FAA Recommends Boeing 777 Autothrottle Wiring Repair

Credit: Nigel Howarth / AWST

The FAA is urging Boeing 777 operators to modify wiring to eliminate the risk of uncommanded throttle advances while aircraft are on the ground.

Boeing in 2015 issued a recommended fix for the issue, which has led to several in-service incidents.

“The majority of events occurred during taxi, and in one event the autothrottles advanced after landing before the speed brakes were retracted,” the FAA said in a non-mandatory special airworthiness information bulletin issued June 11. “Investigation revealed that these events were probably caused by a short between grounding wires to the [takeoff/go-around] switches. When this occurs, the aircraft senses the . . . switches have been pushed, the autothrottles activate in [thrust-reference] mode and the thrust levers advance to set takeoff thrust.”

The recommended repair is to change the grounding wires, the FAA said.

Boeing in March 2019 issued a flight-crew bulletin that explains how pilots can monitor thrust-lever movement and prevent uncommanded changes.

The issue is not severe enough to warrant a mandatory change via an airworthiness directive, the agency said.

Sean Broderick

Senior Air Transport & Safety Editor Sean Broderick covers aviation safety, MRO, and the airline business from Aviation Week Network's Washington, D.C. office.