As a general question, how reliable is Chinese accident investigation and reporting?

It was reportedly CCTV footage from a nearby mining operation playing on TV, filmed on a mobile by someone.

The thing is, the speed is constant until the descent starts. If altitude was maintained after an engine failure, there should be a decrease in speed.

While ~31,000 fpm is a decent velocity, I think we are talking about descent rate.

Of all the places, I'd have thought folks here would have known what they were talking about :ugh:

I wouldn't even call it a descent rate. It was a terminal dive. I wonder what the engines were doing ?

https://cimg7.ibsrv.net/gimg/pprune....264cde4a84.jpg
MU-5735 descent video still

https://cimg4.ibsrv.net/gimg/pprune....a6be94045e.jpg
Wider view of wing structure MU-5735

The video from this still is real. The guy in the video speaks Cantonese with a really heavy accent and the two words I understood was "直落" which means "straight down." There are two provinces in the whole of China (besides HK and Macau) where locals speak Cantonese.. Guangxi (where the plane went down) and Guangdong.

Too many armchair experts in this thread :ugh:

With the two MAX disasters being so recent, any B737 pilot should have been fully up to speed on dealing with stab trim malfunctions. Surely this would have been highlighted by the training departments of all B737 operators, with a relevant exercise being included in the required training or testing sessions.

As the aircraft was a passenger varient, a massive CofG shift due to unrestrained cargo seems unlikely.

An Alaska Airlines flight 261 scenario with the stabilizer commanding full down pitch due to mechanical failure or improper maintenance would be one of the first possibilities to look into. Perhaps an issue similar to the rudder hard overs experienced back in the 1990s has reared its head.

Pilot suicide or unlawful interference are possible as well.

Jet Upset
 

A “ Jet upset “ is a strong possibility.

Any distraction to the flying of the plane or a control problem at altitude can become a crash.

As the aircraft approaches high Mach speed the lift moves back, due to Mach effects. The nose lowers more and only in lower thicker air does the elevator have sufficient control authority.

Most modern airplanes have a Mach Trim, which will apply nose up stabiliser to help control this effect.

The issue is, if the plane’s speed is not controlled adequately early on in the descent, then the airspeed loads or manoeuvring loads in the lower thicker air can destroy the airframe.

See Wiki for “ Jet Upset “ and also “ China Airlines 006 Feb 1985 “.

The 747 tail plane has chunks missing from the near supersonic descent. It’s incredible it survived.

( Apparently part of the reason the 747 survived is that some of the gear fell down, breaking the up locks as it was pulling 5 g, the extra drag helped to limit the airspeed.)

So this aircraft ended up going very fast with bits falling off it.

Loss of control at altitude due to Mach effects can lead to rapid airspeed build up and excessive air loads in lower thicker air.

This 737 unfortunately seems to have had a very rapid descent, for whatever reason leading to inflight breakup.

A lot of folks seem to take it as a fact that the aircraft was temporarily recovered, briefly climbing, just before crashing - according to the tracking site. Watching the videos, if they are accurate, this seems highly unlikely though.

Remember, the altitude data from ADS-B / FR24 site is a barometric pressure reading transmitted by the aircraft itself only. Sure, in normal flight, a reduction in barometric pressure correlates with a gain in altitude. But when an aircraft left controlled flight, there are other reasons which could cause a temporary reduction in barometric pressure at the static port - which would falsely be interpreted as a brief climb.

So, what you should take as a fact is: we don't know...

Industry rumours there may had been significantly in excess of a dozen deadheading flight crew on-board.

-- x --

Unlawful interference by overpowering the flight controls by a 3rd party is rather beyond imaginable, given the physical and procedural barriers. Mainline Chinese carriers employ uniformed security guards and cockpit access procedures are strict 100% post-9/11.

-- x --

Was there really a climb segment before the impact? If so, one speculative chain of events:
- upset + loss of control / spatial disorientation at high alt
- high speed dive with severely abnormal attitude in IMC
- break cloud with crew regaining orientation but overstressing the airframe during a belated attempt to avoid crashing which was impossible to pull (no pun).
- partial physical brake-up of aerodynamic surfaces due to overload, namely some of the tail structure
- dismembered hull plunges to the ground.

