Boeing still has to make “significant changes” to improve the quality and safety of its airplanes, according to the head of the Federal Aviation Administration.

After two crashes of Boeing 737 Max airplanes and a door plug that fell off of another, mid-flight, FAA Administrator Michael Whitaker testified before the House of Representatives about his agency’s oversight of Boeing.

Federal Aviation Administration officials and the House Transportation Committee debated how Boeing could improve safety.

Boeing must do more to improve the aircraft safety following a door plug blowout in January and other mishaps, Federal Aviation Administration Administrator Mike Whitaker told a House committee Tuesday.

Boeing Co. will need three to five years to rebuild its safety culture that regulators have found to be rife with shortcomings, the top US aviation safety official said.

The head of the Federal Aviation Administration will tell Congress on Tuesday the agency will hold Boeing accountable to ensure the planemaker is building safe airplanes and will revamp its own safety management program.

Boeing (BA) isn’t done doing what it needs to do in order to live up to the expectations of the Federal Aviation Administration in the wake of a January door plug blowout. Administrator Mike Whitaker said as much to Congress on Tuesday.

The Federal Aviation Administration is working to revamp its oversight process after a door plug detached mid-flight on a Boeing 737 Max jet earlier this year, the head of the US agency said on Tuesday.