Is a Boeing 737 MAX the safest plane in service?

Just boarded a 900. Quick visual check from the jetway window looks good to go!

 

I’m on a 900-ER as I type this. So far so good…

 

How's the view?

 

Whilst we discuss the causes, we must not forget how unbelievably lucky ( all of them) they were on this incident.
Had the door failed at 35,000 feet while in cruise speed, several people could have been sucked out of the plane simply because the got up to pick up a jacket or went to pee....not to mention flight attendants, laptops, beverage carts, and so forth
Count your blessings!

 

I'm in my rec room as i type this but I don't know how good it will be. Iv'e got to vent about the 737-900 door failure and i will not refer to it as a "plug door" because it isn't. A plug door is larger than its opening. The peripheral dimensions on the interior side of the opening are greater than the peripheral dimensions on the outer side, necessitating a frame with canted sides, the smaller of which is on the outer edge of the opening. A door designed to close the opening has to be installed inside the airplane and it can only be removed from inside the airplane. It has to fit inside the fuselage frame. Fasteners are designed to keep it in place NOT to retain it under cabin pressure, the PLUG design does that. A 24 X 36 plug door under 10 psi is subjected to a little over 8,000 lbs. of pressure and doesn't need any lugs or bolts to keep it in place. There is no way that it can blow out like the recent panel did. After looking at all of the images that I can dig up, I can see what looks like 5 jugs on each side of the frame of the opening. That's 10 points of failure, plus 10 more for the bolts, plus many more for the fasteners that install the lugs, and I don't know how many points on the panel that blew out. I expect some arrows coming my way.

 

I thought you were saying they reengineered a plug door so that it wouldn't have to open inwards first, which seems to defeat the idea of having a plug door in the first place. I didn't realize they were just making a non-plug door and calling it a plug door to get an easier pass on regulatory requirements.

I'm not an engineer, so I got a bit muddled.

All the best,
Andrew.

 

seat 2A. Everything to the North looked great until it got dark! 41 min to touchdown.

 

Found this picture on reddit of a plug door inspection. Post states it is a not an Alaska Air aircraft

I can see one of the bolts on the floor. Are the top bolts located between the alignment dowels on the left and right side - the 2 sets of 4 rivets?

source: https://www.reddit.com/r/pics/comments/190ih38/boeing_max9_door_being_inspected_right_now_this/
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The most amazing thing about this is that the two iPhones which were sucked out were found, and are perfectly fine!

The door apparently fell in my neighborhood, but I haven't seen it... there is a small lake in the area where the iPhones were found, and I'm guessing the door is at the bottom of the lake.

 

As I see it the area in Red is the only thing keeping the door from sliding up (and out), which allows the blue-circled "stop fittings" (as called in the long video linked on page 3) to clear the "stop pads" effectively locking the door to the frame.
Unless each "stop pad/fitting" has it's own bolt or pin, which can't be determined from this pic.

However with this better picture it now looks like the ~3/16" bolts in the red circle capture pins protruding from the frame, so there are 2 shear planes per bolt. Still should be sufficient, unless someone put a big jack under the door.

Also looks like those could be castle nuts for a cotter pin or safety wire, neighter of which I can make out.

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this shot clearly shows how the bottom hinges allow the door to freely slide upwards, when the bolts above are removed or absent.
Not a super beefy washer under that nut - I can understand how the door was ripped off flapping around in 450mph wind.

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NTSB update just given, made me more concerned about the safety if flying "new/newer" jets than before.
We are getting to confortable during flights and forget things can go bad in a second!
Just a very brief summary of what NTSB reported:
Depressirization ligth came on in 4 previous ocasions on this jet ( Alaska prohibited this particular jet from flying to Hawai !!)
There were several babies onboard, not secured to FAA approved seats
The cabin door "blew open" during the event and hit the bathroom door so hard, it made it stuck
Backrest trays blew open, as well as headrests
One oxigen mask did not dropp
Cockpit crew almost got their headphones ripped from their head

there is more, but sufice to say I am very concerned about the quality and reliability of Boeing's new/newer products....

 

Door has been found.

Crazy that the COCKPIT door blew open.
Also crazy that the cockpit voice recorder only saves the last 2 hours of info, "unless a circuit breaker is pulled".
Maybe not critical in this case, but still at least for training purposes would have been nice to have a record of what the pilots said to each other during the emergency.

Boeing must charge extra for additional SD card memory.... gotta pad that profit margin!

 

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Apparently NTSB is frustrated at FAA for not mandating a 25 hour CVR on all jets, only on new ones....so why dowsnt this have it?

 

Because it is not a new design. A significant portion of the Max is certified to older standards because the particular item is the same or was not a significant change to require compliance with new standards.

 

Which is no different than all the entry doors on the aircraft.

They are two flat mating surfaces, nothing more. Only load reacted, other than any friction load which is not considered, is radial loads due to pressure on the door.

Those bolts carry zero load. The fitting reacts all vertical and inward acting loads on the door. The bolts would only carry load if somehow the stops were disengaged.

Likely a locking nut, which is typical. Dual locking not required for this feature.

The upper fitting would still restrain upward movement. I can't really see enough detail on the lower "hinges" to comment further.

 

I understand this 'vent' is about the doors in general, but the failure occurred on a -9 (Max). The -900 is a NG series.

Had a professor in college who always got ticked off when someone said this, i.e. lbs of pressure.

But the lugs being used on every commercial airliner for the last 60 yrs do keep it in place as well, same as your fabled plug door.

So less than 1000lb per lug. That is a small number. Can you cite any instances of structural failure of these doors (note: this event was not a structural failure).

 

Correct, except if the ~60lb door "bounced" upward which I agree should be nearly neglible force on the bolts.

What "stops" are you referring to?

If you mean the areas in blue below, there's no way they could be disengaged with the red circled part (track or groove on the door side, which allows sliding up and out) unless the bolts are missing or removed.

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Wouldn't it just be more likely that one or more of the bolts wasn't installed or tightened properly? Given this structure is used on a lot of aircraft and in this particular case was setting off cabin pressure warnings.....it seems to be the most likely cause other than a crack in the door frame.

I suppose the door will tell the tale. Pretty helpful that the two cellphones that got sucked out allowed them to track the general area where the door landed.

 

it is a castle nut, with cotter pin
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I can't find a higher res photo than this one, but sure looks like the fixed pin that should engage with the plug/door's "guide fitting" is rather short. Or missing altogether.
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From a newer video about the door plug option specifically:

 

Okay, I said "900" instead of "-9 Max."

 

NTSB video from inside the plane.
~2:00 looks like the big boss taking photos of warped/damaged interior trim on the opposite side of plane from missing door

 

yes, single locking feature

Interesting picture. Based on other designs which use a pin in a socket fitting, the pin is held in place by a bolt to prevent it from sliding in/out of the socket fitting. If the fastener is missing then the pin could slide in and disengage from the fitting on the door.

Also interesting is the guy in the photo with glasses on. Surprised they didn't get sucked out. Although, the cabin pressure is automatically adjusted, and pressurization would not start in earnest until above 8500ft (or there abouts). So door blew out at 16k, thus cabin pressure differential was not anywhere near max of 8.6 psi.

 

United finding loose bolts on raise not doors.
Plus some oter unspecified issues.

is this a qa/qc issue during build or aone sort of design flaw, maybe unaccounted for flex in a longer fuselage.

Either way we’re a long long long way fro if it’s not Boeing I’m not gong, more like if it’s Boeing I’m not going. After so many issues across their line of aircraft seems like they still haven’t gotten it together. Professional finance people and mbas should t be running nuke plants or aircraft manufacturers