3 month old 737-9 Max depressurisation incident

[YorkRailFan]

Seems a flawed design. Why would one not have it so it was plugged from inside and thus the pressure would hold it closed?

There is quite a history of outward opening doors causing trouble.

I don't think it's a design flaw based on the fact that the 737-900ER uses the same design and hasn't had this problem. I have a feeling that it's an installation issue.

 

[Tetchytyke]

Presumably though the previous groundings were the result of the general alert for the loose bolts issue, rather than something specific to the Alaska fleet?

I'm unsure- Alaska pulled 20 of the 737-900s out of service for urgent inspections, but other airlines were not affected to the same extent. But it was about the same time the missing nut/loose bolt issue in the rudder came to light.

 

[Brissle Girl]

I'm unsure- Alaska pulled 20 of the 737-900s out of service for urgent inspections, but other airlines were not affected to the same extent. But it was about the same time the missing nut/loose bolt issue in the rudder came to light.

Could be all down to delivery dates of the planes or where they were in terms of maintenance cycles.

 

[YorkRailFan]

We are grateful the Alaska Airlines crew performed the appropriate procedures to land the airplane with all passengers and crew safe. At Spirit AeroSystems, our primary focus is the quality and product integrity of the aircraft structures we deliver.

Spirit is a committed partner with Boeing on the 737 program, and we continue to work together with them on this matter. Spirit is following the protocols set by the regulatory authorities that guide communication in these types of circumstances and we will share further information when appropriate.

Spirit AeroSystems Statement – Alaska Airlines Flight 1282 | Spirit AeroSystems

www.spiritaero.com

Pretty lackluster statement from Spirit AeroSystems, nothing about working with regulators and airlines or about communicating with employees about this incident and potential steps forward.

 

[YorkRailFan]

The FAA has approved a method to comply with the FAA's Boeing 737-9 emergency airworthiness directive, and it has been provided to the affected operators.

The FAA’s priority is always keeping Americans safe. In that spirit, Boeing 737-9 aircraft will remain grounded until operators complete enhanced inspections which include both left and right cabin door exit plugs, door components, and fasteners. Operators must also complete corrective action requirements based on findings from the inspections prior to bringing any aircraft back into service.

The FAA will continue to support the National Transportation Safety Board’s investigation into Alaska Airlines Flight 1282. The NTSB is in charge of the investigation and will provide any updates.

https://www.faa.gov/newsroom/updates-grounding-boeing-737-max-9-aircraft

A positive step forward to get the 737-9 flying again.

This morning, Boeing issued a multi-operator message (MOM) which provided inspection details for the 737-9 MAX aircraft, which have been approved by the FAA. Two additional steps must occur before inspections can begin:

1. FAA must approve operators' inspection processes to ensure compliance (called an alternate means of compliance AMOC);
2. Alaska must develop detailed inspection instructions and processes for our maintenance technicians to follow.

As we await further information from the FAA and work through these important steps, our technicians have prepared each aircraft to be immediately ready for the required inspections when instructions are finalized.

We recognize that additional questions remain about the details of Flight 1282 that we are unable to address at this time. Because this is an active investigation, we must receive permission from the NTSB to provide information about the aircraft and its prior maintenance. We will provide additional information as soon as the NTSB permits us to do so.

As these steps remain pending, we will continue to experience disruption to our operations with these aircraft out of service. As of 8:30 a.m. Pacific, we have cancelled roughly 140 flights for Monday due to the 737-9 MAX grounding.

 

[YorkRailFan]

NTSB has recovered the door plug from Alaska Airlines Flight 1282 Boeing 737-9 MAX. NTSB investigators are currently examining the door plug and will send it to the NTSB Materials Laboratory in Washington, DC for further examination.

https://twitter.com/NTSB_Newsroom/status/1744442166116831560?t=zFgsIjtUMytWr1lG32fA3A&s=19

Hoping for a preliminary report soon.

 

[birchesgreen]

United have found loose bolts and other defects on some of it's 737MAX-9 plug doors.

