VIDEO: Boeing 737 Max 9 aircraft under scrutiny after mid-air flight blowout

FLIGHT ANNOUNCEMENT:  We need everyone to remain seated with their seatbelts on right now.

EMILY BAKER, REPORTER:  A terrifying moment for the 177 people on board Alaska Airlines flight 1282.

FLIGHT ANNOUNCEMENT:  We are an emergency. We are depressurised. We do need to return back to you. We have 177 passengers.

EMILY BAKER:  Not long after take-off, part of the plane’s fuselage blew out – leaving a gaping hole in the aircraft 16,000 feet in the air.

PASSENGER:  There's a hole in the side of the plane! What the (bleeped) is that!

EMILY BAKER:  The plane made an emergency landing in the US city of Portland just 20 minutes after take-off.

Some passengers reported minor injuries, but authorities warn the January 5 incident could’ve been much worse.

JENNIFER HOMENDY, NATIONAL TRANSPORTATION SAFETY BOARD:  Think about what happens when you’re in cruise. Everybody’s up and walking, folks don’t have seatbelts on. We could’ve ended up with something so much more tragic.

EMILY BAKER:  What popped out was a door plug, which covered a potential additional exit.

Investigations into how it blew out of the Boeing 737 Max 9 are ongoing.

CLINT CROOKSHANKS, NATIONAL TRANSPORTATION SAFETY BOARD:  We have not yet recovered the four bolts that restrain it from its vertical movement, and we have not yet determined if they existed there.

EMILY BAKER:  Like millions of people around the world, Portland’s Bob Sauer watched news of the event with interest.

BOB SAUER:  It hadn’t dawned on me that it was actually in my neighbourhood was where the debris had come down.

EMILY BAKER:  He scoured his property for the missing door plug at a friend’s urging.

BOB SAUER:  I noticed that against the back of the property under a line of cedar trees I’d planted, there was something gleaming and white that should not have been there, oh my goodness.

And as I started walking towards it my heart started beating faster because it looked very much like an airplane part – and it was.

EMILY BAKER:  He reported the find to the National Transportation Safety Board, who collected the debris earlier today.

The discovery has made the science teacher popular with his pupils.

BOB SAUER:  My students today were all very excited about it and I didn't really get any schoolwork done at school today, because so many people came in to talk to me about it.

EMILY BAKER:  US authorities and several airlines in other countries have grounded Max 9s pending further inspections.

America’s United Airlines has announced it had found loose bolts in door plugs on its planes of the same make.

No airlines fly Max 9s into Australia.

DR SONYA BROWN, UNSW SENIOR LECTURER:  At this stage I don't really see any impact on Australian aviation because we don't really have any of these aircraft with these plugs flying in Australia.

Both Virgin and Bonza have either Max 8 or Max 8s on order. But the Max 8, the base Max 8 model, do not include this extra optional exit, hence the plug.

EMILY BAKER:  The Boeing 737 Max series has come under scrutiny in recent years.

In 2018, a Lion Air flight crashed into the Java Sea just 10 minutes after take-off killing 189 passengers and crew.

Less than five months later, an Ethiopian Airlines flight also nosedived - 157 people were killed.

SONYA BROWN:  That was related to an issue with a flight control system, which was intended to prevent stall.

The whole series of aircraft was grounded for almost two years, and Boeing has put in place software fixes that would have, if they were in place at the time, prevented both of those incidents.

EMILY BAKER:  Ed Pierson worked as a manager on the 737 Max program between 2015 and '18

He’s long voiced his concern that schedules trump safety at the US manufacturer.

ED PIERSON, FMR BOEING EMPLOYEE:  This is just the tip of the iceberg.

There's, you know, constant pressure, they're having issues with parts, not enough skilled labour, I mean, all the variables that were in place before the two Max crashes are still there.

EMILY BAKER:  He says without drastic change, he’ll avoid flying on the planes he once helped build.

ED PIERSON:  I would not fly a Max, I absolutely would not recommend flying a Max. And I don't mean just the dash nines that are having these problems today, because a lot of the reports and stuff we're seeing is also in the other model Max and so that plane needs to be grounded, period, and it needs a lot of work to get it back in the air. And I don't even know if it's possible to fix that plane permanently.

EMILY BAKER:  Boeing declined to answer specific questions, instead saying “safety is our top priority and we deeply regret the impact this event has had ... we will remain in close contact with our regulator and customers.”

The investigation into flight 1282 could take up to a year – aviation experts like Dr Sonya Brown stress air travel is safe.

SONYA BROWN:  All aircraft are certified to high standards. Sometimes incidents happen just like, if you jump in a car, sometimes you could be involved in a car accident.

There's some level of risk with everything we do but overall aviation is the safest form of transport we have.