U.S. aviation investigators were in Portland, Oregon on January 7 trying to establish what caused a door panel to blow out of a brand-new Boeing passenger jet just minutes after takeoff, forcing pilots to make an emergency landing.

The Guardian reports the Boeing 737 Max 9 aircraft on January 5, with 171 passengers and six crew on board, lost an exit door, leaving a hole “the size of a refrigerator” in the side of the plane.

The weeks-old plane had been modified, requiring fewer emergency exits because it had fewer seats.

BBC News reported January 8 that the National Transportation Safety Board (NTSB) said the missing section of plane had now been found, in the back garden of a Portland teacher, and that investigators’ findings so far did not suggest a widespread flaw with the Boeing Max 9 aircraft. Speaking at a news conference January 7, Jennifer Homendy of the NTSB said pilots reported pressurization warning lights on three previous flights made by the specific Alaska Airlines Max 9 involved in the incident.

On January 7, thousands of passengers, mostly in the U.S., faced flight cancellations that are expected to continue into next week as airlines called in inspectors to comply with a Federal Aviation Administration (FAA) order.

Although no one was seriously injured during January 5’s emergency landing, the close call has raised fresh safety concerns about Boeing planes, which took place five years after two fatal accidents left 346 people dead and the U.S. company’s reputation in tatters.