Opposition has arisen to a regulatory exemption Boeing has requested for the 737 Max 7’s and Max 10’s stall-management yaw damper (SMYD), while Boeing continues insisting its proposal poses no safety threat and that the SMYD is well proven.
Boeing in January asked the Federal Aviation Administration for a temporary exemption that would allow the long-delayed Max 7 and 10 to be certificated despite Boeing not yet having demonstrated that the types’ SMYDs meet new, stricter software requirements.
If accepted, the exemption would also allow the company to more-quickly introduce in-development “enhanced angle-of-attack safety features” for all Max variants, including for the already in-service Max 8 and 9.
Boeing asked that the exemption be good through end-October 2028. Between now and then, it intends to complete work to demonstrate that the SMYD, unchanged, meets FAA requirements. Boeing badly needs to get its Max 7 and Max 10 certificated and into customers’ hands following years-long delays.
But the Air Line Pilots Association, International (ALPA) is pushing back, asking the FAA to reject Boeing’s request on safety grounds.
“ALPA believes the certification of the SMYD system should be concluded before entry into service,” the union told the FAA in a 3 February letter. “ALPA furthermore does not agree with the 3.5 years Boeing is asking for an exemption.”
The union warns the exemption would mean the software would be permitted to meet a reduced reliability threshold.
ALPA could not immediately be reached for further comment.
Boeing says the plan poses no safety concern considering the proven reliability of the system.
“The specific software for the 737-7 and 737-10 has undergone extensive testing and reviews, which confirmed there is no impact from any software adjustments on the airplane’s safety or reliability,” it says.
The exemption request applies to rules defining allowable failure probabilities for systems for which such failures could affect continued safe flight.
The manufacturer certificated previous SMYDs to “Level B”, as specified in guidance published by the Radio Technical Commission for Aeronautics, a standards-setting group. As such, Boeing’s in-service Max 8 and 9 were certificated to those standards.
However, “during 737-7 development and certification of the yaw damper function, updated analysis led Boeing and the FAA to determine that the SMYD should now be certified to Design Assurance Level A,” Boeing’s filing says. “Additional certification activity will be needed.”
“Granting this exemption will have no adverse impact on safety,” Boeing adds. “The 737NG and Max fleet has accumulated over 270 million flight hours in more than 25 years of service. In that time, the yaw damper system has established a performance and safety track record of high integrity and reliability,” Boeing says.
It has found “no reported operationally relevant issues related to yaw-damper malfunctions caused by the SMYD”.
Boeing describes the Max’s SMYD as “an electronics unit that provides stall warning, stall identification and yaw damper functions”.
In addition to ALPA, The Foundation for Aviation Safety – a nonprofit formed by Boeing whistleblower and former 737 production manager Ed Pierson – opposes the FAA granting Boeing’s request.
AOA ’ENHANCEMENT’
The exemption affects more than only the Max 7 and Max 10.
It also impacts the enhanced angle-of-attack (EAOA) system Boeing is developing for all Max models. Boeing first intends to roll out the update, which involves SMYD software changes, to the Max 10 before introducing it to other variants.
“Without the time-limited exemption, the EAOA safety features cannot be enabled, delaying critical safety enhancements until the SMYD is demonstrated to be compliant,” Boeing’s request says.
The company has been developing the update following scrutiny of the current system, which has only two AOA sensors. AOA failures were among factors contributing to two deadly Max 8 crashes, in 2018 and 2019, and Boeing committed to improving the system as part of European regulator EASA’s decision to lift the Max 8 and 9’s grounding in 2021.
The update involves adding a third “synthetic” AOA sensor to the Max, which will “enhance the system integrity and reduce the flight-crew workload in the event of air data and angle-of-attack failures”, Boeing says.
Boeing in 2023 had received a separate exemption for the SMYD on the 737 Max 7, though that exemption applied to lightning and radiation rules.