United finds loose bolts on plug doors during 737 Max 9 inspections

United Airlines has found loose bolts and other parts on 737 Max 9 plug doors as it inspects its fleet of Boeing jets following the Friday rapid depressurization aboard an Alaska Airlines jet of the same make, according to three people familiar with the findings.

theaircurrent.com

Edit: second source i can quote

United Airlines finds loose bolts on multiple Boeing 737 Max 9 planes

Aircraft model has been grounded after a panel blew off an Alaska Airlines-operated plane mid-flight on Saturday

www.theguardian.com

United Airlines has found loose bolts and other “installation issues” on multiple 737 Max 9 aircraft, it said on Monday, referring to the Boeing model that has been grounded after a panel blew off an Alaska Airlines-operated plane mid-flight over the weekend.
https://www.theguardian.com/us-news...737-max-9-planes-after-mid-air-window-blowout
The industry publication Air Current reported that United found discrepant bolts on other parts on at least five panels that were being inspected following the accident. The US Federal Aviation Administration (FAA) and Boeing declined to comment.

“Since we began preliminary inspections on Saturday, we have found instances that appear to relate to installation issues in the door plug. For example, bolts that needed additional tightening. These findings will be remedied by our Tech Ops team to safely return the aircraft to service,” United said in a statement.

 

[Bletchleyite]

United have found loose bolts and other defects on some of it's 737MAX-9 plug doors.

United finds loose bolts on plug doors during 737 Max 9 inspections

United Airlines has found loose bolts and other parts on 737 Max 9 plug doors as it inspects its fleet of Boeing jets following the Friday rapid depressurization aboard an Alaska Airlines jet of the same make, according to three people familiar with the findings.

theaircurrent.com

I still see it as a flawed design. If it was a proper plug - inside the fuselage - the bolts could all have fallen out and it'd still not have failed.

It's the DC10 cargo door all over again.

The failsafe design of aircraft door or panel is one that is inside the fuselage. Other designs are inferior in safety terms.

 

[edwin_m]

I still see it as a flawed design. If it was a proper plug - inside the fuselage - the bolts could all have fallen out and it'd still not have failed.

It's the DC10 cargo door all over again.

The failsafe design of aircraft door or panel is one that is inside the fuselage. Other designs are inferior in safety terms.

I agree a door removed from the inside would be better - the reason can't be to avoid removing the interior panel, as that has to be removed anyway to get to the bolts that hold the plug in place.

However, the DC10 cargo door was re-designed and I don't believe there have been any such incidents since the 1970s, and this design of plug has apparently been used on pre-MAX 737s for some time. So I suggest it's unlikely to be a flawed design, more likely a material or assembly issue.

 

[najaB]

I still see it as a flawed design. If it was a proper plug - inside the fuselage - the bolts could all have fallen out and it'd still not have failed.

As I understand things, it is a plug design when it is in the normal position. The only (potential) flaw is that it is free to move down under gravity to the non-plug position.

This would be a non-issue though if the bolts are installed properly.

United have found loose bolts and other defects on some of it's 737MAX-9 plug doors.

The BBC article includes a picture of the recovered door from the Alaska aircraft:
https://www.bbc.co.uk/news/world-us-canada-67919436

 

[WatcherZero]

Alaska saying their inspections have now like United also found 'loose hardware' on 'a limited number of planes'.

 

[DustyBin]

As I understand things, it is a plug design when it is in the normal position. The only (potential) flaw is that it is free to move down under gravity to the non-plug position.

This would be a non-issue though if the bolts are installed properly.

This is my understanding too. The DC-10 cargo door was an inherently poor design (albeit fixable, evidently) whereas this is not.

There have been numerous instances of whistleblowing in relation to conditions on the MAX production line, so I wouldn’t be at all surprised if this is a simple QC issue (bolts not torqued correctly, missing pin retainers, bolts missing altogether etc.).

 

[YorkRailFan]

We continue to wait for final documentation from Boeing and the FAA before we can begin the formal inspection process.

