Alaska Airlines 737-900 MAX loses a door in-flight out of PDX
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I'm the auditor - I'm here to help you
The trouble with such "oversight", auditing, or regulatory organisations is they quite soon find the easiest way to perform their role is to ask the business they are meant to be checking to do their work for them. There are numerous examples of this, not least "Delegated Authority" at Boeing.
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Airflow over the door plug
If the bottom front bolt alone was missing, could the air flow over the door plug have pulled the corner out sufficient to shear off the door plug from the frame?
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Stop bolts
Thinking further about the way the upper and lower stop bolts work. The lower stop bolts will be much stronger than the upper ones because of the way they are fitted. The upper bolts attached to the guide at their ends. The guide roller then contacts the bolt at its mid point which is its weakest point, being furthest from where it is attached to the guide. The lower bolts again attach at their ends to the green hinge bracket. The force on those is applied by the shaft which should be applied along the length of the bolt and under extreme stress would be split between each end of the bolt at its strongest point.
Assuming this is correct, would it be fair to say that the lower bolts are the important ones and the upper ones are just a secondary insurance? Now if the lower bolts were missing the upper bolts would have to do all the work. There must be some play in the fitting of the upper bolts such that the guide roller can move a little bit between the top of the guide and the bolt. Without that it would be very hard to insert the lock bolt.
If the lower bolts are missing the plug door would be able to bounce between the top of the guide and the lock bolts with any aircraft movement. Eventually would that be enough to cause the two bolts to fail? If they did fail then that could also damage the guide near the fixing holes for the bolt.
This would explain why the failure took some time to happen. From what everyone else has said, it is hard to see how the plug would have popped out after a few months if no bolts were present. Unless they were loose of course.
Assuming this is correct, would it be fair to say that the lower bolts are the important ones and the upper ones are just a secondary insurance? Now if the lower bolts were missing the upper bolts would have to do all the work. There must be some play in the fitting of the upper bolts such that the guide roller can move a little bit between the top of the guide and the bolt. Without that it would be very hard to insert the lock bolt.
If the lower bolts are missing the plug door would be able to bounce between the top of the guide and the lock bolts with any aircraft movement. Eventually would that be enough to cause the two bolts to fail? If they did fail then that could also damage the guide near the fixing holes for the bolt.
This would explain why the failure took some time to happen. From what everyone else has said, it is hard to see how the plug would have popped out after a few months if no bolts were present. Unless they were loose of course.
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Hinges
Look at the hinge from the plug. Its shaped like a question mark. The end that is "C" shaped attaches to the floor of the plane. The other end has the spring and passes through the fitting in the door. Without the door attached, the plug hinge it is only capable of folding down about 90 degrees before it hits the lower part of the door frame. The only photos Ive seen of that hinge in that position are post incident photos from the incident plane.
Look at the video I posted earlier of the emergency exit in motion. It folds down about 140 degrees. The plug hinge does not have that range of motion.
In my opinion, its pretty obvious that the hinges are different between the plug and the door. And I can tell that from the exit door photo above and any of the dozens of mid exit plug photos like the one in post 843. In fact, stop pin fittings, guide fittings and the perimeter frame they attach to seem to be about the extent of common parts between the plugs and exit doors.
Does that prove they they use different springs. Nope. But it does prove that it cant be assumed that are even springs involved in the exit door hinges. And I haven't seen any photographs that prove the exit doors have similar hinges to the plugs.
Why are the guide fittings identical? Perhaps they didn't see a need to have different parts that serve the same purpose, that is guiding the door up on a bearing in the frame. Perhaps they didn't see a risk that someone would try to bolt an exit shut. Perhaps they do bolt the inactivated emergency exits shut. Reuse of one part doesn't mean they reused as many as possible. Weight and maintenance are much larger issues than maximizing parts commonality.
Look at the video I posted earlier of the emergency exit in motion. It folds down about 140 degrees. The plug hinge does not have that range of motion.
In my opinion, its pretty obvious that the hinges are different between the plug and the door. And I can tell that from the exit door photo above and any of the dozens of mid exit plug photos like the one in post 843. In fact, stop pin fittings, guide fittings and the perimeter frame they attach to seem to be about the extent of common parts between the plugs and exit doors.
Does that prove they they use different springs. Nope. But it does prove that it cant be assumed that are even springs involved in the exit door hinges. And I haven't seen any photographs that prove the exit doors have similar hinges to the plugs.
Why are the guide fittings identical? Perhaps they didn't see a need to have different parts that serve the same purpose, that is guiding the door up on a bearing in the frame. Perhaps they didn't see a risk that someone would try to bolt an exit shut. Perhaps they do bolt the inactivated emergency exits shut. Reuse of one part doesn't mean they reused as many as possible. Weight and maintenance are much larger issues than maximizing parts commonality.
