Narrative:

ATC gave us a 10 degree left turn, at the time we were using FMS (LNAV). The heading switch and the VNAV switch are next to each other. I must have hit the VNAV switch at the same time I pushed the heading switch. We noticed the altitude change as we were passing 31250 ft. The autoplt was kicked off and a recovery to 31000 ft was started. The maximum altitude we reached was 31300 ft.

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Original NASA ASRS Text

Title: ALTDEV. EXCURSION FROM ASSIGNED WHEN SELECTING HDG SELECT AND INADVERTENTLY HITTING THE VNAV SWITCH. ACFT CLBED 300 FT, FLC SAW IT AND RETURNED TO ASSIGNED.

Narrative: ATC GAVE US A 10 DEG L TURN, AT THE TIME WE WERE USING FMS (LNAV). THE HDG SWITCH AND THE VNAV SWITCH ARE NEXT TO EACH OTHER. I MUST HAVE HIT THE VNAV SWITCH AT THE SAME TIME I PUSHED THE HDG SWITCH. WE NOTICED THE ALT CHANGE AS WE WERE PASSING 31250 FT. THE AUTOPLT WAS KICKED OFF AND A RECOVERY TO 31000 FT WAS STARTED. THE MAX ALT WE REACHED WAS 31300 FT.

Data retrieved from NASA's ASRS site as of July 2007 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.