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A new airworthiness directive issued by the US Federal Aviation Administration requires Boeing 777 operators to inspect and potentially replace the aircraft's dual pitch rate sensors (PRS).
The directive, which applies to 777-200LRs, -300s, -300ERs and 777 freighters, comes in response to reports received by the agency of dual failures of the sensors.
When both sensors fail, the aircraft's primary flight computer transitions from primary to secondary mode, which causes the autopilot to disengage, says the directive, made public by the US Office of the Federal Register on 19 November.
"We are issuing this AD to prevent a dual PRS failure that could cause an automatic disengagement of the autopilot and autoland," says the DOT's directive.