I also subscribe to the view expressed earlier that closing the door plug from the assisted lift position would be likely to be achieved by pulling down with one hand near the top of the door and pressing down with a boot on the bottom of the door leaving the other hand free to insert a temporary sprag of some sort probably in one of the guide tracks.
Every indication is a locking nut plate was used.
Just look at the recovers plug photos showing parts of 2 bolts still present, held by the nut plates.
Some more from the Seattle Times, including this about Sen Maria Cantwell. Cantwell had asked to see the last 24 months of notices of FAA quality systems audits related to Boeing and one of its suppliers, Spirit AeroSystems.
Spirit, based in Wichita, Kan., builds the entirety of the fuselage for the 737 MAX 9, before sending it to Boeing’s Renton plant by train.
“Recent accidents and incidents … call into question Boeing’s quality control,” Cantwell wrote in the letter to the FAA Thursday. But, she continued, “it appears that the FAA’s oversight processes have not been effective” in ensuring Boeing’s planes are safe.
https://www.seattletimes.com/busines...so-is-the-faa/
Spirit, based in Wichita, Kan., builds the entirety of the fuselage for the 737 MAX 9, before sending it to Boeing’s Renton plant by train.
“Recent accidents and incidents … call into question Boeing’s quality control,” Cantwell wrote in the letter to the FAA Thursday. But, she continued, “it appears that the FAA’s oversight processes have not been effective” in ensuring Boeing’s planes are safe.
https://www.seattletimes.com/busines...so-is-the-faa/
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Look at the hinge from the plug. Its shaped like a question mark. The end that is "C" shaped attaches to the floor of the plane. The other end has the spring and passes through the fitting in the door. Without the door attached, the plug hinge it is only capable of folding down about 90 degrees before it hits the lower part of the door frame. The only photos Ive seen of that hinge in that position are post incident photos from the incident plane.
Look at the video I posted earlier of the emergency exit in motion. It folds down about 140 degrees. The plug hinge does not have that range of motion.
In my opinion, its pretty obvious that the hinges are different between the plug and the door. And I can tell that from the exit door photo above and any of the dozens of mid exit plug photos like the one in post 843. In fact, stop pin fittings, guide fittings and the perimeter frame they attach to seem to be about the extent of common parts between the plugs and exit doors.
Does that prove they they use different springs. Nope. But it does prove that it cant be assumed that are even springs involved in the exit door hinges. And I haven't seen any photographs that prove the exit doors have similar hinges to the plugs.
Why are the guide fittings identical? Perhaps they didn't see a need to have different parts that serve the same purpose, that is guiding the door up on a bearing in the frame. Perhaps they didn't see a risk that someone would try to bolt an exit shut. Perhaps they do bolt the inactivated emergency exits shut. Reuse of one part doesn't mean they reused as many as possible. Weight and maintenance are much larger issues than maximizing parts commonality.
Look at the video I posted earlier of the emergency exit in motion. It folds down about 140 degrees. The plug hinge does not have that range of motion.
In my opinion, its pretty obvious that the hinges are different between the plug and the door. And I can tell that from the exit door photo above and any of the dozens of mid exit plug photos like the one in post 843. In fact, stop pin fittings, guide fittings and the perimeter frame they attach to seem to be about the extent of common parts between the plugs and exit doors.
Does that prove they they use different springs. Nope. But it does prove that it cant be assumed that are even springs involved in the exit door hinges. And I haven't seen any photographs that prove the exit doors have similar hinges to the plugs.
Why are the guide fittings identical? Perhaps they didn't see a need to have different parts that serve the same purpose, that is guiding the door up on a bearing in the frame. Perhaps they didn't see a risk that someone would try to bolt an exit shut. Perhaps they do bolt the inactivated emergency exits shut. Reuse of one part doesn't mean they reused as many as possible. Weight and maintenance are much larger issues than maximizing parts commonality.
The door plug has no design features like that, it looks like if you released it when open it would simply fall open until the goosenecks strike the lower sill. You probably have to handle it with care to ensure it doesn't accidentally fall open and damage the sill.
So the hinge apparatuses are quite different between the two, but I don't think you can conclude from that whether or not individual parts, like the springs, are different.
It's just my feeling that the springs would be different on the lighter door, but it's also possible they are less compressed, which would also reduce the lift force. Or maybe the same spring with the same compression works well enough.
Springs are easy enough to source that having a different one on the door plug wouldn't be a big deal.
