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China Eastern 737-800 MU5735 accident March 2022

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China Eastern 737-800 MU5735 accident March 2022

Old 26th Mar 2022, 15:33
  #221 (permalink)  
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The reliance upon FR24 data as an investigative, diagnostic or even theorizing tool is significantly beyond its design, conception and utility.

While "realistic" results may obtain on occasion, its equivalence to reality is largely stochastic.

The process of building a theory and then going to data to find support is essentially what is occurring through the use of FR24 data. The method is faulty simply because the data isn't good enough to do so. FR24 data is not validated through testing to the same precise standards & legal requirements that DFDR data is. It has its uses, but not in the manner being sought here.

The only tools registered and recognized for such work are the SSCVR & SSFDR, and even then, as we have seen, from such a point there can still be a number of valid theories & interpretations, some ultimately critical to understanding what actually occurred.

If scientists had gone about validating MRNA vaccines in the same manner, we would not be as eager to use them and the FDA would have trouble justifying their wide public use. The principle here and elsewhere in other investigative endeavours is the same.

Respect for the data and for accuracy is paramount as many lives have been affected.

PJ2
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Old 26th Mar 2022, 15:54
  #222 (permalink)  
 
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Longitudinal stability and missing engine

Something very sudden and catastrophic must of happened to go from stable cruise to becoming a barely controllable missile.

an earlier update from searchers said there is no sign of a second engine (having found only one).

At least one part has been found 10 km away.

an engine falling off would definitely cause an upset! What was the maintenance done in the preceding couple days?
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Old 26th Mar 2022, 16:44
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MLHeliwrench

If you refer with your #215 to my #193 update on the search ? ... I have to say that it mixes official statements, statements of the reporter on-site (who do seems to talk to the investigators and police that are present on site), and my own observations based on the photos and videos that I found.

Your ... "So when an earlier update from searchers said there is no sign of a second engine (having found only one)."
In my post that means that I have only seen one engine (100% sure, seems complete but with hi spd impact flattening). As far as I know, pity I dont speak Chinese, there have not been any official statements on the engines, or the four corners for that matter.

Your ... "At least one part has been found 10 km away."
Officials reported that a1.3m x 10cm wide piece was found by a farmer in his field. Up till now I have not heard any confirmation that it actually belonged to a plane or the plane. A bit odd that it takes so long.

There is a big piece reported to be part of the THS (I have a photo that seems to be the one they mean, still have to check that), both by the reporters and repeated by officials. No reports on elevators.

There was a report on a big piece that was found yesterday morning, the reporter said they thought it was the tail, but at the end of the day it was still sitting there and not completely dug out. Very hard to get heavy pieces from there. The winglet and part of the outer wing was removed by using a kind of bamboo sled on a bamboo road. After they had moved it, the bamboo road was unuseable.

So, very important information that can reduce the number of possible scenario's is still missing.

There is one remaining row of blue tents were all the parts are collected, cleaned and sorted. The other row has been removed to make way for the excavators. They now have so many fragments (I can't call them parts) that they are going to create a special area in the next few days for the processed ones. Another next step is taking the 'mud' (it was still raining) and filtering that in two stages to try to filter out everything. The 'gulley' is now being dug out both North to South and sideways. As officially stated the main impact area had a radius of 30m and a depth of 20m. With rain starting about 2 days after the crash but continuing, makes it a heck of a job, they are now removing part of the bamboo forest, working even harder on drainage, etcetera.

So a lot of hard work still going on.

The engine scenario is an interesting one. People will say unlikely, but would be interesting to factor in asymmetry and loss of thrust.

