FAA Has Received Reports Of Uncommanded Autothrottle Advancement

This Special Airworthiness Information Bulletin advises registered owners and operators of The Boeing Company Model 777 airplanes of the potential for uncommanded autothrottle advancement during ground operations. At this time, the airworthiness concern is not an unsafe condition that would warrant airworthiness directive action under Title 14 of the Code of Federal Regulations (14 CFR) part 39.

The FAA has received reports of uncommanded autothrottle advancement (throttles advanced from idle) during ground operations. The majority of events occurred during taxi, and in one event the autothrottles advanced after landing before the speedbrakes were retracted. Investigation revealed that these events were probably caused by a short between grounding wires to the TO/GA switches. When this occurs, the aircraft senses the TO/GA switches have been pushed, the autothrottles activate in THR REF mode, and the thrust levers advance to set takeoff thrust.

Boeing has issued Service Bulletin 777-22-0038, dated December 08, 2015, to provide operators with instructions for a takeoff/go-around switch ground wire change for the autopilot flight director system. Boeing also issued Flight Crew Operations Manual Bulletin TBC-142 R2, dated March 21, 2019, which provides operating instructions to monitor the movement of the thrust levers and prevent thrust from advancing during an uncommanded autothrottle advancement.

The FAA recommends that all owners and operators of the affected airplanes incorporate the actions outlined in the referenced service information at the earliest opportunity.

FMI: www.faa.gov, www.myboeingfleet.com