As our maintenance technicians began preparing our 737-9 MAX fleet for inspections, they accessed the area in question. Initial reports from our technicians indicate some loose hardware was visible on some aircraft.

When we are able to proceed with the formal inspection process, all aircraft will be thoroughly inspected in accordance with detailed instructions provided by the FAA in consultation with Boeing. Any findings will be fully addressed in a matter that satisfies our safety standards and FAA compliance. The formal inspections will also require documenting all findings and those will be reported to the FAA. No aircraft will be returned to service until all of these steps are complete. The safety of these aircraft is our priority and we will take the time and steps necessary to ensure their airworthiness, in close partnership with the FAA.

Information about Alaska Airlines Flight 1282 - Alaska Airlines News

Latest updates & information can be found here.

news.alaskaair.com

Alaska Airlines has become the second airline to find loose bolts on their 737-9 aircraft, following fellow US carrier United. I don't think that this is the same as the emergency request by Boeing to check for loose bolts as that was for the fuselage more than the door plug.

 

[Tetchytyke]

this design of plug has apparently been used on pre-MAX 737s for some time. So I suggest it's unlikely to be a flawed design, more likely a material or assembly issue.

It can be both. A design which is safe when installed correctly but fails to an unsafe position is still a design flaw.

I’d agree with @Bletchleyite in that a plug should be installed from the inside, so that if the bolts fail the pressure differential keeps it in place.

Instead, in this case, if the bolts fail then the pressure differential causes the plug to get sucked off into the night sky.

 

[DustyBin]

It can be both. A design which is safe when installed correctly but fails to an unsafe position is still a design flaw.

I’d agree with @Bletchleyite in that a plug should be installed from the inside, so that if the bolts fail the pressure differential keeps it in place.

Instead, in this case, if the bolts fail then the pressure differential causes the plug to get sucked off into the night sky.

I’m not sure I agree to be honest.

The plug is fitted from the inside and pressure sealed whilst in the closed position. The bolts aren’t under any serious load, they simply stop the door moving. There’s basically zero chance of the bolts failing.

Aircraft have lost engines and windscreens for example due to missing or incorrectly fitted bolts; there’s only so much you can do to mitigate serious human error.

 

[Bletchleyite]

This is my understanding too. The DC-10 cargo door was an inherently poor design (albeit fixable, evidently) whereas this is not.

I'd say it was if it could drop into a position where it failed if just the bolts were loose or failed - safety is like a load of pieces of holed cheese, this design had only one layer. A failsafe design would be one where you had to lift it *up* against gravity to move it into the "unsafe" position.

 

[Tetchytyke]

Aircraft have lost engines and windscreens for example due to missing or incorrectly fitted bolts; there’s only so much you can do to mitigate serious human error.

Absolutely, and sometimes an unsafe failure is unavoidable. I suspect the cause will come down to poor quality control and poor construction line practices at Boeing.

But even the famous example of the BA flight 5390 cockpit windscreen failure was because the windscreen on the One-Eleven was fitted from the outside and secured against the fuselage, rather than from inside and pushed against the fuselage. If it had been a plug that was fitted from the inside then it wouldn't have moved. I do wonder if the same will apply here.

There's also the issue that the plug seemingly drops down into the position where it can be taken out from the outside, rather than having to be pushed up into that position.

It's also a timely reminder to always keep your seatbelt securely fastened whilst seated.

 

[najaB]

A failsafe design would be one where you had to lift it *up* against gravity to move it into the "unsafe" position.

Which would mean that the emergency exit would have to be lifted to open.

 

[Lost property]

Yes the 'Deactivated' variant they fit an emergency door but panel it over so you get a seat with no window. Then there is a couple of variations with the door active with sub variations by size of seats but primarily with an unsupervised door which is illegal in Europe or a door with a cabin attendant seat facing backwards installed in the row in front. The doors have interlocks which is slaved to the thrust controls and a locking bolt engages when the thrust lever is set to 58 degrees or higher and disengages when it isnt so they can only be opened (say by a rogue passenger) on the ground or during a landing.