Last edited by A0283; 26th Mar 2022 at 17:14.
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Old 26th Mar 2022, 17:20
  #224 (permalink)  
 
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Originally Posted by Sailvi767 View Post
Why would they not simply disconnect the trim or just grab the trim wheels? Both those fixes assume the system that automatically shuts down a runaway trim if the control column moves opposite the trim direction has failed. A runaway trim at cruise altitude should be a non event.
Well, we got shouted down asking that question of the two MAX accidents as it somehow implied the pilots hadn't done their job properly and was taking some of the heat off the anti Boeing witchunt that was the only politically acceptable cause in town..
What's different here?
But of course you're right, with a runaway trim you do the drills and circumvent it. Easily.
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Old 26th Mar 2022, 17:52
  #225 (permalink)  
 
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From official reports: "Rescuers have found the emergency locator transmitter (ELT) installed near the second black box <the FDR> of the crashed plane. .. Search in the main impact area … More orange pieces were found at the core search area that experts later verified are parts of the black box."

Next to that, a photo shows that a 3D model of the impact site is being prepared. There is no information on either a photogrammetry or LIDAR basis. But I think this will certainly become a standard tool in the accident investigation toolbox. Especially useful in remote and uncharted locations like these.
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Old 26th Mar 2022, 19:02
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Originally Posted by fdr View Post
Nor do I;

reading the follow on posts, here is some physics for pondering for the other posts....

Planes fly nicely unless they are either -
  1. commanded to do something else; or
  2. upset by external factors; or
  3. the fundamental stability of the toy gets upset.
A plane that is happily bumbling along at 1.0g doesn't suddenly decide to go to 0.3g. the trim solution is to an angle of attack, and it is not going to have a large excursion from that to some other value just because the autopilot decided to turn off. If the autopilot elected to enter a wild ride, then as long as the autotrim function is running the plane will happily retrim to the new angle of attack and do what the errant autopilot computer is commanding. The plane continues otherwise doing its short period or long period oscillations around the mean trim alpha. Yaay. has been like that since Wilbur and Orville decided that the world needed flight attendants to make it a more palatable life.

A pilot pushing on the prong will drop the nose, as long as he (or she, but most she's are not stupid enough to do what the boys do) is pushing. As soon as he (or she) lets go of the input, the plane is going to revert to the trimmed alpha, and it will do a recovery all on its lonesome. Not just nice to have, it is a mandatory design requirement, even for unstable designs, the 1's and 0's have to be able to guarantee that is always the case.

getting to a seriously nose low condition takes a lateral excursion in order to occur unless the tail has gone its own way, and as was previously mentioned, with Lauda 004, "Mozart?" when the inadvertent thrust occurred on an engine in the mid climb, the PW4060 issue resulted in a huge disruption of the flow over the wing section immediately behind the nacelle, and that caused a large lift loss as well as yaw. As the aircraft rolled from the loss of lift, and from the secondary effect of the yaw, eventually the structure got to a point of exceeding the strength of the tail and the tail failed, by memeory with an asymmetric failure of the horizontal stab/elevator and then complete failure of the vertical stab, whatever, shortly thereafter, from the loss of the horizontal stab, the Cm from the wing and the CG shift of losing a stack of weight at the tail resulted in a rapid pitch down, that ended up with an overload of the main wing from an excessive negative g loading, after which the wings departed, and what was left was not much at all. A full on failure of the tail usually ends with the sky filled with chaff, an inflight breakup is almost always the outcome. JAL103 was an exception to that.

An aircraft that has a lateral upset is the most common means of getting into a nose low attitude. This can be from curious causes, Silkair being one, or the Classic loss out of Jakarta last year with the autothrottle clutch pack issue, or from entry into turbulence, or from instrument failures, like Stansteds B747-200F loss, or Adam Air with the INS's attitude being reset in IMC... that'll do it every time. When the aircraft rolls to a high bank level or inverted, the longitudinal stability will tend to drop the nose as the plane enters a spiral at high bank angles or tries to do a split S if inverted. The planes stab trim doesnt need to be altered and the outcome is a degrading flight path. What doesn't happen is the plane going to 0.3 g or other, it is trying to get back to the trimmed alpha, and that means it will tighten at the high bank angles, so g loadings increase. Tracking data if it is reasonably high resolution may show that a track change has occurred, but getting the nose down without changing the trim needs the roll.

