Date: 201511
Location: KZAK.ARTCC, HI
Flight conditions: VMC
Weather elements / visibility: Thunderstorm
Aircraft: B777 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Cruise
Airspace: Class A KZAK
ATC / advisory: Center KZAK
Aircraft component: FMS/FMC
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Confusion
Second reporter function: First Officer; Pilot Flying
Anomaly: ATC Issue All Types; Deviation - Track / Heading All Types
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

Narrative: While I was sleeping on my rest break First Officers were in the cockpit. They had been cleared by SFO via Controller/Pilot Data Link Communications (CPDLC) to deviate around thunderstorms up to 30 miles left or right. They were already in the process of deviating 25 left of flight planned course. Additional weather appeared ahead and they used the parallel course function of the FMC to discern whether further deviation clearance would be required. After determining it was not; they went to clear the parallel course from the FMC but selected ENTER instead of DELETE. Seeing their error; they quickly corrected it; activating the original cleared flight plan. Since the aircraft was in heading mode; no course deviation occurred. ATC soon sent them messages asking why they were right of course. They were not. They were left of course on a cleared weather deviation. ATC must have miss-interpreted the erroneous position report automatically sent when the erroneous left of course offset was activated; disregarding subsequent position reports and free text messages. All this took place while trying to deviate between thunderstorms and communicating with flight attendants. After numerous text messages with ATC it became evident that there was confusion on their part as to the CPDLC they had issued and the flight was adhering to. Their confusion was obviously caused by an erroneous FMC entry by my relief pilots while operating in heading mode that was immediately corrected.


Second narrative: I was pilot flying and circumnavigating thunderstorms with a clearance to deviate 30 miles left or right of course. We were approximately 25 miles left of course using heading select for roll mode.We received a CPDLC uplink asking 'Are you requesting a deviation more than 30 right of course?' We had not. We received a second uplink saying 'Your ADS is reporting a different next waypoint greater than your cleared; deviation; it looks about 50 nm off of filed route.'The other First Officer and I spent several minutes trying to understand why KZAK thought we were right of course and why we might need more than thirty miles deviation. All flight planning and position checks confirmed left of course and within our clearance limit. In fact; at no point had we deviated right of course since receiving the clearance. We had several exchanges with KZAK attempting to clear the confusion; including accepting a 50 nm left and right clearance to deviate; then we were handed over to NFFF FIR. Shortly thereafter; the other First Officer pointed out what may have been the reason for the confusion. Shortly before the uplinks from KZAK occurred; I entered an un-executed route offset of L40 into the FMC to see if I might need additional course deviation left of course due to thunderstorms ahead. After determining I would not need further deviation; instead of deleting the L40 I accidentally pressed execute. I immediately corrected the error by deleting the 40 mile deviation; correcting back to our original course and re-executed. Since I was not in LNAV; nor changing roll modes between LNAV and heading select; and we were still miles to our next position report; it didn't occur to me at the time that a position report would be sent causing confusion over our actual routing. When I executed the L40 it would have sent a report depicting us right of course; the down line waypoint would be changed; and since we were slightly left of our actual routing it would have looked like we were more than 30 nm right of course. It also explains the correspondence with KZAK. Even though I immediately corrected the programming error in less than thirty (30) seconds; and a correct position report should have been immediately sent; it obviously caused some confusion and concern for everyone involved.While I believe this was the cause I am not completely certain as we were never able to completely solve with KZAK before we were handed off to NFFF. We did attempt to contact KZAK via HF; but the hand off had already occurred. It appeared to us at that point that; KZAK was satisfied with our routing and clearance to deviate.


Synopsis: B777 flight crew reported accepting a left 30 NM for thunderstorms from KZAK via Controller/Pilot Data Link Communications. While flying the offset a left 40 was entered to see if more deviation was necessary; then entered instead of being deleted. The left 30 was quickly reestablished but not before the CPDLC sent some erroneous waypoint and track information; causing great confusion at KZAK and with the crew.