MICHEL MARTIN, HOST:
We're going to take another look at what prompted federal authorities to ground certain Boeing 737 MAX 9 aircraft. An Alaska Airlines plane suffered a mid-flight blow out of part of its fuselage last week. It made an emergency landing in Oregon. The few passengers with minor injuries have all been medically cleared, and the head of the National Transportation Safety Board, Jennifer Homendy, says everybody was fortunate as the event could have been more tragic. She confirmed that no one was in the two adjacent seats. For more on this, we've called John Cox. He is a retired airline pilot and now a safety consultant. Good morning.
JOHN COX: Good morning.
MARTIN: So first, would you just help us understand exactly what is this door plug that seems to have given way?
COX: It is a plug that - in airplanes that airlines order with very large seating capacities can be turned into an emergency exit so that it depends on how the airline orders the airplane from Boeing, whether it's a plug, as it was in this case, or whether it's a usable emergency exit if the airplane has more than about 200 passengers in it.
MARTIN: Is this particular part a - considered to be or has it been considered to be a problem for the integrity of an aircraft in flight?
COX: No. This design has been in use for something over 15 years. There's another model of the 737 known as the 900ER and it also has this same sort of arrangement where it can be a plug or an emergency exit door. Some of the other MAX airplanes also have this. So this design has been in use for a number of years, and it's not proven to be problematic at all.
MARTIN: So this - so what I think I'm hearing you saying this wasn't a design flaw. So what happened?
COX: Well, that's the question the investigators are looking at. That plug is held in place by 12 what they call stops, and that's what the door actually rests up against or the plug rests up against. It's held in position by four bolts. And the investigators are going to look to see were those four bolts properly installed, was the proper hardware used, all of those things. And we're very fortunate they have found the plug itself. So they'll have both sides to be able to look at to see if there's marks from where the two pieces of metal moved against each other. And the metallurgist will be able to tell us a lot from that. So right now, we don't know. We know what happened, we don't know fully why. And then the follow up question, of course, is what do we need to do to prevent it from happening again? Right now, this still looks like it's a one-off. It's just something happened to this airplane.
MARTIN: Could you just say, though, a little bit more about how investigators are going to try to figure out, you know, what happened? 'Cause as you would imagine, in any situation like this, it's very frightening to people who fly.
COX: Oh, absolutely. And it's the fact that we don't have all the answers immediately that's also concerning to people. But as an aircraft investigator for something over 35 years, patience and doing it right, getting all the evidence gathered and then doing the analysis, that's critical to getting the best answers, and that's what matters.
MARTIN: OK.
COX: So they're going to look at where the plug fit in. Was it - did it - does it show the fact that it was scraped? Are all 12 of those stops there? Are the four bolts there? Are the nuts all there? Was there deformation or bending of the bolts or the holes? All of those things they're going to look at to try to understand the forces that resulted in this plug leaving the airplane.
MARTIN: OK. And how big of a problem is this for Boeing?
COX: I think Boeing has suffered a reputational damage. This is another case with dealing with the MAX. And I think this, so far, appears to be a one-off. But an operator around the world is going to look at this and say, OK, if we buy the MAX, are we buying a problem? So I think Boeing has some need to get ahead of this to the degree that they can.
MARTIN: That's John Cox. He's a retired airline pilot who is now a safety consultant. Mr. Cox, thanks so much for sharing this expertise with us.
COX: My pleasure. Transcript provided by NPR, Copyright NPR.
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