On the morning of this accident, I was planning a medevac into China for the following day, and the plane involved had a recent radar issue that had resulted in a radar swap. As part of the planning, I looked at the weather in southern and eastern China, about 4 hrs before the accident and there was convective weather forecast near Guangzhou and to the west, and otherwise the area was quite clear. tops above FL260 were not significant except in that area, and the lightning strikes were being displayed in that area, then next closest area was over Pusan/Pohang and south of Vladivostok.

The grounding of 200 plus B738s seems to be premature. Unless there is clear evidence of a stab tab or other item falling off around the top of the drop, there is not much likelihood int his case that a structural failure was involved. Parts that separated part way down were unlikely to be the cause, they are the consequence.

Having said all of that, occasionally stuff really is surprising. I recall one investigation where the crew got 12,500FPM upwards, busted the assigned altitude by 4000' topped out at 0.2g, and then got 12000FPM on the down side and busted the assigned altitude a second time for good measure. The pull up was 1.3g, the over the top was 0.2, and the pull out was 1.3g. That got a spot on the wall, for the rest of the day until the next incident surpassed it. During the rollercoaster, the Captain managed to complete the full multi language PA to the passengers welcoming them on board and thanking them for choosing to fly brand X. The FO has the misfortune to be in a spritely climb in a light plane and to encounter an entry into a jetstream that increased the headwind by well over 100kts over 4000' and he elected to stay in FCLH targetting Mach.... so the latter climb was all done with the thrust levers at idle, and one very confused FO. The cabin crew continued their excellent, long suffering service, and didn't leave any dents in the ceiling.

TBs maths is OK for a wings level entry, using a dFPV/dt, V input, to determine a g loading, but anything that achieves that in a wings level condition is a seriously catastrophic event, the fact that the aircraft had any reduction in the severity of the dive angle suggests it was still responsive to control un until the time it then wasn't. 73 drivers don't often do push overs, recall that they drivers are sitting a fair arm forward of the CG, and the rate of pitch needed to go to zero g gets the drivers up close and personal with the fuel panel and the pressurisation control panel unless well strapped in.

Pushing to zero g and holding it for any time is a good push on the prong, gonna get tired doing that for long, and to hold it, without running the stab trim, that is a big ask


Thank you that is very informative
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Old 26th Mar 2022, 21:39
  #227 (permalink)  
 
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'Your ... "At least one part has been found 10 km away."
Officials reported that a1.3m x 10cm wide piece was found by a farmer in his field. Up till now I have not heard any confirmation that it actually belonged to a plane or the plane. A bit odd that it takes so long.'

Maybe not confirmed, but it was reported in the presser about 12 hours ago that they have dispatched four full search teams in that direction for 10 kms away from main crash site.

What a massive and terrible task .. highest respect for them all.

Last edited by T28B; 27th Mar 2022 at 15:08. Reason: Neon green is an awful color
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Old 26th Mar 2022, 23:59
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Bloomberg reporting:China said it hasn’t found any evidence of explosive materials in the wreckage of a China Eastern Airlines flight that crashed with 132 people on board.

“Lab tests taken of 66 samples, 41 of which have been completed, showed no major common inorganic explosive or common organic explosive substances have been found,” fire official Zheng Xi said at a briefing in the southern city of Wuzhou on Saturday.

Zhu Tao, an official with the Civil Aviation Administration of China, added that investigators found a transmitter installed close to a missing black box that records flight data, but haven’t retrieved the device itself. A black box that captures voices in the cockpit was found earlier.

Some 24,000 pieces of wreckage have been retrieved, officials said, and remains of 120 people have been identified. The search is focused on an area with a radius of 300 meters (about 330 yards) from the main crash site, though part of a wingtip was found 12 kilometers away.

