Date: 201909
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Aircraft: B767-300 and 300 ER
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
Aircraft component: Hydraulic System Pump
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown
Second reporter function: Captain
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Pre-flight
Result: General Flight Cancelled / Delayed
Contributing factors: Procedure; Aircraft; Company Policy; Human Factors; MEL; Manuals
Primary problem: MEL

Narrative: Our flight had the following deferrals. 21-XX-XX; 29-XX-XX-XX; 49-XX-XX. The 29-XX-XX-XX deferral required the ADP (Air Driven Pump) to be turned on at certain times. The switch was turned on and we had got the C HYD DEM PUMP advisory message and the PRESS light on the hydraulic panel. We called the Local Maintenance on the radio; and found the Air Pump CB (Circuit Breaker) was out. They advised us to push it in; but it didn't solve the problem; and advised us to come back to the gate. When we returned to the gate the maintenance guys said that [Maintenance] was going to defer the whole ADP under 29-XX-XX; which knocks out the HMG (Hydraulic Motor Generator). With the APU deferred you can't have the HMG deferred if it's required. The APU was completely fine; but deferred because the ADP valve was leaking the bleed air; according to the mechanics. They stated that they have been asking [Maintenance] to change the valve for 2 weeks. On our conference with Dispatch; [Maintenance] and the duty pilot they wound up amending the APU deferral to pneumatics only. So; there wasn't a conflict between the deferrals.Once again I believe that this is a case of improper deferrals and undue pressure for crews to take the aircraft to maintain schedule integrity. I understand that the HMG may not have been required per se for our short flight; but when the APU and the ADP deferred we were down 2 back up electrical systems and flying through a line of thunderstorms and forecasted lower ceilings. Why would a perfectly good system be deferred just because another system that can be fixed hasn't been? I think we should be erring on the side of safety; and acting out of an abundance of caution in the current climate.


Second narrative: Upon taxi out when complying with DDG (Dispatch Deviation Guide) 29-XX-XX-XX we got an ADP (Air Driven Pump) press light and an EICAS message was generated. This was not addressed or acceptable per 29-XX-XX-XX. An inoperative ADP was improperly deferred in conjunction with the APU. After gate return 29-XX-XX-XX was amended. Additionally; the APU was deferred with 49-XX-XX. This was due to a faulty air regulation valve as we were told by Maintenance. There seemed to be a conflict within the Deferral regarding necessity of the HMG (Hydraulic Motor Generator) regardless of if we were emergency operations or not.Multiple Deferral- items with multiple (excessive) effectivity made it confusing as to what is required and when. Maintenance Control wanted to argue about the applicability and at one point tried to tell us the RAT (Ram Air) would power the HMG. This did not instill confidence in us that anything they were doing was correct. There needs to be a little more clarity as to what equipment is required when if we are dealing with multiple deferred items with regard to emergency vs non emergency operations. The deferred items were amended and the aircraft was released with the APU deferral was 49-XX-XX minus pneumatic air and the ADP was completely deferred with 29-XX-XX-XX.


Synopsis: B767 flight crew reported multiple and conflicting MELs applied to aircraft requiring extensive review and reapplication caused a significant delay in departure.