Narrative:

I was contacted by flight operations a day after my flight and was informed that we had operated an inoperative aircraft system contrary to MEL procedures. We arrived at the aircraft for a long haul flight with several items that had been deferred for a couple of days on our maintenance release. Two of the inoperative systems dealt with the aircraft air systems. The first item was a failed L1-cac (air compressor) and the other was an inoperative l-acm (air cycle machine pack). With the L1-cac; the main thing that stood out was that we were going to be limited to a maximum altitude of 35;000 feet since we were required to use the crew rest. Then there was a list of required equipment. With the inoperative l-acm; there was essentially the requirement that the opposite (r-acm) system was operating normally. This MEL's notes stated how the pack would be off on the ground and operate in standby cooling at the appropriate altitude. After about a ten-minute discussion with the other crewmembers we felt that we had figured out what was required to operate the flight. I feel that the discussion over the two MEL's became very confusing since we had to jump back and forth between the two MEL's that involved the same aircraft systems with a lot of long similar verbiage. I later contacted maintenance control with a text message through the ACARS to get further guidance and the message we received back from them gave us the impression we were correct in our assumptions. Now; with benefit of hindsight and more time to review it appears that we had over looked the l-acm operating in standby cooling did not meeting the requirements of the MEL for the inoperative l-cac. If we had better used the resources available to us of company maintenance at the airport or to a greater degree spoken directly to maintenance control over a landline or by satcom and made further inquiry we would have eliminated the confusion and averted what transpired. I also feel that since this MEL situation was also overlooked by maintenance control and dispatch; it would be helpful if there was a way to improve the verbiage for this and other types of MEL's that cause confusion or possibly develop a means of flagging similar situations when there is a conflict between two MEL's.

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Original NASA ASRS Text

Title: B787 flight crew reported that the information for two deferrals for the same system were very confusing.

Narrative: I was contacted by flight operations a day after my flight and was informed that we had operated an inoperative aircraft system contrary to MEL procedures. We arrived at the aircraft for a long haul flight with several items that had been deferred for a couple of days on our Maintenance Release. Two of the inoperative systems dealt with the aircraft air systems. The first item was a failed L1-CAC (Air compressor) and the other was an inoperative L-ACM (Air Cycle Machine Pack). With the L1-CAC; the main thing that stood out was that we were going to be limited to a maximum altitude of 35;000 feet since we were required to use the Crew rest. Then there was a list of required equipment. With the inoperative L-ACM; there was essentially the requirement that the opposite (R-ACM) system was operating normally. This MEL's notes stated how the pack would be off on the ground and operate in standby cooling at the appropriate altitude. After about a ten-minute discussion with the other crewmembers we felt that we had figured out what was required to operate the flight. I feel that the discussion over the two MEL's became very confusing since we had to jump back and forth between the two MEL's that involved the same aircraft systems with a lot of long similar verbiage. I later contacted Maintenance Control with a text message through the ACARS to get further guidance and the message we received back from them gave us the impression we were correct in our assumptions. Now; with benefit of hindsight and more time to review it appears that we had over looked the L-ACM operating in standby cooling did not meeting the requirements of the MEL for the inoperative L-CAC. If we had better used the resources available to us of company maintenance at the airport or to a greater degree spoken directly to Maintenance Control over a landline or by SATCOM and made further inquiry we would have eliminated the confusion and averted what transpired. I also feel that since this MEL situation was also overlooked by Maintenance Control and dispatch; it would be helpful if there was a way to improve the verbiage for this and other types of MEL's that cause confusion or possibly develop a means of flagging similar situations when there is a conflict between two MEL's.

Data retrieved from NASA's ASRS site 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.