Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Flight Crew Last 90 Days 150; Flight Crew Type 1470
Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Unstabilized Approach; Inflight Event / Encounter Weather / Turbulence
Flight Crew Executed Go Around / Missed Approach
Aircraft
EWR had low ceilings and shifting winds. The 4R was out of service; and RNAV approaches were advertised on the ATIS. We prepared and briefed the RNAV (RNP) Z 4R; as the minima were lowest; to better ensure seeing the runway at or before minimums. The autoflight and VNAV functions worked normally until passing the FAF. Upon passing the FAF; and as the winds aloft were shifting towards a headwind; VNAV PTH remained displayed; however the aircraft did not descend; despite touchdown zone altitude being set in the altitude window; per procedure. Indeed; all 3 of us noted that the Captain PFD showed us as being below the vertical path; whereas mine showed being above. The vertical path deviation indicators rapidly diverged and the aircraft remained at 1700 FT as we progressed toward the runway. This was obviously unacceptable; exceeding tolerances; and as such we elected to conduct a missed approach and informed ATC. We subsequently briefed and flew the ILS 4R GS out of service; using LOC and VNAV. This approach was uneventful.
I was in the jumpseat for the RNAV RNP Z 4R. Per the QRH briefing; we briefed if aircraft deviates outside of limits on the vertical path of +75 FT on prog page 2; it is an automatic disqualification for the approach criteria and necessitates a go-around. On the approach; the autopilot deviated from the vertical path by +75 FT and caused us to go-around per the briefing in the QRH.
B767 First Officer and Relief Pilot reported executing a go-around at EWR when the autopilot failed to track the vertical path accurately.