Alaska Airlines 737-900 MAX loses a door in-flight out of PDX
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DTA OK, now that I can post images, these a couple of images that are available.
You can just about see what look like bushes that locate inside the slots in the rear green bracket. I have zoomed and image enhanced it in the next image. The bushes themselves are not completely clear but the shadow from them is.
You can just about see what look like bushes that locate inside the slots in the rear green bracket. I have zoomed and image enhanced it in the next image. The bushes themselves are not completely clear but the shadow from them is.
I popped the colours in this image to make it easier to see things. The one end pad location where the bolt appears to have lost its head is intact. So end pad was strong enough to pull the head off the bolt. The other end pad, where the bolt still has it's head, is missing. The bolt was strong enough to fracture the end pad in shear/bending.
It's not surprising that those failed in tension. There will be a moment on the fitting when the hinge post is pulling "down" (in the door coord system), putting the top fasteners (these two) in tension and the bottom ones in compression. Except fasteners don't take compression, that goes through contact pressures between the fitting and frame. The bottom bolts probaby failed in shear, bearing tear-out, or prying, or some kind of mixed mode.
On the other side it probably looks similar...maybe? It's hard to predict with wild failure processes like this. Some have theorized some or all of these 8 bolts were missing (4 fwd 4 aft) but I'm pretty sure the NTSB would have mentioned that by now.
The grey square where the fitting contacted the frame web is sealant.
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Proportion -900ERs with door plug option
I think it's as simple as the fact that the last -900ER was delivered nearly 5 years ago, so will almost certainly have undergone one or more scheduled maintenance checks that would have revealed any anomalies by now.
Incidentally, does anyone know roughly what proportion of -900ERs have the door plug ?
Incidentally, does anyone know roughly what proportion of -900ERs have the door plug ?
Out of some 500+ 900ERs produced, well over 400 are likely to have the door plug option. This could be actually slightly lower because United's are not all "plugged", related to absorbing Continental. One would have to check each of the 136 United -900ERs, but even if it's half of them plugged, there's still well over 60% (330 out of 500 smthing) overall plugged.
Alaska airlines 79
Delta 172
El Al 8
Korean 6
Turkish 15
Ukraine Intl 1
United 136
Windrose 1
I think it's as simple as the fact that the last -900ER was delivered nearly 5 years ago, so will almost certainly have undergone one or more scheduled maintenance checks that would have revealed any anomalies by now.
Incidentally, does anyone know roughly what proportion of -900ERs have the door plug ?
Incidentally, does anyone know roughly what proportion of -900ERs have the door plug ?
Regarding this feedback from Dave in #651, do airliners typically all get stripped down to the frame for inspection of fittings before the 5 year mark? If anomalies such as missing bolts are found during such maintenance, who becomes informed of that? Just the airline itself? The regulator in that country? Boeing (or Airbus etc) as manufacturer? I haven't yet read other threads which I realise probably clarify that.
If one believes that the door plug cannot open without moving up, and one believes that the stop bolts should prevent it moving up, then any other fastener damage is likely caused the the severe airloads (outflow and slipstream) after the plug opened and is not the cause of it opening.
The bottom hinges could have been completely missing from the aircraft. That would make the door plug harder to install but that defect would not enable the door plug to open if the upper two locking bolts were in place and the stop fittings overlapped as intended.
Probably obvious to most but seems to be causing a diversion from the main question. Were the locking bolts installed?
The bottom hinges could have been completely missing from the aircraft. That would make the door plug harder to install but that defect would not enable the door plug to open if the upper two locking bolts were in place and the stop fittings overlapped as intended.
Probably obvious to most but seems to be causing a diversion from the main question. Were the locking bolts installed?
...Regarding feedback from Dave in #651, do airliners typically all get stripped down to the frame for inspection of fittings before the 5 year mark? If anomalies such as missing bolts are found during such maintenance, who becomes informed of that? Just the airline itself? The regulator in that country? Boeing (or Airbus etc) as manufacturer? I haven't yet read other threads which I realise probably clarify that.
https://www.abc.net.au/news/2024-01-...wout/103306160
Which has, in part:
"...Boeing has checked the service records of earlier Boeing 737-900ER aircraft that had a similar door plug, but all have undergone extensive maintenance since being delivered and none has shown a sign of similar problems, sources said."
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If they where installed one would question the way they where installed. A bolt trough holes in 2 pieces of metal have a tendency to pull those metal pieces towards each other when tightened. Did these bolts have sleeves on them on the middle to prevent this. If no sleeves the bolts themselves would be hit with force by the rollers they tried to keep in place and bolts don't really like to be hit repeatedly on their middle, even by vibration or if they are thermally hardened. Bolts are there to keep things together and to a degree keep stuff from moving laterally but only if the stuff is kept tight together, not if there is space for movement. So metal fatigue in the bolts could still be an issue here which could be checked by looking for deformation or nicks on the rollers if the bolts can't be found.