Sorry, but that is complete rubbish.

Having ground run jet engines on types varying from FJ's to commercial types, I have yet to encounter any power settings measured in...degrees. Had you said EPR (Engine pressure ratio) or percent / rpm, this would have been correct. Neither have I ever encountered a door interlock as you describe it. And neither would there be a requirement to open doors during a landing.

If you have, please provide details of the aircraft type and, if possible, schematics showing how this works.

 

[Bletchleyite]

Absolutely, and sometimes an unsafe failure is unavoidable. I suspect the cause will come down to poor quality control and poor construction line practices at Boeing.

But even the famous example of the BA flight 5390 cockpit windscreen failure was because the windscreen on the One-Eleven was fitted from the outside and secured against the fuselage, rather than from inside and pushed against the fuselage. If it had been a plug that was fitted from the inside then it wouldn't have moved. I do wonder if the same will apply here.

There's also the issue that the plug seemingly drops down into the position where it can be taken out from the outside, rather than having to be pushed up into that position.

Bingo. The design was wholly reliant on the bolts. A different design (e.g. one where it had to be lifted up to release it, or where it was simply released inwards and removed that way) wouldn't have been - you may have got a slow pressure leak which would have been noticed eventually, but it wouldn't have blown out like that.

If there's an obvious way to mitigate for human error you do. This is nothing short of an awful design that thankfully didn't kill someone this time (but could have done had someone been in that seat or standing near the panel at the time).

 

[YorkRailFan]

Shouldnt be opened during the Wi-Fi installation, for all intents and purposes the plug is the external fuselage with 4 locking bolts over the four door runners so it cannot move and a couple of spring loaded pivoting arms at the bottom, there are no wiring looms or sensors running to the plug.

With the world's aviation spotlight firmly on the recent Alaska Airlines incident, various organizations that have worked on the aircraft have reaffirmed if their work related to anything near the 'plug door.' Aviation services firm AAR, contracted by the carrier to perform 2KU modification to enable inflight WiFi, noted it did not perform any maintenance near that part during its time onboard the aircraft in question - N704AL.

WiFi Installation Did Not Involve Door Of Alaska Airlines Boeing 737 MAX 9

Alaska Airlines aircraft in question, N704AL, was at an AAR facility in Oklahoma days before the mid-air incident.

simpleflying.com

Which has been conformed in this article that the door was not opened.

 

[Tetchytyke]

Which would mean that the emergency exit would have to be lifted to open.

Not necessarily- where there is an emergency exit on this aircraft in this position, it is a proper door, not a hatch, with a cabin crew member seated at it. It’s row 28 on the seating plan

 

[Bletchleyite]

Which would mean that the emergency exit would have to be lifted to open.

This isn't an emergency exit door. But the classic design of overwing emergency exit door used by Airbus is an inside plug that you open inwards and throw out.

It's also not unusual for aircraft doors to move in an "odd" way to ensure this sort of thing fails safe, e.g. turning the handle would lift it then push out.

 

[najaB]

Not necessarily- where there is an emergency exit on this aircraft in this position, it is a proper door, not a hatch, with a cabin crew member seated at it. It’s row 28 on the seating plan

True. But the idea is that the plug uses the same mounting points and sealing mechanism as the real exit door - in theory you can replace the plug with a door, though I don't know how common that will be in practice - so the emergency door would also have to be lifted to open it. It's worth noting that Boeing says that the exits are designed to be opened by passengers:

Although the MED exits are designed to be operated by passengers, a flight attendant will be stationed near them and will be able to focus on managing the evacuation of passengers throughout the mid-cabin area...

And "lift to open" isn't as intuitive as a door that falls to the open position when the lever/handle is activated.

Source: https://www.easa.europa.eu/en/downloads/97315/en

 

[Bletchleyite]

True. But the idea is that the plug uses the same mounting points and sealing mechanism as the real exit door

Which is called "doing it on the cheap". Indeed, like MCAS, the whole thing is doing it on the cheap - the more expensive and safer option would be not to have the gap at all unless the door is specified.

