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The FAA is not moving quickly enough to address risks posed by non-conforming parts on hundreds of 737s, NTSB Chair Jennifer Homendy said in a Sept. 30 letter to the agency's top official.
"Although our investigation is ongoing, I am disappointed that it does not appear that the FAA has initiated urgent actions to address the risk of jammed rudder controls in the six months since our preliminary report on this incident was issued," Homendy wrote." The case for urgent action is even greater since, after we opened our investigation, the FAA became aware of two similar incidents that had occurred with foreign operators in 2019."
NTSB's letter comes five days after it issued "urgent" safety recommendations to the FAA and Boeing about the parts, Collins Aerospace-supplied SVO-730 rudder rollout guidance actuators, which can cause a jammed or restricted rudder.
The recommendations--removing the parts, ensuring they don't pose unacceptable risks until they can be removed, and making pilots aware of the hazard and appropriate responses--stem the probe of a February 2024 incident involving a United Airlines (UAL) 737-8. The NTSB's recommendation letter urged the FAA to assess the risk to the fleet and collaborate with foreign regulators that may need to take action.The FAA said United is the only U.S. operator with affected actuators and all have been removed from service.
Boeing in an August message to operators said Collins delivered 353 of the incorrectly assembled actuators for installation on 737 Next Generation and 737 MAX variants. The parts do not pose an immediate safety risk, and a plan to remove them would be developed, Boeing added.
Homendy's letter reveals 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. "[Some] of these may [still] be spares, while others may currently be on airplanes in service," Homendy wrote. "Accordingly, it is essential that aftermarket installations of affected actuators also be clearly addressed."
Collins SVO-730 actuators are normally installed only on 737s equipped for Category III B low-visibility landing operations. In United's case, the actuators were in at least nine originally built for Category III B operations but later reconfigured for less-restrictive Category III A. United's 737s do not require Category III B capability.
The incident aircraft, N47280, was delivered in February 2023. The aircraft came "configured with a SVO-730 rudder rollout guidance servo that was disabled per UAL’s delivery requirements to reconfigure the autoflight system from CAT IIIB to CAT IIIA capability," the NTSB's preliminary report said.
The NTSB's recommendation letter said UAL "in general...was unaware that the rudder rollout guidance actuator was installed" on nine of its aircraft. The parts were removed using instructions in a May 2024 service bulletin, the board added.
"We are concerned of the possibility that other airlines are unaware of the presence of these actuators on their 737 airplanes," Homendy wrote. "Consequently, their flight crews may not know what to expect if the rollout guidance actuator fails at low altitude or during landing and rollout, as occurred in this incident. Not making operators fully aware of the installed systems and equipment on the airplanes delivered to them is unacceptable and cannot continue to be tolerated."
The actuators contain incorrectly assembled components that can cause moisture to seep in and freeze at altitude, leading to rudder jams. Tests by Collins, Boeing, and the NTSB show a significant amount of force on rudder pedals may be needed to break a jammed rudder free.
The NTSB is concerned that advising pilots to use such force could pose other risks, such as a "sudden, large, and undesired rudder deflection that could unintentionally cause loss of control or departure from a runway," its recommendation letter said. The board urged Boeing to review its pilot instructions and consider potentially safer alternatives.
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