It is my understanding that an identical locking method was used on door plugs on aircraft that have been in service for several years. If that is true it seems unlikely that the same locking method would fail so quickly on this aircraft. The elephant is not just in the room, it fills the room.
I come from a background of military service (engineering), as I’m sure many others of us have, and so clearly recall the absolute importance of checks, independent inspections, signatures and so on. It was drummed into us, repeatedly. And this was largely on jets carrying 1 or 2 persons, not commercial aircraft carrying hundreds.
Looking at the retainers For the door/plug I am at a loss as to how, with 12 of those on a 1 M2 door, with a legacy back to the 707 as to design, it could have failed, unless somebody just didn’t put it together….
Psychophysiological entity
I suppose it's possible that during transit doors and plugs might well follow different rules. However, it's been stated that the plugs were removed to facilitate the loading of seats etc., so the concept of a plug being 'in for life' just can't be right. It's been said they're not removed for painting, though I'm very uncertain about that. Surely the paint would have to go around the edges?
If I were overseeing this, I'd have the door/plug flagged with something like: 'Temporarily fitted ONLY'. The guy with the trim is in his own world and the hole soon disguised.
If I were overseeing this, I'd have the door/plug flagged with something like: 'Temporarily fitted ONLY'. The guy with the trim is in his own world and the hole soon disguised.
Missing Negative G Bolts on MAX9
Best illustration and explanation and of plug retention is in Seattle Times at NTSB focus on Boeing, Spirit assembly work after Alaska Airlines blowout | The Seattle Times
It poses question “What could cause the Boeing 737 MAX 9 door plug to detach during flight?”. Answer is four missing bolts. NTSB says they were missing but is coy about why.
On ground and in smooth flight these bolts are completely inconsequential. They are not under any load, just sit in their holes doing nothing.
But the bolts have a hidden function. Under negative G and without cabin pressure they are all that hold plug from slipping out of its guide tracks and being torn from the aircraft.
If you have difficulty visualising negative G just consider retention mechanism turned upside down. It doesn’t work.
Even under negative G, bolts are very lightly loaded; not more than 100 kg. So they did not break.
A single bolt is enough to keep door in place. It’s inconceivable that all four fell out, so obviously they weren’t installed.
Missing bolts become really dire when you take account of springs on lower hinge. They are there to take most of plug’s weight during its installation.
Let’s guess some figures - weight of door 50 kg, thrust of springs 40 kg. Mechanics must exert 10 kg to lift plug, insert guide tracks over rollers on door frame and then lower plug into position.
Now consider what happens when aircraft encounters a little turbulence. At a modest 0.8 G, weight of plug goes down to 40 kg and springs can jiggle it off rollers and out of aircraft.
That’s why missing bolts are so much more crucial than they may seem.
Let’s call them “Negative G Bolts” to reflect their true significance
Best illustration and explanation and of plug retention is in Seattle Times at NTSB focus on Boeing, Spirit assembly work after Alaska Airlines blowout | The Seattle Times
It poses question “What could cause the Boeing 737 MAX 9 door plug to detach during flight?”. Answer is four missing bolts. NTSB says they were missing but is coy about why.
On ground and in smooth flight these bolts are completely inconsequential. They are not under any load, just sit in their holes doing nothing.
But the bolts have a hidden function. Under negative G and without cabin pressure they are all that hold plug from slipping out of its guide tracks and being torn from the aircraft.
If you have difficulty visualising negative G just consider retention mechanism turned upside down. It doesn’t work.
Even under negative G, bolts are very lightly loaded; not more than 100 kg. So they did not break.
A single bolt is enough to keep door in place. It’s inconceivable that all four fell out, so obviously they weren’t installed.
Missing bolts become really dire when you take account of springs on lower hinge. They are there to take most of plug’s weight during its installation.
Let’s guess some figures - weight of door 50 kg, thrust of springs 40 kg. Mechanics must exert 10 kg to lift plug, insert guide tracks over rollers on door frame and then lower plug into position.
Now consider what happens when aircraft encounters a little turbulence. At a modest 0.8 G, weight of plug goes down to 40 kg and springs can jiggle it off rollers and out of aircraft.
That’s why missing bolts are so much more crucial than they may seem.
Let’s call them “Negative G Bolts” to reflect their true significance
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Excellent analogy, I believe you are 100% correct.
Definitely the bolts were missing, all the discussion of loose bracket retention bolts tearing through brackets is just a red herring, a consequence of the panel flopping into the airstream at over 200 knots.
Definitely the bolts were missing, all the discussion of loose bracket retention bolts tearing through brackets is just a red herring, a consequence of the panel flopping into the airstream at over 200 knots.
