Operators of Boeing 777s are being instructed to replace force-limiter components which could prevent a pilot’s control yoke being freed in the event of the other pilot’s yoke jamming.
The control yokes of the 777 are synchronised, and the force-limiter assembly normally provides a load path for roll control.
But if one of the yokes jams, applying break-out forces to the other yoke enables the pilot to maintain lateral control.
But last year the US FAA was informed that certain force-limiter assemblies were not breaking out within the maximum design force requirements – with the result that a pilot might not be able to override a jam.
Boeing traced this issue to excessive corrosion-inhibitor used during assembly of the force-limiter, which resulted in the increased break-out force.
The FAA is instructing operators of the type, in a directive effective from 7 March, to replace affected upper and lower force-limiter assemblies with compliant parts, as specified in a Boeing bulletin from October 2021.
Several operators – among them All Nippon Airways, China Airlines, FedEx, Swiss, and United Airlines – expressed concern that long lead times for the updated assemblies would make meeting the 12-month compliance deadline difficult.
But the FAA points out that the replacement requirement is limited to 777s with line numbers from 1531 to 1707 – those on which suspected assemblies were fitted – and aircraft on which the original assembly has been replaced.
It adds that operators unable to meet the deadline can request approval of an alternative means of compliance. The FAA believes just over 350 aircraft on the US registry are affected by the directive.