United and Alaska Airlines will start flying the stricken Boeing 737 Max 9 again within days

• Alaska Airlines said it will return its first few 737 Max 9 jets to service on Friday.
• United will also bring the Boeing plane back to service from Sunday.

The Boeing 737 Max 9 will return to the skies on Friday, three weeks after the Alaska Airlines blowout, the carrier announced Wednesday.

According to Reuters, United Airlines — the biggest operator of the Max 9 with 79 of them — said it will start flying the jet again from Sunday.

It comes shortly after the Federal Aviation Administration announced that the jets had been cleared to resume flying following inspections.

On Alaska's Flight 1282 earlier this month, the door plug — which covers a deactivated emergency exit — came off in midair causing an uncontrolled decompression.

Nobody was seriously injured as the plane returned to Portland International Airport 20 minutes after takeoff, but the incident has opened Boeing to criticism. The Max 9 jet was delivered to the airline just 66 days earlier.

As inspections began following the FAA's Emergency Airworthiness Directive, the airlines found loose bolts on other planes too. The National Transportation Safety Board is investigating whether four bolts missing from the Flight 1282 door plug were ever installed.

Both Alaska and United's bosses slammed the American manufacturer on Tuesday.

"It makes me angry," Alaska Airlines CEO Ben Minicucci told NBC. "Flight 1282 should never have happened."

And United's Scott Kirby told CNBC he was "disappointed" and could change the order book following delays in the certification of the 737 Max 10.

Not all the Max 9 jets will immediately return to service because some haven't been through the full inspection process yet. Alaska Airlines expects all its inspections to be completed over the next week.

And for Boeing, there are still several issues ahead. FAA Administrator Mike Whitaker said, "Let me be clear: This won't be back to business as usual for Boeing."

The FAA said it will deny expansion of 737 Max production, which it is also investigating.

In a Wednesday statement, Boeing said: "We will continue to cooperate fully and transparently with the FAA and follow their direction as we take action to strengthen safety and quality at Boeing. We will also work closely with our airline customers as they complete the required inspection procedures to safely return their 737-9 airplanes to service."