US lawmakers have asked the Federal Aviation Administration (FAA) to provide information about two potentially “catastrophic” safety concerns involving the 737 Max and 787 – issues unrelated to the Max’s grounding.

US lawmakers have asked the Federal Aviation Administration (FAA) to provide information about two potentially “catastrophic” safety concerns involving the 737 Max and 787 – issues unrelated to the Max’s grounding.

A 7 November letter to FAA administrator Stephen Dickson from the House Committee on Transportation and Infrastructure lays out the concerns, which involve rudder cable protection on the 737 Max and the 787’s lightning protection.

“Both appear to involve serious, potentially catastrophic safety concerns raised by FAA technical specialists that FAA management ultimately overruled after Boeing objected”, says the letter. “These incidents raise questions about how the agency weighs the validity of safety issues raised by its own experts compared to objections raised by the aircraft manufacturers.”

Signed by committee chair Peter DeFazio and aviation subcommittee chair Rick Larsen, the letter asks Dickson to explain why the agency approved both systems despite internal FAA opposition. DeFazio and Larsen are both Democrats.

The FAA declines to comment to FlightGlobal, saying, “We will respond directly to the chairman”.

Boeing says it “is aware of both issues raised in” the letter.

“We are confident that each was properly considered and addressed by Boeing, thoroughly reviewed with and approved by the FAA, and handled in full compliance with the processes governing review and disposition of such issues,” the company adds.

The letter questions the “adequacy” of the 737’s Max’s rudder cable protection, and whether the cable could by severed in the case of an uncontained engine failure.

The FAA’s Transport Airplane Directorate in 2014 sent a memo to the FAA’s Aircraft Certification Service saying the Max’s rudder cable had inadequate protection and noting Boeing had agreed to comply with 1997 guidance issued by the FAA in response to the deadly 1989 crash of a United Airlines aircraft near Sioux City, Iowa.

But, Boeing “objected to making changes to the design of the 737 Max rudder cable, arguing that changes would be impractical and noting the company’s concern about the potential impact on resources and programme schedules”, the House letter says.

The FAA in 2016 offered Boeing the ability to comply with regulations without design changes, though six FAA “specialists” refused to support that decision, the letter says.

An FAA safety review panel took up the matter. It concluded the FAA had insufficient information to determine if the 737 Max rudder protection complied with regulations. It also found that design changes were indeed a practical means of compliance, the letter says.

“Despite these concerns, the 737 Max gained certification from the FAA two months later, in March 2017,” the letter says.

It also calls attention to changes Boeing made to the 787’s lightning protection system. The company removed copper foil from part of the aircraft’s wing, which “could result in significantly higher conducted currents… as well as increase the number of ignition sources in the fuel tanks”, the letter says.

“Multiple FAA specialists” objected to that change, believing it failed to comply with regulations. Likewise, the FAA office that oversees Boeing rejected the change in February 2019.

Boeing appealed that rejection, and in March the FAA reversed its decision, greenlighting Boeing’s change, the letter says.

The rudder and lightning protection cases suggest that the opinions of FAA experts were “circumvented or sidelined” in favour of Boeing’s wishes, the letter says.

It asks the FAA’s Dickson to explain why the agency overruled its own specialists and to address concern that manufacturers might sidestep FAA specialists by appealing directly to senior FAA managers.

The lawmakers asked Dickson to respond by 21 November.

Story corrected on 8 November to note that congressmen Peter DeFazio and Rick Larsen, both Democrats, signed the letter. Committee ranking member Sam Graves, a Republican, did not signed the letter.