The top U.S. aviation regulator said Thursday that the Federal Aviation Administration should have been more aware of manufacturing problems inside Boeing before a panel blew off a 737 Max during an Alaska Airlines flight in January.

"FAA's approach was too hands-off — too focused on paperwork audits and not focused enough on inspections," FAA Administrator Mike Whitaker told a Senate committee.

Whitaker said that since the Jan. 5 blowout on the Alaska jetliner, the FAA has changed to "more active, comprehensive oversight" of Boeing. That includes, as he has said before, putting more inspectors in factories at Boeing and its chief supplier on the Max, Spirit AeroSystems.

Whitaker made the comments while his agency, the Justice Department and the National Transportation Safety Board continue investigations into the giant aircraft manufacturer. The FAA has limited Boeing's production of 737 Max jets to 38 per month, but the company is building far fewer than that while it tries to fix quality-control problems.

Investigators say the door plug that blew out of the Alaska jet was missing four bolts that helped secure it in place. The plug was removed and reinstalled at a Boeing factory, and the company told federal officials it had no records of who performed the work and forgot to replace the bolts.

"If Boeing is saying, 'We don't have the documentation, we don't know who removed it,' where was the (FAA) aviation safety inspector?" Commerce Committee Chair Maria Cantwell, D-Wash., asked Whitaker.

"We would not have had them on the ground at that point," he said.

"And why not?" Cantwell responded.

"Because at that point the agency was focusing on auditing the internal quality programs at Boeing," Whitaker said. "We clearly did not have enough folks on the ground to see what was going on at that factory."

Whitaker said the FAA is hiring more air traffic controllers and safety inspectors but is competing with the aerospace industry for talent. He said the FAA has lost valuable experience in the ranks of its inspectors with its current, younger workforce.