Date: 201710
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Aircraft: B747-400
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Taxi
ATC / advisory: Ramp ZZZ
Aircraft component: Flight Crew Harness
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Relief Pilot
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown
Second reporter function: First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Maintenance
Detector: Person Flight Crew
When detected: Taxi
Result: General Maintenance Action
Contributing factors: Human Factors; Aircraft; Incorrect / Not Installed / Unavailable Part
Primary problem: Incorrect / Not Installed / Unavailable Part

Narrative: Flight pushed out on time. Captain was PIC (Pilot In Command) in the left seat; First Officer as PM (Pilot Monitoring) in the right seat; [myself a relief Captain] in the middle observer seat and a [Relief] First Officer in the left observer seat.While still hooked up to the tow tug; abeam [the] gate and with two engines started; [the Relief] First Officer encountered trouble with his 5 points quick release harness (hard to close and extremely difficult to release. It would not release via quick release tab and took extreme force tugging on the belt to release it). Relief First Officer communicated the issue and I confirmed the troublesome operation of his belt. Captain asked on headset for Maintenance to come back onboard via the E&E door. Maintenance confirmed the problem with the belt and left the aircraft to secure a borrowed belt. The cockpit crew coordinated with ATC to stay put until a decision was made to either continue; or return. The (Dispatch Deviations Guide) DDG was checked for possible relief; which the DDG did not offer (Most Observer Seat equipment can be deferred; but the seatbelts and O2 are not part of it. A note makes it the PIC decision based on safety and; as was decided by the Captain; the non-functioning seatbelt was unequivocally a required safety item). He called Maintenance Control Center (MCC); Both MCC and local Maintenance agreed a return to the gate was warranted. It appears the installed belt was the wrong part and the tab was thicker than the other belts; was of a different geometry and with squared hole and tab in lieu of the required rounded tab and round hole. See attached picture of placards on correctly installed belt on trouble-free middle observer seat versus picture of placard on removed belt from left observer seat.Maintenance provided [the] Captain with the signed-off logbook; The corrective action was clearly in contradiction with the observed performed Maintenance action as it stated 'cleaned mechanism of debris ops check normal' when the belt portion was actually replaced. [The] Captain declined the logbook based on the misleading corrective action. Maintenance brought back the logbook with the original incorrect corrective action lined through and the new corrective action properly annotated underneath (See attached copy of logbook page). Captain accepted the Logbook sign-off and the flight departed. [Flight Operations] called [the] Captain directly on his personal phone to inquire as to the reasons for the BTB (Block Turn Back).


Second narrative: [Report narrative contained no additional information.]


Synopsis: B747 flight crew reported that the seatbelt/harness for the second observer seat did not release properly; and that Maintenance initially failed to accurately document the repair.