The most likely scenario is that the bolts were not installed. There is broad agreement on that aspect. If the lower bolts were installed not only would the door not move up, but even if there were no nuts on bolts, the bolts would be trapped [by] the spring pressure and would not fall out. In the NTSB briefing they stated that the door moved up before it was ejected. As noted that cannot happen if the lower bolts were in place..........Based on these conditions there is only one conclusion, that is: None of the four locking bolts were present at the time the door was ejected.
No damage to the outboard side of the track means that the bolts weren't there in the first place..........I don't believe that it is possible for this event to happen if any two of the safety bolts are installed. This provides a level of redundancy to the design. As has been noted this basic design has been employed on the previous generation 737 and flown for millions of hours with no known previous issues. That alone verifies the fundamental soundness of the basic design.
No damage to the outboard side of the track means that the bolts weren't there in the first place..........I don't believe that it is possible for this event to happen if any two of the safety bolts are installed. This provides a level of redundancy to the design. As has been noted this basic design has been employed on the previous generation 737 and flown for millions of hours with no known previous issues. That alone verifies the fundamental soundness of the basic design.
And after many years at my first employment - nothing to do with car production - it was discovered that one of our colleagues was not doing his job properly - instead of removing and bringing down all the broadcast antennas and dishes that we rigged on the roof of an outside broadcast event, he would leave them up there so the kit would be there for the next event and he wouldn't have to carry it all the way down and back up again. But the next event might have been a year away ! So we had a continual problem with some of our gear not being in the stores when it should have been there, and the reason was this bloke.
I suspect this aircraft manufacturer - or its subcontractors - has both problems; The new bosses have seemingly focussed on making money rather than airliners, so they don't care about their staff and and have accordingly cut costs so much that the dedicated engineers and technicians have left, or retired and not been replaced, and those who remain are disillusioned and don't care, or are not properly trained in the first place.
And the apparent lack of double inspections etc, is presumably 'allowing' corners to be cut unnoticed. I can imagine a worker like my ex colleague saving time by installing this blank plug without these four locking bolts, and signing himself off, with nobody ever knowing, or noticing or inspecting.
I sincerely hope I am wrong !
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We've established that the door plug weighs around 65 lb. How much heavier do you think a live door with the latching mechanism, slide and vent panel weighs ?
Say 50% more, around 100 lb ?
Don't you think some assistance to lift it up in order to open it, in an emergency, would be a good idea ? The initial design of the live door reportedly didn't have any assistance, and then Boeing thought better.
Say 50% more, around 100 lb ?
Don't you think some assistance to lift it up in order to open it, in an emergency, would be a good idea ? The initial design of the live door reportedly didn't have any assistance, and then Boeing thought better.
It appears to me on the E/E door that has the decal NOT an Exit as re-posted in #870; at the lower sides there looks likely a roller fitting on the door frames and a guide block on the aperture frames, which faces upwards! that
Of course it could be a micro-switch block on the aperture.
Of course it could be a micro-switch block on the aperture.
Last edited by aeromech3; 13th Jan 2024 at 10:55. Reason: further look
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And on the bottom right there is something that looks like a spring, with something shiny at the top, possibly a spring around another damper:
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MAX9 with mid-aft e/e delivered at +/- same time
On a different note, I thought that the plug was first applied by Boeing on the NG-900ER (since 2007), but I now found that Boeing started plugging exits as early as 1970 with the advent of the "Advanced" 727-200. The earlier version (delivered 1967 through 1969) had pre-wing type 2 exits, while these were replaced by plugs on the "Advanced". So, the plug has quite some history at Boeing....
Regards
https://www.airliners.net/photo/Unit...27-222/1117348
https://www.airliners.net/photo/Unit...-222/2079350/L
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Door closing instructions
I'd like to see a page from the maintenance guide describing how to close and secure the door! And if any tools are used to lower and hold closed the door while the bolts are fitted.
Does the lift assistance have to be built into the hinge? Could it perhaps be built into the latching mechanism? Could the latching mechanism cam the door upwards with the help of springs integrated into the latching mechanism? Could that be what the visible springs around the view port in the emergency exit photo assist with?
I can't seen anything on any of the (admittedly poor) photos that resembles the above.
D Bru you are not entirely wrong, but the B727-200ADV which I worked on, did not have the removable plug we are discussing; it was a total fuselage plug which made it a longer aircraft.
Not sure of the history of this particular B727.
Not sure of the history of this particular B727.
I would say more a case of "There are probably some ex Boeing quality people who retired in disgust who wouldn't mind coming back as an overseer in the spirit of making sure the work is being done properly". They might only see that as possible when being paid and managed independently of Boeing.