B787 Captain expressed concerns regarding application of MEL for a Cabin Air Compressor (CAC) problem that had existed for a number of days for what he learned was a history of burnt contractor pins. The Captain spent hours working with Maintenance and Dispatch with crew duty time limits in the background to depart with contingency plans for flight only to have flight be unexpectedly cancelled during taxi out.

Narrative

Log history had several days of repeated write-ups for right Cabin Air Compressor (CAC) faults and right Pack trips and resets. The inbound flight had several log entries relating to intermittent Right Pack EICAS Advisory messages; including one failed reset airborne per the Emergency Checklist.On arrival of the inbound flight; local Maintenance worked to reset associated air system status messages; and the flight was dispatched with a MEL for an R1 CAC deferral to operate with a single right CAC.The flight blocked out at XG:17Z (12 minutes late). During the first taxi-out; the Right Pack failed; with an associated EICAS Advisory and Emergency Checklist. This procedure allows a single attempt at a Pack Reset; which was accomplished. Within 2 minutes of Emergency Checklist completion (prior to takeoff) the Right Pack Advisory EICAS message returned. Dispatch and Maintenance Control were consulted via SATCOM; and Maintenance Control determined that the R2 CAC had surged; which resulted in a CAC fault and shutdown and resultant trip of the associated Pack. Maintenance Control directed a return-to-gate would be required for maintenance action.A return to the gate was effected..For several hours; Maintenance trouble-shot the CAC/Pack issues. Ultimately; they were able to reset the R1 CAC; but determined that the R2 CAC was determined to be faulty. During this extensive delay; Conversations between the flight and dispatch continued; and by Dispatch noted that additional fuel would be required (B343 5 percent vice B343 fuel reserves due to falling out of the window). I directed that we hold off on Release 2 fuel planning until we knew what MEL deferral we would be operating under.Soon after; the dispatcher would be engaged in a medical emergency with another flight. With that in mind; I initiated a SATCOM conference call between the Chief Pilot and Maintenance Control; to explore options of continuing with a single CAC deferral or possible courses of action should the Right Pack fail again after pushback (but prior to takeoff) or airborne after takeoff. After extensive discussions; it was determined that if the Right Pack should become INOP after pushback; that maintenance action would be required in order to continue (under MEL XXXXXX) which would necessitate another gate return. However; when the Right Pack is deferred under MEL YYYYYY this refers to MEL Card ZZZZ; which includes under Special Notes: J. Flight remains within 60 minutes of landing at suitable airport.This limitation negates flight into ETOPS; which made deferral of the Right Pack unsuitable for the operation. With this information; Dispatch ; Chief Pilot; Maintenance Control and myself concurred that we would dispatch with the R2 CAC deferred (under MEL); and should the pack fail following pushback and prior to takeoff; the flight would require a return-to-gate again; with a probable cancellation due to the above-noted non-ETOP limitation (and probable crew timeout). With all parties in agreement; a new release was subsequently planned and signed; a revised fuel load obtained; and a new Maintenance Release obtained and validated.The flight pushed back again; and during the push sequence and engine start; the single right CAC was holding steady.As pushback was completed with engines started and the ground crew awaiting a Cleared to Disconnect call from the Captain; the flight received the following messages on the printer (in order):XA:10Z Final CCO (Critical Crew Off time) Message (Duty CCO Time XA:54Z)XA:11Z Disptach: "Captain. Maintenance Control leadership has taken your aircraft out of service to be fully repaired in ICN. I am in the process of cancelling your ATC flight plan."XA:14Z : "Based upon your projected ETA for this flight your FDP (Flight Duty Period) may require an extension that is allowable under Part 117 with PIC's concurrence. PIC; please confirm with MISC the ability to extend (ACARS Message "able to extend").XA:17Z Final Weight MessageXA:17Z EXPECT NEW Maintenance Release ALERT:****DO NOT TAKE OFF****"Maintenance is working with the following item. Expect a new Maintenance Release and do not push back without it.ITEM: Based on history of both R1 and R2 CAC Faults with associated Pack shut down - Maintenance to accomplish further troubleshooting of right pack system. More direction to follow"I was not made aware of these messages until the parking brake was set ;due to sterile flight deck procedures. Once the content of these messages was made clear; I directed the ground crew to remain connected; and then initiated another SATCOM conference call between Dispatch; the Chief Pilot and the Maintenance Control controller; who related that Maintenance leadership had directed the cancellation of the Maintenance Release and the return to the gate.A return to the gate was effected with a block-in at XA:29Z.(Issues regarding facilitation issues on the flight cancellation will be covered separately.)Subsequent contacts with the Chief Pilot were made to effect crew accommodations and transportation; and following arrival at the hotel; follow-up between the Chief Pilot and the Captain about crew legalities for follow-on operations; and the decision-making process and intervention by Maintenance leadership.In this last area; there are three concerns I have:First; with extensive conversations; threat analysis and mitigation; the principal parties to the operation - Maintenance Control Line Controller; Dispatch; Chief Pilot and the Captain-in-Command - had all agreed to a course of action that was in accordance with our SOP and Maintenance publications; specifically; the 787 MEL. In spite of four full hours of thoughtful and considered coordination; someone outside of this circle decided to come to work; read an email and make a unilateral decision to intervene. Where what his person in the four hours prior? This raises the concern that the four aforementioned parties to the operation; myself included; somehow failed to ascertain a threat to the operation. If so; WHERE is this person and why don't we have a debrief on the decision-making process and how that process FAILED?Second; we in flight standards (LCPs) (Line Check Pilot) go to great lengths to preach that an operation that conforms to allowances published in a MEL should be honored unless there are extenuating circumstances; and that refusing to operate in spite of a valid MEL should not be taken lightly. In this operation is considered by all parties; yet someone not a direct party to the operation; decided to go countermand our SOP and weigh in 10 minutes prior to takeoff. Third and finally; upon follow-up conversation with Maintenance Control; it was determined that the underlying cause of the CAC faults are that contractor pins to the CAC power supply (my own understanding; I don't know the exact nomenclature of the failed component) were burned; and had been failing. This now brings us to the larger issue of the decision to keep this aircraft in service for several days; in ETOPS operations with these known; repeated discrepancies. This revelation now further jeopardizes the validity of our MEL guidance."