US Federal officials on Saturday ordered the immediate grounding of some Boeing 737 Max 9 jetliners until they are inspected after an Alaska Airlines plane suffered a blowout that left a gaping hole in the side of the fuselage, according to AP.

The required inspections take around four to eight hours per aircraft and affect about 171 airplanes worldwide.

Alaska Airlines said in a statement that of the 65 737 Max 9 aircraft in its fleet, crews had inspected the paneled-over exits as part of recent maintenance work on 18 planes, and those were cleared to return to service Saturday. Inspections for the remaining aircraft were expected to be completed in the coming days, the company said.

An Alaska Airlines jetliner blew out a portion of its fuselage shortly after takeoff 3 miles (4.8 kilometers) above Oregon late Friday, forcing the pilots to make an emergency landing as its 171 passengers and six crew members donned oxygen masks.

No one was seriously hurt as the depressurized plane returned safely to Portland International Airport about 20 minutes after departure.

Authorities are still looking for the door from the paneled-over exit and have a good idea of where it landed, near Oregon Route 217 and Barnes Road in the Cedar Hills area west of Portland, National Transportation Safety Board Chair Jennifer Homendy said at a news conference late Saturday.

“If you find that, please, please contact local law enforcement,” she said.

It was extremely lucky that the airplane had not yet reached cruising altitude, when passengers and flight attendants might be walking around the cabin, Homendy said.

“No one was seated in 26A and B where that door plug is, the aircraft was around 16,000 feet and only 10 minutes out from the airport when the door blew,” she said.