B767 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 250; Flight Crew Total 20000; Flight Crew Type 15000
Confusion; Human-Machine Interface
ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Air Traffic Control Issued Advisory / Alert; Flight Crew Returned To Clearance; Flight Crew Diverted; Flight Crew Became Reoriented
Aircraft; Company Policy; Human Factors
Flight plan loaded [prior to departure]. All class II procedures followed; route and waypoints all checked by SOPs.  One NAT X waypoint was N48 W050. On check in with Gander Domestic; cleared direct 48 N  50 W.   PF [Pilot Flying] selected; and made NICSO; the only intermediate waypoint; an abeam.  Confirmed 50W time and next waypoint with Gander. Passing abeam NICSO; did a class II waypoint check.  Next waypoint; N48W050; estimated XA11; howgozit time was XA09.  Course was close; not expected to match because we were abeam NICSO; not overhead. Distance matched within a few miles. Followed all normal class II SOPs; checked in with Gander Oceanic; etc. Approaching 50W; began waypoint SOPs; got CPDLC to call Gander domestic on VHF. Controller advised we were 12nm north of 48/50. Checked waypoint; still read N48W050.  All GPS on position page dead on. Passed 50W waypoint; and position report page switched. Instead of reporting pos shown as N48 W050; it showed N4812.3 W5006.3. All other oceanic waypoints checked by bringing shorthand (N50 W040) down to scratchpad to expand to lat /long.  All were correct.Gander domestic turned us back to YYT to troubleshoot; but did say that radar showed our course to 50N40W looked accurate.  Captain brought back from break; contacted Maintenance control and Dispatch. Examined all possibilities; consensus was that N4812.3 W5006.3 was loaded into FMS by Sabre uplink; but shorthand showed N48W050.  None of the class II SOPs will detect this type of error. Captain / Dispatcher made decision to continue; but fuel stop was required; as arrival fuel now projected at 6.0.
The OFP showed our filed oceanic track as X. I independently verified the track waypoints on the OFP with the track message; and the FOs [First Officer] did the same together and circled each waypoint during the flight planning process. One First Officer plotted the route on the Atlantic chart. At the aircraft the route was automatically uploaded into the FMC and verified by all three pilots. I copied the route from the FMC into the Jepp FD-Pro application on my iPad. During flight; the oceanic clearance request was sent approximately 1:15 prior to reaching the oceanic entry point of NICSO. We received the oceanic clearance exactly as requested - Track X; FL350 and M.80. When the oceanic clearance was received; the PM [Pilot Monitoring]; read the waypoints from the clearance and I verified each waypoint and put a slash through it on the Master FP as it was read.En route to NICSO; Gander ATC asked us our estimate for 48degN; 50degW and to verify the following point; which was 50degN; 40degW. This is a routine request from Gander on all oceanic crossings and we complied with the request. Shortly after that; we were cleared directly to 48degN; 50degW which is also routine with Gander ATC at this point. On the FMC LEGS page I selected/executed direct to 48degN; 50degW and selected ABEAM PTS to get a fuel and time reading abeam NICSO. Shortly after this it was time for my break and the IRO came back to the Flight Deck and the switch was made. Not long into my break I was summoned back to the Flight Deck.When I arrived back on the Flight Deck; we had recently passed both the abeam point for NICSO and the 48degN; 50degW waypoint. However; Gander ATC had called and told us that they showed us 12nm north of the 48degN; 50degW waypoint and would not allow us to proceed any further into oceanic airspace until we could explain the error and assure them that we did not have a navigational issue. At the time; we told them we were unsure why they were showing this course error; so we complied with their request to make a 180 deg turn back towards Canadian airspace. As a safety precaution I turned on all of the aircraft's exterior lights as we made a left turn from our current heading of approximately 095 deg to the assigned heading of 275 deg. We never exceeded the 25nm limit for a Gross Navigational Error and were in radar contact with Gander ATC the whole time. I had the IRO call the Flight Attendants during the turn and assure them that our problem was