Alaska Airlines 737-900 MAX loses a door in-flight out of PDX
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It does seem surprising to me that an airframe with known pressurisation issues wasn't taken out of service right away. It also seems odd to me that two seats next to the relevant window were apparently empty, two of only seven unoccupied seats in a full flight - including a window seat at that. That suggests that these seats were not bookable, which further suggests that something was known about that area of seating. Whistling noises? Rattling? Cold breeze?
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I was second guessing myself and was correct the first time. This image of a DOOR shows the locking pins below the upper two striker plates which have the guide pin between them.
But it does look like the PLUG has bolts in a different location, possibly going into the guide pin.
But it does look like the PLUG has bolts in a different location, possibly going into the guide pin.
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I agree all speculation. But on the face of it there doesn't seem to be much redundancy or a clear flag/indicator that the door.is flight ready and secure like the normal human operated doors.
The door plug, on the other hand, is only ever going to be removed in the hangar, during a check, and it's going to have to be lifted out anyway once it's cleared the stops, so the value of the springs, if fitted, would be minimal.
And yet, both the door and the plug have roughly the same shape of frame -- and the frame is missing on the accident aircraft with at least the top four (out of twelve) bolts sheared off where it connects to the fuselage from the inside. Are those bolts the primary mechanism to keep the frame of the door/plug attached to the aircraft, or would you expect them to shear off?
Psychophysiological entity
Is there confusion between "sheared bolts" and permanently inserted steel surface pressure-bearing rods set into the castings?
Note the two rods that slide in the casting with the lock bolts (or missing lock bolts). It's been suggested (kghjfg) that they are too short for all fuselage stressed states. I note one can see a wear mark indicating how far into the sliding slot they have been sitting. There's a lot of wasted length.
Note the two rods that slide in the casting with the lock bolts (or missing lock bolts). It's been suggested (kghjfg) that they are too short for all fuselage stressed states. I note one can see a wear mark indicating how far into the sliding slot they have been sitting. There's a lot of wasted length.
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Question
Have they found the door/plug and any related parts that blew out yet? I imagine that there will be some telling evidence if a loose bolt pulled out of a bracket. Or no damage if the bolt was never installed.
And yet, both the door and the plug have roughly the same shape of frame -- and the frame is missing on the accident aircraft with at least the top four (out of twelve) bolts sheared off where it connects to the fuselage from the inside. Are those bolts the primary mechanism to keep the frame of the door/plug attached to the aircraft, or would you expect them to shear off?
Where did you find any photo that shows the fuselage side stop pads are sheared off?
I think Chris misspoke; not a big deal for the pressure from the interest in the topic. The door is stopped from moving down by the top of the slot in the door guide. I think he missed that the closeup was of the other side of the door than he expected as the rest of the diagram labels are correct, showing the door moving up to disengage.
Psychophysiological entity
It would seem from his post that the bottom two bolts would also have to be missing to allow the roller pins to move down the guide tracks.
However, if they were, the lift springs would allow the door to be lifted - unless the top bolts were never fitted. So, never any top bolts and the loss of perhaps only one lower bolt. The most far-fetched scenario. But, those spring must be very strong - with all that implies.
However, if they were, the lift springs would allow the door to be lifted - unless the top bolts were never fitted. So, never any top bolts and the loss of perhaps only one lower bolt. The most far-fetched scenario. But, those spring must be very strong - with all that implies.
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I think Chris misspoke; not a big deal for the pressure from the interest in the topic. The door is stopped from moving down by the top of the slot in the door guide. I think he missed that the closeup was of the other side of the door than he expected as the rest of the diagram labels are correct, showing the door moving up to disengage.
So, without the bolts, the springs on the hinges are going to be doing their best to free the plug from the guide tracks, and are very likely to succeed before very long. I wonder how many cycles this aircraft had in a bit more than two months..
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In the latest video the springs are shown compressed. See the 10:12 time mark or so and the spring kinda snakes side to side as compression springs (which are labeled) tend to do if they don't have tight guides.
That double nut cap washer should have been able to retain the bottom part of the door or at least hang on well enough to twist the hinges, but no such damage is evident.
That double nut cap washer should have been able to retain the bottom part of the door or at least hang on well enough to twist the hinges, but no such damage is evident.
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On the DOOR the guide pins are just that, guides to stop damage to the pads. The top of the door is stopped from moving out by the guides until the stops have cleared the pad structure. Remember thare are no pressurisation loads on the DOOR at this point, the vent panel is open.
The DOOR is stopped from moving up by locking pins that are pelow the viewport between the second and third stops / pads.
It appears that on the PLUG there are no locking pins, just 4 bolts. Two apparently going through the guides and into the pins (near top of door) and two at the hinge / springs at the bottom of the door which I've seen no detail of.
Looking like the top bolts at least were not fitted. They would not be highly loaded, at most opposing the force of the lift springs.
There is however another possibility:
Some or all of the Stops / Pads were not adjusted correctly leaving the guide pins and locking bolts carrying presurisation loads leading to failure from low cycle fatigue.
EDIT: just found latest youtube info
This shows the bolts through the guide track and details of the lower bolts. Looks ike either all bolts were missing or the stops / pads were mis-adjuated causing pressurisation loads on the guides and guide pins.
The DOOR is stopped from moving up by locking pins that are pelow the viewport between the second and third stops / pads.
It appears that on the PLUG there are no locking pins, just 4 bolts. Two apparently going through the guides and into the pins (near top of door) and two at the hinge / springs at the bottom of the door which I've seen no detail of.
Looking like the top bolts at least were not fitted. They would not be highly loaded, at most opposing the force of the lift springs.
There is however another possibility:
Some or all of the Stops / Pads were not adjusted correctly leaving the guide pins and locking bolts carrying presurisation loads leading to failure from low cycle fatigue.
EDIT: just found latest youtube info
Last edited by Thruster763; 7th Jan 2024 at 19:14. Reason: new info
I note that all 4 bolts are retained by castle nuts and cotter pins (more usually known as split pins). Had those been correctly assembled, I can't see any way that the door plug could have let go. Incorrect assembly could be any of:
a) omitting the split pins
b) omitting the nuts and therefore the split pins
c) omitting the bolts and therefore the nuts and split pins
at any or all of the 4 bolt locations.
Any thoughts?