The head of the US aviation regulator said it is increasing its oversight of Boeing and reviewing its practice of delegating some safety tasks to the beleaguered airline.
It followed an early January mid-flight blowout where a door plug blew off a Boeing 737 MAX 9 Alaska Airlines aircraft.
The Federal Aviation Authority (FAA), which on Tuesday appeared before US politicians of the Committee on Transportation and Infrastructure, subsequently grounded all 171 of the MAX 9 jets and placed an unprecedented ban on raising production volumes within the entire 737 MAX fleet of aircraft.
Some inspectors are to be kept on at Boeing and airplane part maker Spirit AeroSystems after a six-week production audit, the FAA head, Mike Whitaker, told the committee hearing.
The FAA administrator said the agency was “aggressively expanding oversight of new aircraft with increased floor presence at all Boeing facilities… We will follow the data and take appropriate and necessary action.”
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More inspectors are going to be needed as a result, Mr Whitaker added, as the regulator is sending 20 inspectors to Boeing’s 737 facility in Washington and six to a Spirit factory in Kansas.
Also under review, by an outside firm, is the long-standing FAA practice of delegating some critical safety tasks to Boeing, he said.
Thousands of flights were cancelled by users of the Boeing 737 MAX 9, Alaska Airlines and United Airlines, as a result of the grounding order, which was lifted on 24 January.
The FAA said 94% of the jets have returned to service.
No Boeing representatives were scheduled to testify at the Committee on Transportation and Infrastructure.
A separate regulator, the US National Transportation Safety Board (NTSB) is expected to publish a preliminary report of its investigation into the door blowout on Tuesday evening.