Narrative:

Airline's maintenance control dispatched our flight with captain's compass inoperative in accordance with their MEL which proved to be out of date. The applicable MEL requires both compass systems to be operative. Maintenance control's MEL showed 2 compass systems installed with only one required for dispatch. MEL in the airplane showed 3 compass systems installed with 2 required. Airplane actually has 2 electric compass systems and one standby compass. We assumed the third compass was the standby and we were therefore legal to depart. Four days later we learned the standby was not acceptable and that the 2 mels (maintenance control's and the one in the airplane) conflicted with each other. Solution: keep manual's up to date.

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Original NASA ASRS Text

Title: MLG FLEW WITH REQUIRED COMPASS INOPERATIVE.

Narrative: AIRLINE'S MAINT CONTROL DISPATCHED OUR FLT WITH CAPT'S COMPASS INOP IN ACCORDANCE WITH THEIR MEL WHICH PROVED TO BE OUT OF DATE. THE APPLICABLE MEL REQUIRES BOTH COMPASS SYSTEMS TO BE OPERATIVE. MAINT CONTROL'S MEL SHOWED 2 COMPASS SYSTEMS INSTALLED WITH ONLY ONE REQUIRED FOR DISPATCH. MEL IN THE AIRPLANE SHOWED 3 COMPASS SYSTEMS INSTALLED WITH 2 REQUIRED. AIRPLANE ACTUALLY HAS 2 ELECTRIC COMPASS SYSTEMS AND ONE STANDBY COMPASS. WE ASSUMED THE THIRD COMPASS WAS THE STANDBY AND WE WERE THEREFORE LEGAL TO DEPART. FOUR DAYS LATER WE LEARNED THE STANDBY WAS NOT ACCEPTABLE AND THAT THE 2 MELS (MAINT CONTROL'S AND THE ONE IN THE AIRPLANE) CONFLICTED WITH EACH OTHER. SOLUTION: KEEP MANUAL'S UP TO DATE.

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.