China Eastern 737 Crash: What Caused the Unusual Cruise Phase Tragedy?

[russ_watters]

TL;DR Summary

Discussion of the China Eastern 737 crash on Monday, 3/21.

On Monday, 3/21 a China Eastern Airlines 737-800 crashed, killing 132 people.

What is unusual about this crash is that it happened from the cruise phase of flight. This is usually the safest phase, as the plane is flying straight and level most of the time and nothing is changing so there shouldn't be anything happening to trigger a problem, and there is more energy/time available to deal with problems that might occur. Contrast that with takeoff and landing, when time and energy are limited.

Video shows what appears to be an intact plane pointing straight down as it fell:
https://nypost.com/2022/03/21/the-moment-china-eastern-boeing-737-nosedives-before-fiery-crash/

This indicates it had a brief recovery but otherwise dropped rapidly, at up to 30,000 fpm (300 kts) and during its recovery reached maybe 575 kts (above its cruising speed):
https://www.flightradar24.com/blog/china-eastern-airlines-flight-5735-crashes-en-route-to-guangzhou/

Note that the speeds are ground speeds not airspeeds, indicating it flew very fast but also not straight down for much of the descent.

There are only a few scenarios that we've seen for crashes from high altitude and this would seem to preclude most:

• Riding a stall to the ground at low speed (Air France 447)
• Explosive decompression, causing in-flight breakup (multiple)

I can only think of two scenarios that might look like this:

• Runaway trim (though note, this was not a 737 Max)
• Intentional (terrorism/suicide, such as United 93, Germanwings 9525)

 

[DaveC426913]

I depart in 48 hours. Thanks Russ.

 

[anorlunda]

The videos seem to eliminate the possibility of in-flight breakup.

Speculation without the final report won't expose an intentional act. The hope here is that the flight recorders are recovered intact enough to tell us what happened.

In past cases, speculation that the pilot (pilots?) committed suicide was highly traumatic to the pilot's family, but in some cases some other cause was the final conclusion. IMO, public speculation about deliberate acts without evidence is harmful and should be discouraged.

 

[fresh_42]

IMO, public speculation about deliberate acts without evidence is harmful and should be discouraged.

Honorable. However, the B737 is a workhorse for decades. Mid-flight almost rules out a maintenance problem, an intact plane rules out a bomb or other causes for physical breaks. The fire rules out a fuel problem. The stall almost rules out a steering or trim problem.

There is not much left for reasonable causes.

 

[Klystron]

There is not much left for reasonable causes.

For the record without speculation concerning this flight, other factors affecting flight safety,

• atmospheric conditions including shear, lightning, severe turbulence.
• FOD foreign object damage, natural and human caused including weapons.
• human factors not previously mentioned such as over/under reaction to emergencies.
• catastrophic equipment failure including electrical, fuel system, engines, trim system...

This thread alerted me to this event. B-737 a stable reliable transport within envelope.

 

[russ_watters]

For the record without speculation concerning this flight, other factors affecting flight safety,

• human factors not previously mentioned such as over/under reaction to emergencies.

This made me think of another:

• Crew incapacitation (several examples)

This has happened several times due to slow depressurization. It usually happens while in autopilot and the crash generally occurs after running out of fuel. It would be possible if the plane was being flown manually, as well as a brief attempt to regain control before the final crash.

 

[anorlunda]

The stall almost rules out a steering or trim problem.

What stall? The data I saw gives no hint of a stall. The data shows a dive with almost zero change in heading. A stalled plane rotates like a falling leaf.

 

[fresh_42]

What stall? The data I saw gives no hint of a stall. The data shows a dive with almost zero change in heading. A stalled plane rotates like a falling leaf.

That's what I meant. An airplane with things like shifted cargo, lost flight control, structural damage, or even stalled engines won't fall like a rock. They stagger.

 

[russ_watters]

That's what I meant. An airplane with things like shifted cargo, lost flight control, structural damage, or even stalled engines won't fall like a rock. They stagger.

It also looks to me like you misspoke. Did you mean to say *lack of a* stall?

 

[fresh_42]

It also looks to me like you misspoke. Did you mean to say *lack of a* stall?

I thought "stall" would describe any case without an aerodynamic lift.

