737 Mid-Cabin Emergency Exit Doors

This video is in response to the incident to Alaskan Airlines flight AS 1282 whose mid-cabin emergency exit door detached in-flight whilst climbing through 16,000ft on 5 Jan 2024. Fortunately, there were no injuries.

In it I cover the reason for the mid-cabin exit door, its construction and operation, Door Warnings & Flightlocks, the SPSEU, MAX PSEU Differences and Alaskan 1282.

*** Errata A deactivated mid-cabin exit door limits the maximum pax capacity to 189, not 175 as I stated in this video. ***

Contents:
0:42 Introduction
1:27 Operation
4:59 Options
14:31 Door Warnings & Flightlocks
17:22 SPSEU
19:36 MAX PSEU Differences
21:44 Alaskan 1282

[MentourPilot]

Very helpful! I do fly the B737-8200 so I know how to operate the doors but this gave a lot more context.

[blancolirio]

What a ridiculously complicated crew alerting system to comply with an antique Type Certificate. All this could have been incorporated into a modern EICAS system under a new design and Type Cert.
Thanks for all the details Chris!

[scott]

Not seen your channel before, but glad this video came up on my recommended list today. Really clear, excellently narrated, and informative video. subbed to your channel.

[USAmerican]

As an Aerospace Engineer, my "guess" is the lower hinge bolts were not installed properly. It looks like they are in an out of the way hard to see location. Could have been overlooked during a demanding work day.
So as the plane climbs to altitude air pressure pushes out on the door, and it bends the door outward slightly. The lower hinge sliders move up slightly due to this bending. All of the upwards loads are now being taken by the two upper bolts.
After a few dozen flights/cycles, those two overloaded upper bolts fail and allow the door to pop up and off.

[johnnywalker]

I'm a 737-9MAX Captain. Thank you so much for your video.

[leg]

Well done Chris Brady! Your videos immediately sprang to mind after this event occurred. Powerful education tool for all of us. Thank you !

[mnu]

Best technical channel Chris, perfect timing on this. Surprisingly this occurred not long after the loose rudder bolt finding that came out of an inspection as well on another operator.

[xrisc]

The sign of a great teacher is the ability to make anything understandable to anyone of average intelligence. I have average intelligence but little aviation knowledge yet this all clear to me and interesting! I watched your other vid about the door last night and today I saw so much more when it was on the news. I sounded so smart when I pointed out the hinges, stops, and bolts. Thank you!

[coriscotupi]

Not a true door, but rather a plug held on with 4 bolts? Another instance of missing or inadequately torqued nuts (or bolts)?
What an informative video, posted just hours after the incident. Well done, sir.

[sunflower-ooff]

Lucky whoever is flying with you...your voice is enough to calm anyone down..your knowledge is even better .👌💛

[rosscorr]

Wow, thanks for this brilliant overview and explanation of this door option. Only wish some in the media had viewed this before rushing to comment but hopefully your insightful video may correct some of the miss-reporting of this incident.

[cyber]

Thanks so much Chris for making this video about the plug situation. Everyone at Alaska Airlines is very concerned about this, so we’re looking for everything we can find out. I’m sure the NTSB will have something to say fairly soon I hope. But as always, your stuff is fantastic and I appreciate all the work you put in on behalf of those of us who fly the 737. Alaska grounded their entire fleet of Max aircraft until a special inspection could be done. I’m hearing through the grapevine that about 1/4 of those planes have been inspected in the last day. But until they’re all done the entire fleet of 65 max airplane stays on the ground.

[peterlee]

Great to see a video that covers the subject so fully - and produced in such a short time after the Alaskan incident. It is sobering to think how the occupants of the plane "dodged the bullet"! If those seats next to the door had been occupied, I would guess people would have been sucked out. And how lucky they were that they were only at 16000 feet. And also lucky that the departing door plug did not hit the tail surfaces ... It will be interesting to see the results of the investigations.

[john]

There are reports that this aircraft has had a number of pressurisation warnings in the last week. It could be that the retaining bolts have come lose over this time. Of course, the door warning lights being disabled would not have helped.

[alasdairhompstead]

A very helpful piece. I thought it was a variation of the type of door fitted to the D3 position on the 757. This appears to be the case, and it makes sense that it would use the same latching points as the operable emergency exit along with bolts to lock it out and keep it clamped closed. The Alaskan aircraft was in maintenance on Jan 1st. Possibly coincidence.

[GregInTokyo]

After watching so many channels and the regular news media dumb-down the causes of these incidents, it's great to find a channel that goes into serious technical depth. Very refreshing, although I can see where all the acronyms might scare some people off.

[tarkwright]

Chris, You got this video out fast. I’m impressed.
Thanks!

[allaboutaviation]

Wow, amazing insides into the door/plug design

[philipcollura]

Have viewed most of your videos, have your book too.

The only thing I can't comprehend is how you produced such a detailed and illustrated video so quickly. I'd hope Boeing and the NTSB contacts you for opinions / input .

[HowShouldIKnow]

Brilliantly done.
Technically precise, substantiated and well delivered!