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Might add another here … pax and service door removal to enable getting large interior components in (like galley and other units) is much more complex than a simple plug but is done also. Reasons for that can be multiple, for example to enable a higher assembly and output rate.
So doing IT is NO issue at all. The way you do it and the way it is controlled is where things certainly have gone wrong (loose bolts and …. And …). If that is the main cause is not known yet. To me the design does not feel solid yet either.
Would also be interesting to find out if the manufacturing processes in this respect were changed for -9 and for production rate ramp-up.
In an earlier post I mentioned that it would be wise to add a WG for Manufacturing Processes/Procedures and more to the NTSB investigation. I don’t know if the (high reputation) NTSB has the required specialists. Experience tells you not to assume things.
Still remember the US congressional hearings on the MAX, when Mr D was FAA Admin, and nobody at the table had ANY design experience let alone any manufacturing engineering (ME by DEF covering manufacturing, tooling, production (including final assembly), global logistics, etc) experience and certainly not at the expert level that was required even early on. No global gold standard there ;-)
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some thoughts, apologies for unseen repeats
Plug seems over-engineered. Why complex hinge, guides and stopper pads when 12 studs/captive bolts with castellated nuts and cotter pins could suffice, redundancy built-in. Not much to inspect except seals and corrosion so infrequent maintenance requirement, can't see labour-saving being significant.
3 previous flights with master caution and cabin pressure warnings on a new AC - by the 3rd occurrence Alaska should have grounded it until they found out exactly why, lessons from MCAS still needed. Scheduling a future inspection and cancelling ETOPS indicates unfit for purpose risk assessment, insufficient regulation/compliance standards. With cabin pressurisation a life-critical system, Boeing, FAA and Alaska all have responsibility.
As FAA production license holder, ultimate responsibility for verifying correct plug installation lies with Boeing, regardless of Spirit's PMA license, $5bn revenue or employee class action filed December.
jacobinDOTcom/2024/01/alaska-airlines-boeing-parts-malfunction-workers-spirit-aerosystems
Homendy's recent appearance is not the solid engineering & production leadership needed to build confidence across US aviation. Not even starting on her background and politics of the appointment.
The language is anything but clear. To understand "plug" look in a sink or bath - this door panel is not a plug, but could easily have been, in which case this incident wouldn't have happened. Never come across a door panel "translating" anywhere, is that just American speak or did the NTSB lawyers instruct using new words lacking any jurisprudence to offset liability ?
Indonesia transport ministry just grounded Lion Air's 3 Max 9s despite them having active emergency exits and not plugs. Boeing confidence is spiralling, opposite way to insurance premiums I expect.
O'Leary's recent comments surprisingly clean after that 2022 Boeing tirade. Looks like he's still holding out for the €100M bonus, can't see it with the delayed 220+ 737 deliveries.
wwwDOTirishtimesDOTcom/business/2024/01/09/ryanair-boss-calls-on-boeing-to-improve-quality-control-after-mid-flight-accident/
Slainte
Plug seems over-engineered. Why complex hinge, guides and stopper pads when 12 studs/captive bolts with castellated nuts and cotter pins could suffice, redundancy built-in. Not much to inspect except seals and corrosion so infrequent maintenance requirement, can't see labour-saving being significant.
3 previous flights with master caution and cabin pressure warnings on a new AC - by the 3rd occurrence Alaska should have grounded it until they found out exactly why, lessons from MCAS still needed. Scheduling a future inspection and cancelling ETOPS indicates unfit for purpose risk assessment, insufficient regulation/compliance standards. With cabin pressurisation a life-critical system, Boeing, FAA and Alaska all have responsibility.
As FAA production license holder, ultimate responsibility for verifying correct plug installation lies with Boeing, regardless of Spirit's PMA license, $5bn revenue or employee class action filed December.
jacobinDOTcom/2024/01/alaska-airlines-boeing-parts-malfunction-workers-spirit-aerosystems
Homendy's recent appearance is not the solid engineering & production leadership needed to build confidence across US aviation. Not even starting on her background and politics of the appointment.
The language is anything but clear. To understand "plug" look in a sink or bath - this door panel is not a plug, but could easily have been, in which case this incident wouldn't have happened. Never come across a door panel "translating" anywhere, is that just American speak or did the NTSB lawyers instruct using new words lacking any jurisprudence to offset liability ?
Indonesia transport ministry just grounded Lion Air's 3 Max 9s despite them having active emergency exits and not plugs. Boeing confidence is spiralling, opposite way to insurance premiums I expect.
