Narrative:

Departed with MEL 36-6 issued for APU bleed valve. After we arrived in ZZZZ; we attempted to start the APU for its generator. When the APU master knob was moved to 'run' position; the 'APU fail' message was displayed on EICAS. I contacted dispatch who then started a conference call to maintenance control. I described the situation to the maintenance controller; who then issued MEL 49-1 to defer the entire APU. Maintenance control; dispatch; and I failed to notice that MEL 36-6 cannot be in effect with MEL 49-1. Dispatch informed us en route about the discrepancy. The xref between the MEL's was only marked for MEL 36-6; and no one thought to look at the earlier issued MEL. To help avoid a similar event in the future; it would be helpful to have more complete xrefing of MEL's. In addition; a more careful review of all issued MEL's would have caught the error. Supplemental information from acn 810286: dispatcher working this aircraft on next flight leg caught MEL discrepancy and brought it to my attention. I contacted maintenance controller who originally issued MEL with me. He; in turn; reviewed MEL book with his supervisor. I reviewed MEL book with my supervisor and advised crew (via ACARS) of discrepancy. My supervisor sent an email to flight department requesting MEL book correction/clarification. Maintenance control supervisor also requested correction/clarification from flight department. Supplemental information from acn 810293: crew anticipated a slight delay in obtaining ground power. They attempted to start the APU so they could use the APU generator for ground power. When the APU master was selected 'on' the 'APU fail' caution message was displayed on the EICAS. The captain and I elected to MEL the APU under 49-1. There was already an MEL open on the APU bleed system issued under MEL 36-6. MEL 49-1 can be issued provided MEL's 36-1; 36-3; nor 36-4 have not been issued in conjunction with this MEL. The MEL was issued and crew placarded.

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Original NASA ASRS Text

Title: EMB145 IS DISPATCHED WITH INCOMPATIBLE MEL'S THAT GROUND THE AIRCRAFT UPON ARRIVAL AT DESTINATION. LACK OF CROSS REFERENCING IN MEL BOOK IS CITED AS CAUSE.

Narrative: DEPARTED WITH MEL 36-6 ISSUED FOR APU BLEED VALVE. AFTER WE ARRIVED IN ZZZZ; WE ATTEMPTED TO START THE APU FOR ITS GENERATOR. WHEN THE APU MASTER KNOB WAS MOVED TO 'RUN' POSITION; THE 'APU FAIL' MESSAGE WAS DISPLAYED ON EICAS. I CONTACTED DISPATCH WHO THEN STARTED A CONFERENCE CALL TO MAINT CTL. I DESCRIBED THE SITUATION TO THE MAINT CTLR; WHO THEN ISSUED MEL 49-1 TO DEFER THE ENTIRE APU. MAINT CTL; DISPATCH; AND I FAILED TO NOTICE THAT MEL 36-6 CANNOT BE IN EFFECT WITH MEL 49-1. DISPATCH INFORMED US ENRTE ABOUT THE DISCREPANCY. THE XREF BTWN THE MEL'S WAS ONLY MARKED FOR MEL 36-6; AND NO ONE THOUGHT TO LOOK AT THE EARLIER ISSUED MEL. TO HELP AVOID A SIMILAR EVENT IN THE FUTURE; IT WOULD BE HELPFUL TO HAVE MORE COMPLETE XREFING OF MEL'S. IN ADDITION; A MORE CAREFUL REVIEW OF ALL ISSUED MEL'S WOULD HAVE CAUGHT THE ERROR. SUPPLEMENTAL INFO FROM ACN 810286: DISPATCHER WORKING THIS ACFT ON NEXT FLT LEG CAUGHT MEL DISCREPANCY AND BROUGHT IT TO MY ATTN. I CONTACTED MAINT CTLR WHO ORIGINALLY ISSUED MEL WITH ME. HE; IN TURN; REVIEWED MEL BOOK WITH HIS SUPVR. I REVIEWED MEL BOOK WITH MY SUPVR AND ADVISED CREW (VIA ACARS) OF DISCREPANCY. MY SUPVR SENT AN EMAIL TO FLT DEPT REQUESTING MEL BOOK CORRECTION/CLARIFICATION. MAINT CTL SUPVR ALSO REQUESTED CORRECTION/CLARIFICATION FROM FLT DEPT. SUPPLEMENTAL INFO FROM ACN 810293: CREW ANTICIPATED A SLIGHT DELAY IN OBTAINING GND PWR. THEY ATTEMPTED TO START THE APU SO THEY COULD USE THE APU GENERATOR FOR GND PWR. WHEN THE APU MASTER WAS SELECTED 'ON' THE 'APU FAIL' CAUTION MESSAGE WAS DISPLAYED ON THE EICAS. THE CAPT AND I ELECTED TO MEL THE APU UNDER 49-1. THERE WAS ALREADY AN MEL OPEN ON THE APU BLEED SYSTEM ISSUED UNDER MEL 36-6. MEL 49-1 CAN BE ISSUED PROVIDED MEL'S 36-1; 36-3; NOR 36-4 HAVE NOT BEEN ISSUED IN CONJUNCTION WITH THIS MEL. THE MEL WAS ISSUED AND CREW PLACARDED.

Data retrieved from NASA's ASRS site as of May 2009 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.