off an Alaska Airlines flight has been recovered.

A teacher near Portland Oregon found# the so-called door plug in his an d authorities hope it will help them figure# out what went wrong.

The accident that happened## 16,000 feet in the air has sparked new# concerns about aircraft maker Boeing.

Our aviation correspondent,# Miles O'Brien, has the latest.

MILES O'BRIEN: Investigators from the National# Transportation Safety Board were in Portland to## try to determine what caused the fuselage# blowout on the Alaska Airlines jetliner.

It's the latest in a string of setbacks# to plague Boeing's 737 MAX aircraft.## Friday's incident affected a# plug covering an unused exit## door.

Passenger video showed the gaping# hole in the side of the plane.

The rapid## decompression caused the cockpit door# to fly open.

Headrests ripped off seats.

The two seats next to the panel# that blew out were unoccupied.## None of the 171 passengers or six# crew members were seriously hurt.

Emma Vu was one of those passengers.

EMMA VU, Alaska Airlines Passenger: I just feel# tu rbulence, just because the masks came down# too.

So, that's wh this is something way different.# And yes, I started freaking out.

MILES O'BRIEN: The Alaska Airlines flight took# off from Portland shortly after 5:00 p.m. Friday## en route to Ontario, California.

The panel# blew off about six minutes into the flight,## as the plane was at an altitude of 16,000 feet.

The plane returned to Portland,## making an emergency landing about# 13 Jennifer Homendy chairs the National# Transportation Safety Board.

JENNIFER HOMENDY, Chair, National Transportation# Safety Board: So, it was described as chaos,# very loud, between the air and everything# going on around them.

And it was violent when the rapid decompression in# the door was expelled out of the plane.

MILES O'BRIEN: The Federal Aviation Administration# quickly grounded Boeing 737 MAX 9 jets with the## same panel to undergo safety checks, forcing# the cancellation of hundreds of flights.

The NTSB said the jetliner that suffered# the blowout was not being used for flights## to Hawaii after a warning light that could# have indicated a pressurization issue lit## up on three separate flights.

They acknowledged# the light may be unrelated to Friday's incident.

All this comes after problems with# the 737 MAX's MCAS safety system led## to deadly crashes of the planes# in Indonesia and Ethiopia back in## 2018 and 2019.

That issue grounded# the MAX jets for nearly two years.

The airlines that fly the 737 MAX 9 are now# actively inspecting those plug doors to see## what might have gone wrong.

The Associated# Press, Geoff, is reporting that United has## found some loose bolts already, so we# will be watching that one very closely.

GEOFF BENNETT: More to come on that front.

So, Miles, we know previous flights made by the specific aircraft# involved in that incident.

There's no known## connection between that problem and the issue# with the midair blowout, at least not yet.

How is this investigation unfolding?

MILES O'BRIEN: Well, that's# something that we will be An d it could be completely coincident Imagine a scenario where there was some# sort of slow leak, which might have given## that indication of a pressurization problem# in the flight deck.

What's interesting is,## those lights came on in some cases while# the aircraft was taxing on the ground.

And so I don't know how much credence to put into## that right now.

Let's pin that# up on the bulletin board for now.

GEOFF BENNETT: Meantime, the NTSB released these## images of the recovered door pl plug does and why some models of this# aircraft have them and others don't.

MILES O'BRIEN: Well, the 737 MAX 9# is a little bigger than the MAX 8,## the one we talked about so# much over the recent years.

It can have upwards of 230 seats# in it.

Some low-cost airliners do,## in fact, cram that many seats in.# But if you have 189 seats or less,## you don't need those exit doors, because# you don't have to get as many people out## in 90 seconds' time.

So they plug them.# And that's what happened in this case.

Air## Alaska was capped off at 189 people, and# so those doors were capped off as well.

GEOFF BENNETT: There's another curious, or# you could call it troubling, detail here,## in that the NTSB said that there was# no data available on the cockpit voice# recorder because it was not# retrieved within two hours.

And that's the point at which recording restarts# and overwrites the previous ho w could that even happen?

And what could it## have offered investigators if they# were able to hea MILES O'BRIEN: Yes, the airline industry# should be a little embarrassed about## all of this.

That two-hour loop really# kind of dates back to the days when they could only store so much# on these cockpit voice recorders.

Obviously, we're in an era where you have# unlimited virtually capability to record## that information.

In order to stop it from# recording, you have to pull a circuit breaker,## and nobody bothered to do that.# And so it got recorded back over.

It's high time -- the National Transportation# Safety Board has been asking this -- for this for years -- that the amount of time# that is on that loop, the amount that## is captured exceed 24 hours, actually 25 hours.# And the airlines have been slow to adopt this.

GEOFF BENNETT: We know this incident# happened at an elevation of 16,000 feet,## roughly three miles above Oregon.

How much of a# factor did that have in everybody' would things have been different had# this occurred at a higher elevation?

MILES O'BRIEN: Absolutely, Geoff.

The pressure differential is about two pounds per square inch.# It's much greater at 36,000 feet.

The## amount of pressure on the door up# there would be in excess of 50,000## pounds.

So it would have had much more of# an explosive event.

And, at that alt the time of so-called useful consciousness# for the passengers would be only 10 seconds.

So it would have been a much more dramatic,## possibly a situation where things didn't# come out as crew.

So a silver lining here that had# happened at a relatively low altitude.

GEOFF BENNETT: This is another black eye# for Boeing, which has seen a string of## incidents that have resulted in tragedies,# groundings, major co How are they responding to this?

MILES O'BRIEN: Well, they have issued just a# is a top priority and they're cooperating# with all the investigating authorities.

The company has announced a town hall to# presumably discuss some of these issues, but## there is a long string of issues here, which may# on the surface say -- they seem like they're not## connected, but you have to look at the big picture# and wonder why this happens repeatedly.

So, there## are clearly some questions about its# commitment to detail and safety at this point.

GEOFF BENNETT: Alaska and United Airlines, which# have a number of these Boeing models in their## fleet, they canceled more than 300 flights# today because of the 737 MAX 9 grounding.

How long might it take before these airlines are## back with these planes in the# air?

Or should they even be?

MILES O'BRIEN: Well, the inspections,# I think, are fairly straightforward.

We have already heard a little bit# about what United is finding.

in fact, it's a case of several bolts# that weren't tightened properly,## that should be a fairly easy thing to rectify# and put these planes back in the air.

I don't## think there's any fundamental design flaw# here.

If the bolts weren't tightened,## and they can be tightened properly, I think we# are all safe getting on board these aircraft.

GEOFF BENNETT: Aviation# correspondent Miles O'Brien.

Miles, thanks, as always.

MILES O'BRIEN: You're welcome, Ge