And "lift to open" isn't as intuitive as a door that falls to the open position when the lever/handle is activated.

It's perfectly possible to have the handle lift the door when it is operated. I've seen at least one aircraft door that does work that way.

 

[WatcherZero]

Sorry, but that is complete rubbish.

Having ground run jet engines on types varying from FJ's to commercial types, I have yet to encounter any power settings measured in...degrees. Had you said EPR (Engine pressure ratio) or percent / rpm, this would have been correct. Neither have I ever encountered a door interlock as you describe it. And neither would there be a requirement to open doors during a landing.

If you have, please provide details of the aircraft type and, if possible, schematics showing how this works.

15:45 explains the door interlocks

 

[najaB]

Which is called "doing it on the cheap". Indeed, like MCAS, the whole thing is doing it on the cheap - the more expensive and safer option would be not to have the gap at all unless the door is specified.

No, it wasn't "doing it on the cheap". It's about giving their customers (most of whom are lessors) the flexibility that they require to reconfigure the aircraft between operators. Having the mid-cabin doors means that the an airframe can be changed from a low-density configuration with a legacy carrier to a high-density configuration with a low-cost "sun and surf" holiday operator.

When the likes of AerCap order 150 737-Max aircraft they don't have specific operators in mind, so would run the risk of having too many of one version and not enough of the other.

 

[Bletchleyite]

No, it wasn't "doing it on the cheap". It's about giving their customers (most of whom are lessors) the flexibility that they require to reconfigure the aircraft between operators. Having the mid-cabin doors means that the an airframe can be changed from a low-density configuration with a legacy carrier to a high-density configuration with a low-cost "sun and surf" holiday operator.

Either way there was no need to have a design of door/plug with only one layer of safety - one set of bolts. That is flawed and I am not being swayed on that. A dangerous aircraft design found to be even more dangerous - is this Boeing's DC-10?

 

[najaB]

Either way there was no need to have a design of door/plug with only one layer of safety - one set of bolts. That is flawed and I am not being swayed on that. A dangerous aircraft design found to be even more dangerous - is this Boeing's DC-10?

The difference between the DC-10 cargo door design and the 737 exit door plug is that the DC-10 cargo door locking mechanism that failed was exactly that - a mechanism that was operated at least twice per flight. The design of the mechanism was such that it was subject to mis-use, specifically the issue was that, with enough force, the door handle could be moved to the closed position while the actual cams didn't engage with the locking pins. And the people using the mechanism were ground handlers who, no insult intended, weren't highly trained in the minutia of the dozens of types of aircraft they would deal with during a shift and who are under constant pressure to get the job done as quickly as possible in order to avoid flight delays.

The bolts in the 737 door plug are completely passive, and in some cases will never be undone outside of periodic maintenance (I guess the equivalent of a C or D check). These checks aren't subject to the same kind of time pressure, since they typically take days or weeks to complete, and the people performing the checks are trained mechanics who are required to know the detailed specifications of the aircraft their working on.

TL;DR: The two scenarios aren't equivalent.

Edit: Nerd alert - "Boeing's DC-10" is a tautology since Boeing bought McDonnell Douglas!

 

[Bletchleyite]

TL;DR: The two scenarios aren't equivalent.

They are in that it's a flawed, non-fail-safe design. And more generally the 737 Max has seen several accidents through two different flawed elements of its design now.

It's an awful aircraft that should never have flown - a bodge to keep monetising a 1960s design by fitting large high-bypass engines that didn't really fit it and stretching it ad infinitum. Boeing should have done a wholly new narrowbody based on the 787, but they didn't. Perhaps they will now - the reputation of these is in tatters to the point people are actively avoiding flying on them - that hasn't really happened since the DC-10 itself.

Edit: Nerd alert - "Boeing's DC-10" is a tautology since Boeing bought McDonnell Douglas!

I was aware of that - it did seem a bit of a "back to the future" type situation