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.

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Original NASA ASRS Text

Title: 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.

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.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.