely questioned the validity of the item. Now, when something is deferred, I will look up the operational restrictions of an MEL, i.e., a 25000 ft altitude restr for an inoperative pack, and I will also go back to the original write-up to verify the validity of the deferral. The second reason for this happening, among some other obvious ones is the ambiguity or lack of consistency of the MEL itself. When deferring the angle of attack heaters, for example, it separates the MEL item for the deferral of the fault lights as does the probe heat but it further defines the failures to include the actual failure of the angle of attack heaters, which in the case of the probe heat, it fails to do. If the probe heat failures had been more specific in defining the failures I believe this incident could have been avoided.

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Original NASA ASRS Text

Title: FLC FLIES ACFT FOR 3 DAYS WITH PROBE HEAT NOT WORKING PROPERLY. FLC BELIEVES ACFT MEL NEEDS TO BE MORE SPECIFIC.

Narrative: THE ACFT ARRIVED LATE. AS USUAL I GOT INTO THE COCKPIT AND PERFORMED MY NORMAL DUTIES ALONG WITH CHKING THE STATUS OF THE LOGBOOK. I SAW THAT THERE WAS A DEFERRED ITEM ON THE AIRPLANE. THE PROBE HEAT FAULT LIGHTS WERE DEFERRED. I DIDN'T QUESTION THE VALIDITY OF THE DEFERRAL UNTIL THE COPLT ACTUALLY TURNED ON THE PROBE HEAT AND OBSERVED THAT THE PROBE HEAT FAULTED AND THE FAULT LIGHTS WERE WORKING. IT BECAME CLR THAT THIS ITEM WAS DEFERRED IN ERROR AND THAT MAINT WOULD HAVE TO BE NOTIFIED IN CHICAGO. UNFORTUNATELY THE ACFT HAD BEEN FLOWN FOR SEVERAL DAYS IN THIS CONDITION AND IT TOOK ME 2 LEGS TO REALIZE THE ERROR AT NO FAULT OF THE COPLT. I FOUND 2 REASONS FOR THIS HAPPENING. FIRST, WHEN I LOOK AT THE LOGBOOK I ASSUME THAT WHEN I SEE A DEFERRED THAT IT WAS PROPERLY WRITTEN AND I RARELY QUESTIONED THE VALIDITY OF THE ITEM. NOW, WHEN SOMETHING IS DEFERRED, I WILL LOOK UP THE OPERATIONAL RESTRICTIONS OF AN MEL, I.E., A 25000 FT ALT RESTR FOR AN INOP PACK, AND I WILL ALSO GO BACK TO THE ORIGINAL WRITE-UP TO VERIFY THE VALIDITY OF THE DEFERRAL. THE SECOND REASON FOR THIS HAPPENING, AMONG SOME OTHER OBVIOUS ONES IS THE AMBIGUITY OR LACK OF CONSISTENCY OF THE MEL ITSELF. WHEN DEFERRING THE ANGLE OF ATTACK HEATERS, FOR EXAMPLE, IT SEPARATES THE MEL ITEM FOR THE DEFERRAL OF THE FAULT LIGHTS AS DOES THE PROBE HEAT BUT IT FURTHER DEFINES THE FAILURES TO INCLUDE THE ACTUAL FAILURE OF THE ANGLE OF ATTACK HEATERS, WHICH IN THE CASE OF THE PROBE HEAT, IT FAILS TO DO. IF THE PROBE HEAT FAILURES HAD BEEN MORE SPECIFIC IN DEFINING THE FAILURES I BELIEVE THIS INCIDENT COULD HAVE BEEN AVOIDED.

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.