Date: 201706
Local time of day: 1201-1800
Location: ZZZZ.Airport, FO
Flight conditions: VMC
Aircraft: B777 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Taxi
Aircraft component: Interphone System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer; Relief Pilot
Human factors: Situational Awareness; Training / Qualification
Second reporter function: First Officer; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: Aircraft In Service At Gate; In-flight
Result: Flight Crew Became Reoriented; General Maintenance Action
Contributing factors: Aircraft; Human Factors; Procedure
Primary problem: Aircraft

Narrative: [I] reviewed all flight paperwork. Reviewing the Differed Item List (DIL)/Minimum Equipment List (MEL) document; we noted that there was a deferral for a 'Loud Hum on Flight Interphone'. We noted that we were supposed to use the Ground Service Interphone for Flight Deck to Ground communications. After proceeding to the aircraft; we accomplished all required cockpit preflight duties. After receiving the Release the Captain and flying First Officer (FO) talked about the applicable cockpit deferred items and proper switch location per the flight crew section of the MEL. The crew validated that there was a loud hum in the flight interphone position and placed the overhead inter phone switch to the Service Interphone position. We did engage in a short discussion about how the loud hum might impact us in case of a Fire; Smoke or Fume situation in establishing effective crew communications between the pilots. We felt that while it could be a distraction; we would still be able to communicate. Prior to departure time; ground personnel came to the cockpit to see if we could pull Ground power; at which time we informed them that they would need to plug into the service interphone jack for Ground to flight deck communications. When they plugged in; we experienced a loud hum in the interphone system. The FO tried to communicate with ground personnel but was unable to. Ground personnel and Maintenance came back into the cockpit at which time they communicated that they would use hand signals to push us back. They reviewed hand signals for fire; brake release; brakes set and engine start/shutdown with the Captain. They coordinated that Maintenance would walk with the airplane during push and maintain visual contact with the Captain and the tug driver. Today; they would be using a tug that lifts the airplane vs a towbar push. They also coordinated that we would pass the push clearance and break away area to them via a relay with Ops. After Maintenance and Ground personnel departed the cockpit and all aircraft doors were closed; we finished our Before Push Checklists; verified cabin ready with Flight Attendants (FA); and called for push/start clearance. After receiving clearance from Ramp Control; we relayed to Ground personnel; through ops; that we were cleared to push. At that time; ground personnel had the tug lift the airplane; gave the release brakes signal; the Captain released the brakes; and gave the brakes released signal. The pushback was uneventful. The brakes we set In Accordance With (IAW) with coordinated hand signals. The tug disconnected from the airplane; we were given the cleared to start engine signal and proceeded with a normal start. After being given the all clear signal by ground personnel; we called for taxi and taxied to Runway. Takeoff and climb out were uneventful. [I] went on first break. When I came back; the Captain went on break. The Pilot Flying (PF) (flying FO) and I had a discussion about the number of deferred items the airplane and the length of the Release (eight pages). We also talked about writing up the Service interphone; since it did not work for us; which was contrary to the write up which said it worked normal. We also talked about the proper switch placement on the audio panels when using the Service interphone; since there had been some confusion on the ground. During this discussion we relooked at the Release and also the MEL Document on our Ipads. It was during this review; that we began to realize that even though the MEL; in the SPEC NOTES; talks about 'Alternate procedures are established and used.'; it also said in the Operations Placard Flight Crew section A; the 'Nose gear service interphone must operate normally.' Further researching the Flight Operations Manual (FOM); in Chap 3; Section 50 PUSHBACK/TOW-OUT; we found the warning that 'Pushback without headset communications is prohibited.' Additionally; reviewing FOM; Chap 3 Operating Information; page; Pushback Using Hand Signals; seemsto indicate that pushback with hand signals might be allowed in situations bulleted on page. After the Captain came back from his break; we had a crew discussion about whether we had conducted a proper pushback IAW with the FOM; FOM and MEL. Our discussion became centered around about whether the MEL use of the wording 'Alternate procedures...' allowed for the use of hand signals during pushback and met the criteria of the FOM bullet 'Authorized by MEL' After landing we coordinated for Maintenance to meet us at the aircraft. Working with Maintenance personnel at the nose gear position; we retested both the flight and service interphones and confirmed that neither was working normally.


Second narrative: Aircraft had several MEL items (both cabin and system related 'Do' items). [It] required performance adjustment awareness and crew verification actions. Additionally; Ground to Flight deck Interphone System MEL also required verification and action. During cockpit set up and MEL verification; maintenance was asked to review and agree on use/communications using the Service Interphone function as directed by [the] MEL.Both maintenance and the flight deck crew agreed that the loud humming noise on the flight interphone also negatively impacted communications using the Service Interphone. Maintenance and the flight deck crew agreed that an additional communication method (using the operations frequency to provide a relay (as necessary) via handheld radio with the pushback crew WAS BOTH SAFE AND TIMELY. Maintenance provided additional marshaling assistance (5-6 ground ramp personnel). Upon maintenance request; the flight deck crew reviewed appropriate handling signals with the pushback crew. The pushback was both safe and uneventful.En route; our Flight Crew conducted a review of the Flight Operations Manual (FOM); MEL and Flight Manual as each relates to and influenced BY [the] MEL. Issues we discovered:1) We determined that there was no longer Flight Manual (FM) guidance for using hand signals for pushback in the 777 fleet. 2) The FOM limits hand signals during pushback to narrow body fleets3) The MEL stated that the Service Interphone must work (while it did work; the flight deck to ground portion of Service Interphone communications was not clear during our discussions with maintenance).


Synopsis: B777 flight crew reported that on pushback the interphone was not available for communications. The crew elected to use hand signals; which they later learned were not allowed by their company.