NTSB Says Rudders Can Freeze In Hundreds of 737s
Moisture seeping into actuators the cause.
The NTSB says the rudders on "more than" 353 Boeing 737NG and MAX aircraft can freeze stuck and it's suggested the manufacturer come up with a solution besides stomping on the pedals to free them up. The board issued an urgent safety recommendation Thursday resulting from its investigation of an incident in Newark last February in which the rudder pedals jammed on a United MAX after landing. The pilots couldn't budge the rudder so the captain kept the plane on the runway using the tiller.
The investigation determined that moisture can get inside the rollout guidance actuator which is only used during CAT IIIB approaches but remains mechanically attached to the rudder controls all the time. In cold weather, the water seeping in through a faulty bearing freezes inside the actuator and hampers the pilots' ability to control the rudder. Collins makes the actuator and has told Boeing about the problem.
The board is suggesting the faulty actuators be removed (presumably limiting low visibility operations) until freeze-proof units can be installed. The board says the flight manual tells pilots with a stuck rudder to “overpower the jammed or restricted system [using] maximum force, including a combined effort of both pilots,” which could make matters worse by resulting in a sudden full deflection of the rudder. It's urging Boeing to come up with another plan for pilots facing a stuck rudder.
