(Adds more from senator and FAA and Boeing comment)

By David Shepardson

WASHINGTON, Jan 11 (Reuters) - The chair of the Senate Commerce Committee on Thursday asked the Federal Aviation Administration (FAA) for answers on its oversight of Boeing’s production systems after a cabin panel blowout on an Alaska Airlines 737 MAX 9 last week.

Senator Maria Cantwell said recent accidents and incidents "call into question Boeing's quality control."

It also appeared the FAA's oversight processes may not have been effective in ensuring Boeing produced airplanes in a condition for safe operations, she added, noting planemakers are given 50 days of advance notice before "quality system" audits.

"In effect, manufacturers must only get their house in order once an audit is announced," she said.

Cantwell first asked the FAA in January 2023 to initiate a new "special technical audit" of 11 areas related to Boeing’s production systems.

She noted the FAA in April said the audit she sought was not needed because it had put in place tools to complete audits of Boeing for the bulk of the information at regular intervals.

A growing number of lawmakers have raised questions about Boeing's quality control and the FAA's oversight of the planemaker as the National Transportation Safety Board (NTSB) investigates the incident.

The FAA, which said it would respond directly to Cantwell, on Thursday opened a formal investigation into the 737 MAX 9 to determine if Boeing failed to ensure completed products conformed to its approved design and were in a condition for safe operation under FAA rules.

Boeing CEO Dave Calhoun told CNBC on Wednesday that a "quality escape" was at issue in allowing the MAX 9 to fly that suffered a cabin panel blowout.

In response to Cantwell's letter, Boeing said it would cooperate "fully and transparently" with the FAA and the NTSB on their investigations.

The senator asked the FAA by Jan. 25 to provide documentation of agency safety audits of Boeing and fuselage supplier Spirit AeroSystems over the last two years and for FAA to answers questions regarding the agency's oversight of manufacturers' quality control processes.

Cantwell also raised concerns about Boeing's "Verification Optimization" program that she said several years ago "resulted in eliminating thousands of quality inspections on each airplane, relying instead on mechanics self-verifying that they performed their work properly."

She said that had resulted in the elimination of 900 quality inspector positions at Boeing.