777Uncommanded Autothrottle Advance on Ground

[tcasblue]

A bit more detail now on why it was happening. Seem to remember that one was supposed to always have a hand on the thrust levers after the initial advisory. If I remember correctly, I think TOGA will only activate with flaps extended.

"The FAA (https://aviationweek.com/awin/company/31159) is urging Boeing 777 (https://aviationweek.com/awin/program/638) operators to modify wiring to eliminate the risk of uncommanded throttle advances while aircraft are on the ground.

Boeing (https://aviationweek.com/awin/company/12083) 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 (https://aviationweek.com/awin/company/31159) 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 (https://aviationweek.com/awin/company/31159) said.

Boeing (https://aviationweek.com/awin/company/12083) 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."

[Judd]

It always had me tossed why in the 737 Classics, Boeing switched the autothrottle switch to ARM before starting the engines. Previously, the autothrottle was switched to ARM only when lined up for takeoff. This was a precaution against an inadvertent touching of the a TOGA switch while taxiing which could prove disastrous on the tarmac or taxiing behind another aircraft. . A wise flight safety precaution one would have thought?

[Monty Niveau]

Judd, not just that, but if this procedure was applied intelligently, the system was armed on receipt of takeoff clearance. So, it served as a useful confirmation that clearance had been received. Pressed TO/GA and nothing happened? Check with tower that you’ve received your clearance... A rare intersection of good HF science and aircraft operations.

Boeing’s method is like carrying a hunting knife tucked in your belt, when you’ve a perfectly good sheath for it the other side. There are no arguments whatsoever for arming until ready to get airborne.

[Papa_Golf]

Same bulletin was there for the 737NG in my previous company. The airline procedure was to arm the autothrottle just before entering the runway, to avoid the risk completely.

My current 777 outift doesn’t deviate from Boeing suggested procedures. It happened once that the AT engaged to TOGA without pilot input. Having the hand on the throttle actually helped.