Alaska Airlines 737-900 MAX loses a door in-flight out of PDX
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The lock bolts feed from outside in, with somewhat tight quarters to accomplish. As a mechanic, I would probably close the door, push down against the springs, and temp insert one bolt in reverse fashion to hold the door in place while I got the others bolts installed the proper way, and then flip around the temp installed bolt. Obviously if there was a break or end of shift or whatever after the temp bolt was installed, you can see how this could happen. But... this possibility still means there is a pretty crappy QA system.
Psychophysiological entity
Something just doesn't seem right about that hinge assembly.
my bold.
That nylon type material has to slide over the black hinge pins, therefore the holes though them must be very nearly as big as the washers under the pairs of bronze-coloured nuts. This makes me assume that the hinge guides are not designed to thump against, or have sustained pressure on, the washers.
Clearly the nylon type material does not slide over the washers, indeed one is reported as having belled up during the 'accident'. Presumably the nuts have to be removed to lift the plug away from the aircraft, so why are the washers so small in diameter?
Dragon6172. That's why I never throw worn PK screwdrivers away. Turned and tapered for a repetitive job makes them valuable. But then, Spirit or Boeing would have those tools . . . wouldn't they?
Physics and photos prove the spring force applied is > 31.5 lb each spring, > 63 lb from the pair, when the springs are extended to the stop washers at the end of the hinges
That nylon type material has to slide over the black hinge pins, therefore the holes though them must be very nearly as big as the washers under the pairs of bronze-coloured nuts. This makes me assume that the hinge guides are not designed to thump against, or have sustained pressure on, the washers.
Clearly the nylon type material does not slide over the washers, indeed one is reported as having belled up during the 'accident'. Presumably the nuts have to be removed to lift the plug away from the aircraft, so why are the washers so small in diameter?
Dragon6172. That's why I never throw worn PK screwdrivers away. Turned and tapered for a repetitive job makes them valuable. But then, Spirit or Boeing would have those tools . . . wouldn't they?
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I agree, BUT Boeing probably have a written procedure for closing and securing this door and they probably have some special tools for the job. There might be a handle to assist closing and lowering the door and a temporary method for holding it in place while the arrestor bolts are fitted. Mechanics are nor expected to just wing it!
In Chris Brady's videos, he rightly labels them "lift assist springs". It's someone either inside or outside of the aircraft, pulling down the actuation lever, that provides the additional force required to lift the door off the rollers. The springs were originally fitted because of the difficulty in opening the door purely by brute force.
The full weight of the plug is carried by the extended springs. Whether they are called lift "assist" or not, they support the entire weight of the plug when they are fully extended.
Once lifted, the plug will not fall back down below the stop fittings because its entire weight is being supported
If the springs applied less than the mass of the plug, then
the Hinge Guide Fittings would not be held against their upper stop washers when supporting the weight of the plug
one would need to lift the plug over the stop pads to close the plug
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"It is time to re-examine the delegation of authority and assess any associated safety risks," FAA Administrator Mike Whitaker said. "The grounding of the 737-9 and the multiple production-related issues identified in recent years require us to look at every option to reduce risk. The FAA is exploring the use of an independent third party to oversee Boeing’s inspections and its quality system."
The regulator may actually be getting serious about this.
Something just doesn't seem right about that hinge assembly.
...
That nylon type material has to slide over the black hinge pins, therefore the holes though them must be very nearly as big as the washers under the pairs of bronze-coloured nuts. This makes me assume that the hinge guides are not designed to thump against, or have sustained pressure on, the washers.
Clearly the nylon type material does not slide over the washers, indeed one is reported as having belled up during the 'accident'. Presumably the nuts have to be removed to lift the plug away from the aircraft, so why are the washers so small in diameter?
...
That nylon type material has to slide over the black hinge pins, therefore the holes though them must be very nearly as big as the washers under the pairs of bronze-coloured nuts. This makes me assume that the hinge guides are not designed to thump against, or have sustained pressure on, the washers.
Clearly the nylon type material does not slide over the washers, indeed one is reported as having belled up during the 'accident'. Presumably the nuts have to be removed to lift the plug away from the aircraft, so why are the washers so small in diameter?
What I haven't seen are clear pictures of the slide-guide rod that seems to be missing that washer. I haven't heard of anyone finding the slide guide bracket that also went missing. Did it cone the washer and gut the nylon bushing or did it strip the nuts or break the threaded section?
I see from news today that at least one shoe and sock were removed from the passenger in the seat along the wall immediately behind the opening, though they did find his phone, also working, and returned to him via Alaska.
Part of the FAA Administrator's statement was that authority had been taken from the FAA by legislation, driving the move to self-certification. The link is to 1:39, but the forum doesn't start there.
