Passengers heard a 'whistling sound' on a previous flight on the same Boeing 737 that lost its door plug, lawsuit says

• A lawsuit says a "whistling sound" previously came from the door plug of the Alaska Airlines blowout jet.
• "This plane was a ticking bomb," the attorney, who is representing passengers on the flight, said.

A "whistling sound" came from the door plug on a previous Alaska Airlines flight on the same jet involved in last month's blowout, a lawsuit says.

"This plane was a ticking bomb," said Mark Lindquist, an attorney representing 22 passengers who were on board Alaska Airlines Flight 1282.

The new detail was added to the lawsuit as part of an amended complaint filed Wednesday, according to a press release from Lindquist.

The Boeing 737 Max 9 jet lost its door plug, which covers a deactivated emergency exit, in midair on January 5. Oxygen masks were deployed, although nobody was seriously injured as the plane returned to Portland International Airport 20 minutes after takeoff.

In its preliminary report released Tuesday, the National Transportation Safety Board said the plane left Boeing's factory missing key bolts designed to secure the door plug.

Alaska Airlines CEO Ben Minicucci previously told NBC, "We had a guardian angel," because the 178-capacity plane had seven unoccupied seats — which luckily included those next to the gaping hole.

The amended complaint says passengers on a previous flight on the same plane heard "a whistling sound coming from the vicinity of the door plug."

Passengers then notified flight attendants who informed the pilots, it adds according to Lindquist's press release.

It alleges that no known further action was taken, "after the pilot checked cockpit instruments, which purportedly read normal."

The 737 Max 9 jet had been restricted from flying long distances over water due to three previous pressurization warnings in December and January. Lindquist did not specify the date when passengers heard the whistling sound.

Timothy Loranger, an aviation lawyer and former aircraft mechanic, told the Associated Press: "We know that the bolts were missing. So this sound makes sense."

"If they heard that whistling noise, that's very possible to have been an indication that the aircraft had some small leaks around the seal and that it wasn't keeping pressure properly," he added.

Boeing and Alaska Airlines did not immediately respond to a request for comment from Business Insider, sent outside US working hours.