2011-05 · NASA ASRS report 951674
A B777 flight crew experienced engine thrust advancing to maximum as the Captain attempted to turn onto the parallel taxiway after landing. The brakes were quickly applied and thrust levers retarded. It was necessary to disarm the auto-throttles to prevent the throttles from advancing again.
[We] turned off at Taxiway K-4 per Tower instructions. After turning onto Taxiway K-4 I called for the after landing checklist and removed my hand from the throttles to allow the First Officer to do his flows. I was looking left toward Taxiway K about to begin the turn onto K at a speed of about ten knots. I heard the engines begin to spool up and the airplane started to accelerate rapidly going toward the grass. I immediately brought the airplane to an abrupt stop and reached for the throttles. The throttles had advanced to takeoff/go around power and the engines were at a high thrust. I began to retard the throttles; but the auto-throttles were engaged and were trying to keep the throttles at high thrust. I deselected the auto-throttles with the throttle disconnect switches and retarded the throttles to idle. The auto-throttles had commanded max power but the engines did not exceed any tolerances. The engines had spooled up to a high power setting but it was only two to three seconds before I retarded the power to idle. As the power was increasing we received the takeoff warning oral alerts for flaps and gear alignment. The First Officer had selected flaps up and had moved the speed-brake handle to the retract position. At no time did either of us select the TO/GA switches on the throttles. Prior to landing we had been in moderate precipitation and light icing. Conditions were turbulent with loss and gain of air speeds reported by other aircraft. We had a five knot loss on final. I debriefed maintenance and asked that the tires also be checked for any significant wear due to the abrupt stop in slippery conditions.
After landing and clearing the runway; during the after landing check; the throttles started advancing uncommanded. The Captain retarded the throttles to idle and braked to a stop. We don't know why the throttles advanced; the Captain nor I touched the TOGA buttons or bumped the throttles.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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