Alaska Airlines flight forced to make an emergency landing... 82

[1503-44]

Good to know the door survived.

I have a hard time putting that in the plus column.

The fail light came on December 7 and on January 3 and 4 –- the days leading up to the blowout, she said. Each time, the flight crew flipped a switch to the system’s backup, Homendy said, describing the move as “very normal.”

“They flipped it, they reported it, it was tested by maintenance and then reset.”

What is the "backup" for that? Could be pretty useful for pipelines and pressure vessels. Our operators currently have to hit the "Acknowledge" Button.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[hokie66]

Sounds like the loose panel finally popped out. They should interview passengers who sat beside that panel on previous flights to see if anyone noticed whistling or hissing sounds.

 

[MintJulep]

bolts that needed additional tightening

 

[1503-44]

They probably changed seats. Wouldn't you?

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[3DDave]

About United:

https://theaircurrent.com/feed/disp...s-on-plug-doors-during-737-max-9-inspections/

Check the little b'tard peeking from the back.

 

[1503-44]

After 3 alarms, this "accident" was a sure thing.
Pressure Indicator should normally have a probability of working correctly of around 0.975
1 alarm = 2.5 % chance of the PI being error. (1-0.025) = 0.975 chance of AC malfunction.
2 alarms = 99.93% chance of AC malfunction
3 alarms = 99.998% chance of AC malfunction.
Thems bet the ranch odds.
1 alarm is pretty damn critical from my perspective.
I was on a flight that turned back to the Dominican Republic because the cargo door opened.
Even that wasn't a really great feeling.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[MintJulep]

https://www.flightglobal.com/airfra...37-max-9-door-plug-inspections/156398.article

Boeing issues instructions with details about completing 737 Max 9 door-plug inspections assembly

 

[jrs87]

I suggest cause was missing bolts or missing/wrong threadlock.

 

[jrs87]

Bolts with similar appearance to the ones in United photo.

https://catalogs.shop.boeing.com/Aviall-Product-Catalog-and-Source-Book/4/

 

[jrs87]

Illustration from X (Twitter)

https://twitter.com/NTSB_Newsroom

 

[Roga50]

From the looks of the above diagram plus the picture of the location of the loose bolts found on the United jet, if the bolts fell out of the bottom hinges, that would effectively detach the springs from pushing the plug down into the upper guide fitting.

Without that spring tension, a jolt (like turbulence?) could cause the plug to pop up, clear the upper guide fittings, and open, perhaps?

Here's a picture of one being inspected (posted on Facebook by Uretsky Aviation):

 

[SWComposites]

There is supposed to be 2 bolts in the upper roller guides to also prevent upward movement. They appear to be installed in the photo above.

 

[Murph 9000]

From the looks of the above diagram plus the picture of the location of the loose bolts found on the United jet, if the bolts fell out of the bottom hinges, that would effectively detach the springs from pushing the plug down into the upper guide fitting.

Without that spring tension, a jolt (like turbulence?) could cause the plug to pop up, clear the upper guide fittings, and open, perhaps?

The springs have the opposite function. They push the plug upwards and out of the upper guide fittings; i.e. they assist in opening the plug, by countering its weight and preventing it falling back down into the closed/locked position. The bolts prevent the door from moving upwards, by blocking the movement of the pins in the upper guide fittings and preventing it from sliding upwards on the tubular section of the hinge.

 

[dik]

From the photo of the failed opening. It appears the failure occurred at the upper guide roller. The picture is poor, but it appears the castellated nut and the upper guide track fitting as well as the roller are intact.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Murph 9000]

The guide fitting and nut are not present in that photo, as far as I can see. It appears to be a photo of the open frame, showing only the guide pin. The guide fitting, bolt, and nut are all attached to the plug.

 

[TugboatEng]

I assume the guide rollers are primarily to facilitate alignment of the door until the other 12 fasteners can be installed. If the 12 bolts are missing the stresses may cause the guide rollers to fatigue and fail. This case makes the most sense to me as once the door is in the guides it will appear to be closed so any subsequent steps may be forgotten.

We don't have stringent procedures in maritime but I always tell people to never finger tighten a bolt as it has the appearance of being tightened. If you need to install the bolt and intend to tighten it later always back it off so that it's visibly loose.

 

[Alistair_Heaton]

Your forgetting that the MAX is a 1960's franken creation with no health monitoring capability.

These systems lights come on and the pilots put them in the tech log and the only information the technicians have is what the pilots verbally or written tell them. The 1980's onwards ECAM systems record all system parameters and its relatively easy for them to down load and run through data processors to nail the reason for the light coming on and also a ruff location for the problem. So they know if its a capacity issue or a outflow valve, sensor etc etc. 737 you have a light go hunt the problem down.

We don't get an indication in the cockpit for all of them but basically every single opening in the hull which has a door / valve on it has a status recorded in the HMU (heath management unit) They even record the length of time for the status to change after being triggered.

With these older machines it was a hunt the fault game with certain issues. They were in and out the hanger, fault tested nothing concrete found tested satis on ground sent out again nothing happens for 10 flights closed.. week later same thing again. Until an experience base is built up this sort of thing is hunting a needle in a hay stack.

As for the Cockpit voice recorder, the older machines started recording when the power went on. These days there is some logic of when it records and stops. I think ours is when we turn the beacon on or it senses weight off wheels. Ours are 25 hour units.

But there is shall we say cultural issues. There is an ability to delete it. Some pilots in some cultures delete it after every flight as is their right under national law. They believe that the airline downloads it and uses it. I am not saying that it will have happened this time. More likely after landing because its a 1960's setup it will just keep on running with any power on the aircraft. On the Jetstream we were meant to remember to hunt the circuit breaker down and pull it after an incident. In the USA there very strong opinion on the CVR and what can and can't be done with it.

This situation after the excitement of the incident its understandable why the pilots forgot. The flight safety incident team should have immediately contacted the technicians and instructed them to secure the CVR. I know its on my works incident checklist. And there are technicians on that team that gets formed to coordinate. They have exercises every couple of months to keep current.

 

[MintJulep]

I don't understand the "stop pad" and "stop fittings", but I haven't seen a clear picture of them with a plug installed and closed.

 

[Murph 9000]

I assume the guide rollers are primarily to facilitate alignment of the door until the other 12 fasteners can be installed. If the 12 bolts are missing the stresses may cause the guide rollers to fatigue and fail. This case makes the most sense to me as once the door is in the guides it will appear to be closed so any subsequent steps may be forgotten.

Yes, the guide pins/rollers and corresponding fittings on the plug are primarily to align the plug, not to retain it under pressure. The 12 stop fittings on the plug and stop pads on the frame are permanent structural components. There are no fasteners for them (for opening/closing the plug; obviously there is permanent hardware attaching them to the plug and frame). The plug simply slides downwards to engage them; with the plug in the fully closed position, the stop fittings on the plug transmit the pressure force onto the stop pads on the frame.

Only 4 bolts are involved in normal opening and closing of the plug, two on the guide fittings at the top, and two through the collars which slide over the tubular section extending out of the hinge at the bottom. The bolts are intended to keep the stop fittings and pads aligned.

 

[Murph 9000]

I don't understand the "stop pad" and "stop fittings", but I haven't seen a clear picture of them with a plug installed and closed.

The "stop pads" are the 12 tabs sticking out from the frame. The "stop fittings" are the corresponding 12 tabs sticking out from the plug. It's essentially the same attachment method as a DSLR camera lens, if that helps, just with sliding rather than rotation.