A group of U.S. lawmakers want the Federal Aviation Administration to answer key questions about its oversight of Boeing in the wake of a 737 MAX 9 mid-air emergency, including whether it found serious quality issues at the planemaker.

In the letter sent on Wednesday, the legislators also asked whether the FAA was contemplating changes to the way it oversaw the manufacturing processes of Boeing and its suppliers. Reuters was the first to reveal the letter.

The FAA, acting after a mid-air cabin panel blowout on a new Alaska Airlines MAX 9, says it will audit all elements of production at Boeing and fuselage production at Spirit AeroSystems.

In the letter, the legislators asked FAA Administrator Mike Whitaker to answer whether — before or after the accident — the agency found “any evidence of persistent quality control lapses in any of Boeing’s production lines.”

It was signed by House Transportation and Infrastructure Committee chair Sam Graves and Rick Larsen, the top Democrat on the committee, along with Representative Garret Graves, the chair of the aviation subcommittee and Democrat Steve Cohen.

Whitaker is set to testify Tuesday before the aviation subcommittee. An FAA spokesperson said the agency would respond to the letter.

“Is the FAA considering any changes to its broader on-site surveillance of Boeing’s and its suppliers’ manufacturing processes to help ensure its products conform to their type design?” the letter said.

“What changes, if any, is the FAA considering to its current risk model for inspecting production facilities?”

The FAA has scrutinized Boeing’s quality and other issues in recent years as it faced harsh criticism for its actions in the run-up to the MAX certification. Following two fatal crashes in 2018 and 2019, the FAA grounded the plane for 20 months and mandated significant software and training improvements.

The FAA says a team of two dozen aviation safety inspectors will conduct the new audit at the Boeing 737 facility in Renton, Washington, and at Spirit in Wichita, Kansas. The audit will also examine how Boeing transfers unfinished work from suppliers to its production lines.

The letter also asked whether the FAA was considering further action on Safety Management Systems (SMS) requirements “for aircraft part suppliers or other entities involved in aircraft manufacturing not captured by current regulations.”

The SMS are a set of policies and procedures to proactively identify and address potential operational hazards early on.

In March last year, the FAA told Congress it was ramping up oversight of Boeing following two fatal 737 MAX crashes in 2018 and 2019.

The FAA grounded 171 MAX 9 jets on Jan. 6, resulting in thousands of flight cancellations by Alaska Airlines and United Airlines. The grounding was lifted on Jan. 24.

The letter also asked whether airlines were able to receive the information they needed to ensure they could plan ahead and minimize potential operating disruptions.

(Reporting by David Shepardson, editing by David Ljunggren and Nick Zieminski)