WASHINGTON A US Senate panel investigating Boeing's safety culture on Wednesday faulted the planemaker's quality practices and oversight by the Federal Aviation Administration citing documents obtained in an ongoing investigation.

The Senate Permanent Subcommittee on Investigations, which is holding a hearing Wednesday with FAA administrator Mike Whitaker, said Boeing workers continue to feel pressure to prioritise speed of production over quality.

The committee's Democratic staff said in a memo Boeing struggles to ensure employees are adequately trained, fails to ensure improper parts are not installed and its quality inspection procedures and the FAA’s review raises questions about qualifications and the independence of individuals performing inspections.

In some facilities, Boeing personnel are allowed to inspect their own work.

"Given the depth and history of Boeing’s safety deficiencies, its lack of candor with the FAA, and the agency’s reactive regulatory posture, the newly released information raises questions about the effectiveness of the FAA’s oversight of the company," the committee said.

Boeing said it has "taken important steps to foster a safety culture that empowers and encourages all employees to share their voice, but it will require continuous focus."

The FAA did not comment but Whitaker said at a House hearing Tuesday that Boeing needed to undertake significant safety culture improvements that might not be completed for years.

The committee disclosed details of an FAA audit completed after a door plug missing key bolts blew off a new Alaska Airlines 737 MAX 9 jet at 16,000 feet in January.

The Justice Department and FAA are investigating.

The 116-page FAA letter details 97 Boeing allegations of non-compliance that span "issues in Boeing’s manufacturing process control, parts handling and storage, and product control." The audit found 23 examples where employees "failed to follow processes or lacked proficiency," the memo said.

Whitaker has barred Boeing from expanding MAX production until it makes major quality improvements.

The committee said an internal Boeing survey from May shows many machinists feel pressured to prioritise speed over quality during airplane production and said the FAA identified quality inspection deficiencies at Boeing in 2017.

Whitaker's written testimony for the Senate hearing says the FAA will "expeditiously provide notice, in real time, of any activities that may be criminal so that DOJ can take any action they deem appropriate."

Boeing agreed to plead guilty to a criminal fraud conspiracy charge in July after breaching a 2021 agreement with DOJ.

  - Reuters