 

[DaveC426913]

an intact plane rules out a bomb or other causes for physical breaks.

Do we know the whole plane is intact? Or do we only know the fuselage is intact from the photos?
What if a wing (or two) came off?

 

[russ_watters]

I thought "stall" would describe any case without an aerodynamic lift.

No, it's a specific condition where you have a flow separation over the top surface due to too high of an angle of attack. Diving toward Earth and having the wing produce no lift because zero effective angle of attack is not a stall. A plan in a fully developed stall is falling like a leaf, relatively slowly.

A stall can still produce a situation where the plane dives to Earth though, since the nose will drop in the effort to build speed and recover. This happened for AF447 right before hitting the water, whereas most of the descent was in a fully developed stall.

Difference being that if you are in a dive you can just pull up out of it. If you are in a stall you have to nose down to build up speed first.

 

[berkeman]

What stall? The data I saw gives no hint of a stall.

Well (I know this is problematic without a reference), when I first heard the radio report of the crash, the commentator (CBS? NBC?) said that there was evidence that the plane pitched up before stalling and going into that nosedive. But I haven't seen anything about that since, so perhaps I misunderstood or the commentator was talking out their APU...

 

[anorlunda]

said that there was evidence that the plane pitched up before stalling and going into that nosedive.

Here's the data I saw at

Above, we see heading

yellow is ground speed (not airspeed) In a vertical dive, ground speed is zero.

blue is altitude

The commentary notes that the dive started very close to the point where the flight
plan would call for beginning descent to the airport.

 

[russ_watters]

Do we know the whole plane is intact? Or do we only know the fuselage is intact from the photos?
What if a wing (or two) came off?

It's unlikely that a wing or two could come off without the entire plane breaking-up or even exploding. It's possible part of the tail could have come off without it being visible in the grainy video I linked.

There was one I vaguely remember where part came off but it mostly remained intact while it nosed-over into the ground. I can't remember if it was the nose or tail though...

 

[DaveC426913]

Ah crap. Our flight on Thursday is aboard a 737-800.
https://flightaware.com/live/flight/SWG342

 

[berkeman]

Ah crap. Our flight on Thursday is aboard a 737-800.
https://flightaware.com/live/flight/SWG342

I think they are all grounded in China now, no? Besides, what are the odds?!

 

[berkeman]

Wait, you're flying to Cuba?

 

[DaveC426913]

Yes. Don't rob me.

 

[DaveC426913]

I think they are all grounded in China now, no? Besides, what are the odds?!

Heh. Yeah. If this particular plane falls out of the sky and kills me, I'm going to start buying lottery tickets.

 

[fresh_42]

Wait, you're flying to Cuba?

View attachment 298779

Don't be jealous. We others are allowed to.

 

[Oldman too]

From the NYPost article.

It is very likely that the aircraft lost power at cruising altitude, resulting in the pilot losing control of the aircraft,” Wang Ya’nan, chief editor of Beijing-based Aerospace Knowledge, told China’s Global Times. “This is a very serious technical failure in which the plane inevitably enters a high-speed descent.”

 

[berkeman]

From the NYPost article.

It is very likely that the aircraft lost power at cruising altitude, resulting in the pilot losing control of the aircraft,” Wang Ya’nan, chief editor of Beijing-based Aerospace Knowledge, told China’s Global Times. “This is a very serious technical failure in which the plane inevitably enters a high-speed descent.”

I call BS. As others have said, losing power at altitude is not that difficult to deal with. Something else happened.

Could you post the direct link to the story please? Thanks.

 

[Oldman too]

I call BS. As others have said, losing power at altitude is not that difficult to deal with. Something else happened.

Could you post the direct link to the story please? Thanks.

https://nypost.com/2022/03/21/the-moment-china-eastern-boeing-737-nosedives-before-fiery-crash/

About the quote I posted, (Wang Ya’nan, chief editor of Beijing-based Aerospace Knowledge) We should consider the source.

 

[fresh_42]

As others have said, losing power at altitude is not that difficult to deal with.

A pilot once told me: There is no problem as long as you are high enough. There has been enough height, and those machines tend to stabilize themselves again. You don't even have to interfere if there is enough time. So even without fuel, which could hardly have been the case due to the fire we saw, the aircraft can still operate as a glider at lower altitudes.