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Something just doesn't seem right about that hinge assembly.
my bold.
That nylon type material has to slide over the black hinge pins, therefore the holes though them must be very nearly as big as the washers under the pairs of bronze-coloured nuts. This makes me assume that the hinge guides are not designed to thump against, or have sustained pressure on, the washers.
Clearly the nylon type material does not slide over the washers, indeed one is reported as having belled up during the 'accident'. Presumably the nuts have to be removed to lift the plug away from the aircraft, so why are the washers so small in diameter?
my bold.
That nylon type material has to slide over the black hinge pins, therefore the holes though them must be very nearly as big as the washers under the pairs of bronze-coloured nuts. This makes me assume that the hinge guides are not designed to thump against, or have sustained pressure on, the washers.
Clearly the nylon type material does not slide over the washers, indeed one is reported as having belled up during the 'accident'. Presumably the nuts have to be removed to lift the plug away from the aircraft, so why are the washers so small in diameter?
The Hinge Guide Fitting looks like a beefy chunk of steel and that is what ultimately would need to deform and slide over those washers. We know that the aft Hinge Guide Fitting was retained on the hinge pin while being ripped over the heads of at least 2 bracket bolts, and somehow escaping the other 2 bracket bolts, if they were present. In the below photo you can at least see the pin diameter relative to the stop washer, but the diameter of the hole in the Hinge Fitting Guide is obscured by the nylon washer.
I believe one of the Chris Brady videos states the maximum local wind specification for the plug (or door when installed). Definitely less than 271 KIAS.
Give Boeing engineers some credit, the self-ejecting plug design has breakaway features.
From Chris Brady video
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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 schadenfreude.
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What I haven't seen are clear pictures of the slide-guide rod that seems to be missing that washer. I haven't heard of anyone finding the slide guide bracket that also went missing. Did it cone the washer and gut the nylon bushing or did it strip the nuts or break the threaded section?
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At the risk of stating the obvious (again), they're called "lift assist springs" because, regardless of whether they can support the entire weight of the plug or not, their raison d'etre is to help lift the active door (which unsurprisingly weighs considerably more) over the stops and clear of the roller.
2) That is not the raison d'etre according to the Chris Brady videos, although they obviously assist the lifting of the plug or door.
The lock bolts feed from outside in, with somewhat tight quarters to accomplish. As a mechanic, I would probably close the door, push down against the springs, and temp insert one bolt in reverse fashion to hold the door in place while I got the others bolts installed the proper way, and then flip around the temp installed bolt. Obviously if there was a break or end of shift or whatever after the temp bolt was installed, you can see how this could happen. But... this possibility still means there is a pretty crappy QA system.
I do wonder if Alaska has any regrets about paying $100Ms to get our of their A320/321 leases early?
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If I were tasked with closing and securing that door, I might pull it inwards and push it down with one foot. Then I would an undersize bolt, welding rod, nail or similar in one of the four holes just to keep it in place while I positioned the proper bolts. If this had been done but the last step had been omitted, it might explain why it took so long for the incident to occur.
If I were working on my boat or RV I would pull the plug in from the top or middle for leverage, step on both hinges to counteract the spring, shove at least 1 bolt in the top to hold it against the spring force, then go about installing all the bolts.
But I suppose the installation/maintenance SOP may be more prescriptive in where to grab/pull/push for proper positioning.
These kinds of adaptations need to consider human factors in install/maintenance. If it were a door, that door would have a proper handle and latch and a logical "closing" sequence that naturally counteracts the springs. The fact that this is a plug adapted to the airframe may cause the technician to improvise.
But I suppose the installation/maintenance SOP may be more prescriptive in where to grab/pull/push for proper positioning.
These kinds of adaptations need to consider human factors in install/maintenance. If it were a door, that door would have a proper handle and latch and a logical "closing" sequence that naturally counteracts the springs. The fact that this is a plug adapted to the airframe may cause the technician to improvise.
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2) Of course the E/E door weight is significantly greater than the plug
3) We don't know if the springs for the E/E door are the same as those used for the plug, or if they have different part numbers and compression forces fit for purpose. You have stated that previously and I agree.
But there is absolutely no doubt the springs used for the plug support the weight of the plug. And as I said, according to Chris Brady, the design intent for the spring hinges, their reason to exist, is to prevent re-closing of the E/E door in the event of evacuation.
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At the very least, it would have been very simple to install a positional sensor flagging the existing annunciator in the flight deck. The plug cannot be ejected if it does not "translate" upwards more than a given amount which would be easy to detect if monitored.
(Some redundant attachment would have been appreciated as well!)
So many ways to break a chain of events...