a navigational issue and not a mechanical; weather or security issue and that we would get back to them with more information when we had time. The position report for 48degN; 50degW in the FMC showed that we crossed this point at N48deg12.3' and W50deg06.3'. This didn't make sense to us as the oceanic waypoints were verified at least four times prior to our entry into oceanic airspace. Plotting is no longer required; but we plotted our course from the position report coordinates and confirmed that we were about 12nm north of course. After our turn Gander asked us our intentions; and we requested and were granted a clearance direct to YYT VOR to hold. They descended us to FL320 for traffic; we slowed the aircraft to M.74 and proceeded to the VOR and entered the hold.While heading to the VOR; we set up communication with our Dispatcher via SATCOM. He added a maintenance technician to the conversation and we discussed the issue with both of them. We had no flags; warnings; EICAS or STATUS messages and all navigation systems seemed to be operating normally. Both of our GPS positions were showing 0.0 and the IRUs were showing from .5 to 2.2 off; but we were navigating via GPS. We verified with Dispatch that the route had been loaded correctly - specifically asking about the oceanic waypoint entries - and discussed options. The maintenance technician suggested that we cycle a circuit breaker for one of the GPS units; but since both of those units were showing 0.0; we chose not todo that. The three of us repeatedly checked all of our navigation equipment; discussed numerous route and landing options/scenarios; and there was good CRM as we talked about mechanical issues; navigation issues; fuel requirements; weather forecasts; FAR 117 limitations and more.From all of our discussions and troubleshooting; it appeared that the only issue was that somehow the FMC had computed or uploaded the incorrect lat/long for 48degN; 50degW as N48deg12.3' and W50deg06.3'. FO scratch-padded the subsequent oceanic waypoints and they all showed the exact lat/long of each waypoint per the OFP. As we passed over YYT VOR; Gander ATC verified that we were exactly over the VOR. At that point; we determined that there was most likely an upload error/software glitch at the 48degN; 50degW waypoint on our oceanic route. We chose to head back towards Europe and determine a course of action once headed eastbound. We kept Dispatch on the line and discussed landing in either ZZZZ or ZZZZ1 . Gander re-cleared us via Track X at M.80; FL360 and we headed back out onto the oceanic track. Before Gander terminated radar service we asked them once more if they showed us on a correct track towards the next waypoint and they said that they did. The time from our turn back to a westerly heading to the point at which we determined that it was most likely an FMC upload/computational error at that waypoint and headed back to 48degN; 50degW; had been approximately 45 minutes.After we reprogrammed the FMC to continue; it initially showed us landing with fuel of 5.9; then decreased to 5.6 a few moments later as we made some minor adjustments to our speed in the FMC. The TAF for ZZZZ2 (which we had Dispatch verify for us again) was for IFR conditions: TEMPO 2603/2610 4500 -RADZ BKN008. This was not enough landing fuel for these conditions; so we discussed the situation with Dispatch and decided to divert to ZZZZ1 to refuel.I re-programmed the FMC for ZZZZ1 and we explained to the Flight Attendants and then the passengers the details of the problem and the plan to proceed to ZZZZ1 for fuel. Crew legalities were checked and we told Dispatch that we would like to refuel as quickly as possible and proceed to ZZZZ2 . He agreed and re-filed us to ZZZZ1 . An ZZZZ1 OFP and weather was uploaded to the ACARS. The rest of the flight was uneventful. We landed in ZZZZ1; refueled and continued on to destination. (The actual weather upon our arrival was lower than forecast. The ceiling was 800 feet overcast and the visibility was less than 2 miles.)
B767 flight crew experiences a track deviation while attempting to navigate direct to 48N50W. While the FMC showed 48N50W; the actual position reported to CZQX was N4812.3 W5006.3. CZQX will not allow the flight to continue and the flight turns back while troubleshooting and discussing with Maintenance Control. Eventually; with no navigational anomaly detected the flight is allowed to continue on NAT X with a fuel stop.