 

[berkeman]

https://nypost.com/2022/03/21/the-moment-china-eastern-boeing-737-nosedives-before-fiery-crash/

About the quote I posted, (Wang Ya’nan, chief editor of Beijing-based Aerospace Knowledge) We should consider the source.

Thanks for the link. I still call BS (on him, not on you). This senior editor is obviously not a pilot. (of course, neither am I, but I know how my paper airplanes behave when they "lose power"...)

 

[Oldman too]

A pilot once told me: There is no problem as long as you are high enough. There has been enough height, and those machines tend to stabilize themselves again. You don't even have to interfere if there is enough time. So even without fuel, which could hardly have been the case due to the fire we saw, the aircraft can still operate as a glider at lower altitudes.

True, see; https://www.gimliglider.org/

 

[fresh_42]

I have to correct the quotation. He actually said: There is no problem as long as you are high enough except fire.

 

[Oldman too]

Thanks for the link. I still call BS (on him, not on you). This senior editor is obviously not a pilot. (of course, neither am I, but I know how my paper airplanes behave when they "lose power"...)

I've never seen or heard of an example where an aircraft flies straight down like the one in that image, what would it take to hold the aircraft in that attitude for an extended nose dive?

 

[fresh_42]

I've never seen or heard of an example where an aircraft flies straight down like the one in that image, what would it take to hold the aircraft in that attitude for an extended nose dive?

That's a good question. A B-737 is not an aerobatic machine that can perform all kinds of maneuvers. E.g. the extended suicide mentioned above was done by programming the autopilot to a height below the height of surrounding mountains. The determined crash actually took a while, and stuff, as well as passengers, knew it. I assume that such a nosedive is extremely difficult to get in, especially as you can no longer sit and fly.

 

[Baluncore]

This is certainly a peculiar event. If the vertical stabiliser was lost it would have tended to flat spin, which it did not. I could not see the wings in the surveillance video, so either the wings were missing beyond the engines, or roll attitude was under control. Without voice communication notifying an emergency, the obvious explanation of murder-suicide by pilot is possible. In this situation, any evidence of a midair breakup will be on the ground, not lost at sea. We must wait for the results of the investigation before reading the certain explanation.

 

[berkeman]

I've never seen or heard of an example where an aircraft flies straight down like the one in that image, what would it take to hold the aircraft in that attitude for an extended nose dive?

The video that @anorlunda posted addresses that. It seems to take a non-passive forced nose down attitude from a mechanical failure or a persistent cockpit input.

Here's the data I saw at
View attachment 298775
The commentary notes that the dive started very close to the point where the flight
plan would call for beginning descent to the airport.

 

[Oldman too]

That's a good question. A B-737 is not an aerobatic machine that can perform all kinds of maneuvers. E.g. the extended suicide mentioned above was done by programming the autopilot to a height below the height of surrounding mountains. The determined crash actually took a while, and stuff, as well as passengers, knew it. I assume that such a nosedive is extremely difficult to get in, especially as you can no longer sit and fly.

I'm not a pilot, however I've spent years on MS Flight Simulator, a very good physics model with a good variety of aircraft. Not that I'm suicidal or anything but I've tried to perform that exact same maneuver as described in the article (and image) It's way beyond my ability no matter what plane, weather conditions etc. I have to admit I'm baffled.

 

[anorlunda]

The glide ratio of a 737 with no power is on the order of 17:1. Starting from 29000 feet, down to 3000 foot mountains, it could glide about 130 km. Air Transat 236 (Airbus 330) ran out of fuel mid-Atlantic. It glided 121 km to the Azores and landed safely. https://en.wikipedia.org/wiki/Air_Transat_Flight_236

For the sake of the pilot's families, please don't speculate publicly about suicide. You can believe it privately, but don't be so cruel as to post it on a forum that is indexed by Google.

Hijacking is another explanation for a deliberate descent.

 

[russ_watters]

Thanks for the link. I still call BS (on him, not on you). This senior editor is obviously not a pilot. (of course, neither am I, but I know how my paper airplanes behave when they "lose power"...)

@Oldman too

Sorry guys, that's my source. I picked it because it had the video link and didn't read the article. Yes, it's clearly BS. Perhaps an opening argument/pre-emptive strike against Boeing?