More at link .. https://www.bloomberg.com/news/artic...d=premium-asia
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Old 27th Mar 2022, 00:30
  #229 (permalink)  
 
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If a wing tip was found 12 kms away, imho this very case has some similarities with both Ceiba 738 and GOL 738 (both coliding with exce/biz jets) but however with different outcomes...in GOL case survived the Bizjet, in CEIBA survived the 738.
Could it be the case and being China such a military country they had some midair colision with an UAV, Drone, mil device, etc?
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Old 27th Mar 2022, 00:54
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Originally Posted by meleagertoo View Post
Well, we got shouted down asking that question of the two MAX accidents as it somehow implied the pilots hadn't done their job properly and was taking some of the heat off the anti Boeing witchunt that was the only politically acceptable cause in town..
What's different here?
But of course you're right, with a runaway trim you do the drills and circumvent it. Easily.
Forgive my ignorance, but I thought that there were regimes where runaway nose down trim causes the autopilot to say "it's yours" and given the resultant high speed dive, it can be nearly impossible to manually dial back the trim wheel without resorting to a phugoid yo-yo maneuver.
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Old 27th Mar 2022, 00:56
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Originally Posted by Jason74 View Post
Credentials:
15 years Royal Australian Air Force. Qualified on PC9, C-130, Macchi MB-326, F/A-18, Hawk-127. Qualified Flying Instructor, Instrument Rating Examiner, Low Level Demonstration Pilot, Flying Safety Officer.
15 years airline pilot. Captain on A350, A330.

Causative Factors:
Absolutely no idea. How could I offer an opinion before the data is in?


My deepest condolences to the families of those involved.
Lol, saved me the effort. Well said, indeed cleverly , and aimed at the man on the high horse.

I like to hear what the "amateurs" say.
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Old 27th Mar 2022, 01:59
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Originally Posted by Sailvi767 View Post
The trim system in the 737 is very obvious if not annoying when running. That includes when the autopilot trims. If in fact they ignored the spinning trim wheels and noise as soon as the autopilot moved the elevator to counter the incorrect trim input the trim brake would engage and stop the runaway.
Does not the 737 AP trim via moving the stabilizer, not the elevator?
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Old 27th Mar 2022, 03:13
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FDR recovered.

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Old 27th Mar 2022, 04:13
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screen grab of 2nd black box from CGTN live broadcat ...


Last edited by sopwithnz; 27th Mar 2022 at 04:42.
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Old 27th Mar 2022, 05:09
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Originally Posted by cncpc View Post
Lol, saved me the effort. Well said, indeed cleverly , and aimed at the man on the high horse.

I like to hear what the "amateurs" say.
Tend to agree especially if someone states this is the reason. Maybe I missed that but most appear to have indicated along the lines of this "may have happened".
.
In respect to offering an opinion, "Causative Factors:
Absolutely no idea. How could I offer an opinion before the data is in?.

An opinion is "a view or judgement formed about something not necessarily based on fact or knowledge". So by all means offer your opinion and if outside the bounds of reasonability standby to receive.
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Old 27th Mar 2022, 06:01
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Originally Posted by Mudman View Post
10km radius around the crash site.

10km radius around crash site
According to SCMP News article the farmer who found the piece lives at Yatang which is SW of Tangbuzhen on a hill. On the image above it is where the red line crosses that industrial complex to the right of the Yandong town label next to the river.
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Old 27th Mar 2022, 08:16
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Well, the 737 series did have a problem in the early 1990s that caused several hard-over events (and two crashes). Jamming of a valve in the rudder hydraulic power unit.

However, to the original question, that was fixed with a new part design, and there have been no recurrences in 26 years. So no reason at all to think it especially probable in a 737 built in this century.
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Old 27th Mar 2022, 10:36
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Press Conference an hour ago ...

reporting more wreckage has been found today 8 kms away from main site ...
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Old 27th Mar 2022, 12:09
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Originally Posted by theFirstDave View Post
Does not the 737 AP trim via moving the stabilizer, not the elevator?
You are correct.
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Old 27th Mar 2022, 12:13
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Originally Posted by meleagertoo View Post
Well, we got shouted down asking that question of the two MAX accidents as it somehow implied the pilots hadn't done their job properly and was taking some of the heat off the anti Boeing witchunt that was the only politically acceptable cause in town..
What's different here?
But of course you're right, with a runaway trim you do the drills and circumvent it. Easily.
Because MCAS on the Max does not act quite like a normal runaway trim and defeats the trim brake.
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