O'Leary's recent comments surprisingly clean after that 2022 Boeing tirade. Looks like he's still holding out for the €100M bonus, can't see it with the delayed 220+ 737 deliveries.
wwwDOTirishtimesDOTcom/business/2024/01/09/ryanair-boss-calls-on-boeing-to-improve-quality-control-after-mid-flight-accident/
Slainte
Last edited by Senior Pilot; 11th Jan 2024 at 00:18. Reason: Remove offensive and OT quote
Removing door-size items in final assembly (one or more times) is SOP in manufacturing for many types of aircraft for multiple types of reasons and has been for an age. I mentioned a few reasons in an earlier post.
Might add another here … pax and service door removal to enable getting large interior components in (like galley and other units) is much more complex than a simple plug but is done also. Reasons for that can be multiple, for example to enable a higher assembly and output rate.
Might add another here … pax and service door removal to enable getting large interior components in (like galley and other units) is much more complex than a simple plug but is done also. Reasons for that can be multiple, for example to enable a higher assembly and output rate.
It makes little sense to remove an emergency exit door plug to install the interior because the door is relatively small and most of the bits wouldn't fit. They use the forward and aft main doors. Many of the interior parts are large/bulky, and they want as much room as possible to move them because they are literally manhandled onto the aircraft. A smaller door is just an invitation to damaging either the door or the interior bits when moving them around.
Actual doors are different - they are routinely opened, both during final assembly and on the flight line to provide ventilation, etc. of the cabin. Doors are designed to be repeatedly opened/closed without requiring repeated rigging and adjustments - door plugs aren't.
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Missing Negative G Bolts on MAX9
Best illustration and explanation and of plug retention is in Seattle Times at NTSB focus on Boeing, Spirit assembly work after Alaska Airlines blowout | The Seattle Times
It poses question “What could cause the Boeing 737 MAX 9 door plug to detach during flight?”. Answer is four missing bolts. NTSB says they were missing but is coy about why.
On ground and in smooth flight these bolts are completely inconsequential. They are not under any load, just sit in their holes doing nothing.
But the bolts have a hidden function. Under negative G and without cabin pressure they are all that hold plug from slipping out of its guide tracks and being torn from the aircraft.
If you have difficulty visualising negative G just consider retention mechanism turned upside down. It doesn’t work.
Even under negative G, bolts are very lightly loaded; not more than 100 kg. So they did not break.
A single bolt is enough to keep door in place. It’s inconceivable that all four fell out, so obviously they weren’t installed.
Missing bolts become really dire when you take account of springs on lower hinge. They are there to take most of plug’s weight during its installation.
Let’s guess some figures - weight of door 50 kg, thrust of springs 40 kg. Mechanics must exert 10 kg to lift plug, insert guide tracks over rollers on door frame and then lower plug into position.
Now consider what happens when aircraft encounters a little turbulence. At a modest 0.8 G, weight of plug goes down to 40 kg and springs can jiggle it off rollers and out of aircraft.
That’s why missing bolts are so much more crucial than they may seem.
Let’s call them “Negative G Bolts” to reflect their true significance
Best illustration and explanation and of plug retention is in Seattle Times at NTSB focus on Boeing, Spirit assembly work after Alaska Airlines blowout | The Seattle Times
It poses question “What could cause the Boeing 737 MAX 9 door plug to detach during flight?”. Answer is four missing bolts. NTSB says they were missing but is coy about why.
On ground and in smooth flight these bolts are completely inconsequential. They are not under any load, just sit in their holes doing nothing.
But the bolts have a hidden function. Under negative G and without cabin pressure they are all that hold plug from slipping out of its guide tracks and being torn from the aircraft.
If you have difficulty visualising negative G just consider retention mechanism turned upside down. It doesn’t work.
Even under negative G, bolts are very lightly loaded; not more than 100 kg. So they did not break.
A single bolt is enough to keep door in place. It’s inconceivable that all four fell out, so obviously they weren’t installed.
Missing bolts become really dire when you take account of springs on lower hinge. They are there to take most of plug’s weight during its installation.
Let’s guess some figures - weight of door 50 kg, thrust of springs 40 kg. Mechanics must exert 10 kg to lift plug, insert guide tracks over rollers on door frame and then lower plug into position.
Now consider what happens when aircraft encounters a little turbulence. At a modest 0.8 G, weight of plug goes down to 40 kg and springs can jiggle it off rollers and out of aircraft.
That’s why missing bolts are so much more crucial than they may seem.
Let’s call them “Negative G Bolts” to reflect their true significance
- Per NTSB the door plug weighs only 63 lbs
- Per Chris Brady videos the springs are designed to prevent the door/plug from closing and falling back behind the stops after it has been opened. Therefore, they will not allow the door plug to fall back down behind the stops from gravity alone.
- The tethers hold the door plug open at 15 degrees and in photos the uncompressed springs carry the entire weight of the plug.
- If Boeing recycles the spring part (unknown) from actual emergency doors which are much heavier with slides and levers and machinery, those springs would need to carry the entire weight of the door.