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The FAA is evaluating risks posed by incorrectly assembled rudder parts that may be installed in hundreds of Boeing 737s after the NTSB issued what it termed “urgent” recommendations spotlighting the problem.
At issue are 353 SVO-730 rudder rollout guidance actuators supplied by Collins Aerospace starting in February 2017. The actuators contain sealed bearings that were not assembled correctly,the NTSB said in a recommendation letter detailing the issue. The mistake makes the actuator more likely to get wet inside and freeze at altitude. That in turn can jam the aircraft’s rudder system.
At least three in-service incidents have been linked to the condition. An August Multi Operator Message from Boeing said that while the issue does not pose an immediate safety threat, the airframer intends to develop a plan to remove the questionable parts.
In a Sept. 30 letter to FAA Administrator Mike Whitaker, NTSB Chair Jennifer Homendy took issue with Boeing’s response and said she was “disappointed” in the agency’s lack of action. Her letter revealed that 271 of the suspect parts may be in service on aircraft operated by as many as 40 non-U.S. carriers. In addition to the inventory sent to Boeing, Collins shipped another 75 directly to operators as spares, adding an aftermarket angle to the safety risk.
The board urged the FAA to scrutinize the risk the parts pose and to determine whether they should be removed from the fleet, as well as to develop an appropriate response plan that involves non-U.S. regulators.
Investigators discovered the problem while probing an in-service report for a February incident involving a United Airlines 737-8. The pilots reported jammed rudder pedals during a landing rollout at Newark International Airport following an otherwise routine flight from Nassau, Bahamas.
SVO-730 actuators are part of the 737’s fail-operational autoland system with rollout guidance. The system is required for approval to conduct Category III B low-visibility landing operations. United’s 737s do not fly Category III B operations, but it took delivery of nine aircraft built for the highly restrictive operational approval but later reconfigured to match the airline’s needs.
United’s actuators were electrically disabled but remained mechanically linked to the rudder system. The airline was not aware they were installed, the NTSB said.
The board has not determined why the manufacturing error occurred, but information released in the recommendation letter suggests relocated production may have played a role. Deliveries of the incorrectly made parts began just after Collins moved its manufacturing facility from Melbourne, Florida, to Mexicali, Mexico, with all of the problem actuators made in Mexicali.
Part of the NTSB’s urgency stems from concerns about risk posed by the actuator combined with Boeing’s pilot guidance on handling a jammed rudder. The airframer tells pilots to “overpower” jammed or restricted rudder controls, the NTSB said, but the amount of force needed to free a frozen rudder actuator could introduce new hazards.
Boeing and Collins calculated a frozen actuator requires about 87 lb. of rudder-pedal force to move. “However, this amount of force applied during landing or rollout could, in clearing a jam or restriction, also result in a . . . sudden, large and undesired rudder deflection that could unintentionally cause loss of control or departure from a runway,” the NTSB said.
The board also suggested Boeing’s jammed rudder guidance is not specific enough. “[Only] general procedures for jammed or restricted flight controls are provided in the Boeing 737 Airplane Flight Manual and Flight Crew Operating Manual, and the rudder rollout guidance actuator is not mentioned as a potential source for a jam or restriction in the rudder control system,” the report said.
The NTSB’s concerns led it to take two rare steps beyond its FAA-focused suggestions: issuing recommendations directly to Boeing and marking them as “urgent.”
Most NTSB recommendations go to a regulator that can use its legal authority to mandate changes. But in some cases, the board will go directly to the companies involved. The board said Boeing should determine what pilots could do “besides applying maximum rudder pedal force” to free a seemingly stuck rudder, and ensure operators are aware of the scenario.
“A jammed or restricted rudder scenario could become even more concerning [with] a high-crosswind or an engine-out condition,” the board said. This, it added, is “not only because the amount of rudder available to respond to these conditions might be insufficient to maintain control of the airplane if the jam is not cleared—but also because excessive rudder input may result if the jam is cleared by responding with Boeing’s mitigation.”
The FAA said it plans to “convene a corrective action review board based upon the NTSB’s interim recommendations and determine next steps.” It also confirmed that United is the only U.S. carrier with the affected parts, all of which have been removed. The United scenario suggests some operators may have them without realizing it due to customer delivery reshuffling and other orderbook changes.
Boeing stated that it is reviewing the recommendations. “[We] are working with our supplier to develop additional guidance to address the potential condition,” the company added. “We will keep our regulator informed of our progress. We will also ensure flight crews have the appropriate operating procedures.”
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