SEATTLE - Boeing restarted production of its best-selling 737 MAX jetliner last week, about a month after the end of a seven-week strike by 33,000 factory workers, according to three sources familiar with the matter.

Getting the 737 MAX production line moving again is essential to the heavily debt-burdened planemaker's recovery, and Boeing has about 4,200 orders for the jetliner from airlines eager to meet growing global demand for air travel. 

Production resumed on Friday, said one of the sources, who all spoke on condition of anonymity because they were not authorized to speak with media. Boeing declined to comment.

The production restart had not been previously reported.

The head of the Federal Aviation Administration, Mike Whitaker, told Reuters on Thursday that Boeing had not yet resumed 737 MAX production but planned to do so later this month.

The company's plans to increase 737 MAX production to a targeted 56 airplanes a month have been stymied by a series of setbacks including two fatal crashes, the COVID-19 pandemic, supply chain problems, production safety concerns and increased regulatory scrutiny, along with the recent strike.

The FAA capped production at 38 737 MAX planes per month in January after a door panel missing four key bolts flew off an Alaska Airlines 737 MAX 9 during a flight that month, exposing serious safety issues at Boeing.

Whitaker last week declined to say when he thought the FAA would restore Boeing's ability to produce more than 38 planes per month, but said he would be surprised if it was less than multiple months before the company gets close to the 38 maximum.

Jefferies analysts expect Boeing will produce an average of 29 737 MAX planes per month in 2025, they said in a note to clients on Sunday.