As clueless as anyone. Is the countrywide grounding of 737-800 by CAAC confirmed?

Credentials:
30 years plus on Boeings, 20 years plus as wide body Captain.

Not being one to speculate but maybe they lost an engine and instead of drifting down stalled the aircraft, then put in the wrong rudder or tried to use aileron to recover the dropped wing then ended up inverted in an energy and attitude state that was beyond their capability to recover from.

But I guess we will only know when the CCP release their transparent report into the incident.

My condolences to all on board.

If we are to believe the FR24 data, it does not logically back up a trim runaway scenario. The speed (I'm still unsure whether we are talking G/S or TAS), drops slightly just before descent. This would not be abnormal if this was TOD as the aircraft sequences to ECON descent speeds (Mach). But then at about the time the descent rate increases exponentially, the speed is shown as a good 70-90Kts less than Cruise/TOD schedule. This anomaly lends itself to some other form of event unless the data table has a high inaccuracy capability. Only the CVR/FDR will allow those that analyze these events the opportunity to piece together the possible causes, hopefully arriving on a conclusive reason.

You understand that yoke trim switches have an "power button" button and a "direction" button? It's unlikely both switches would fail. Also, faulty yoke switch inputs can be immediately overridden by pulling/pushing on the stick in the opposite direction, then the cutout switches can be used.

Avionics maintenance engineer (40 years)

Any thoughts on how likely serviceability of the recorders will be. Looks like nothing left of the aircraft. Know they are tough, but not indestructible and there was a big fire.

Credentials: Retired military and airline pilot

Working backwards, it appears we have a near vertical dive with some associated breakup. How do we arrive in that position? Imo:
1. Catastrophic mechanical failure in cruise - unlikely
2. Pilot suicide - unlikely, plausible.
3. Terrorist act - unlikely, plausible
4. Gradual stab trim until autopilot gives up and kicks off, followed by departure from controlled flight. Recovery attempt overstresses aircraft. - plausible
5. There are many other ways to depart the aircraft and botch the recovery. - all plausible at this point.
We are going to have to wait and see.

The recorders will almost certainly not be serviceable, i. e. they will be destroyed and will not work.

But the memory modules will almost certainly still be readable; they are in some of the toughest enclosures you can imagine, they can protect the memory from shock in excess of 1000 G acceleration, and prolonged hot fires. It is the enclosures' only job to protect the memory modules in precisely this kind of situation. This looks like a head-on crash with a velocity not too different from the Germanwings murder-suicide, so the entire aircraft acts as a crumple-zone reducing the acceleration experienced by the recorders.

The problem will be to find them. This can take weeks.

As a long time 737 captain I would say that a 737 loss from at or near cruise altitude is quite an unusual event. But it does remind me of at least one Indonesian loss of control accident (Adam Air?). Flight level 290 is not that high and the chance of being in instrument flight conditions cannot be excluded. Very few airlines encourage manual flight that high and if the airplane departed controlled flight for some reason then the startled crew might not perform a text book recovery. There is some data suggesting the aircraft made a high speed pull out relatively low with the possibility of over stress and ensuing breakup. But that is just speculation. It is a bit of a short flight for fuel imbalance to be a big issue. But technical failure, plain and simple operator error or of course some exterior factor like turbulence could have caused the initial loss of control. The black boxes will hopefully show up shortly and then we will have something firmer to go on.

lederhosen thanks! One of the reasons behind crew losing themselves at the onset (not saying it actually happened) could be a simple but deep confusion.

I recall a guided training SIM session on the Classic with Dual Eng Fail at TOC design to experience exactly that. For the NG, would the resulting electrical configuration & systems remaining be a lot to handle? Startle effect included.

For the sake of exploring the technological consequences of such a scenario.

-- x --

links to some cases already mentioned (varied relevance)

1997 Silk Air 185: Unconfirmed deliberate CFIT
https://aviation-safety.net/database...?id=19971219-0

2007 Adam Air 574: Spatial disorientation
https://aviation-safety.net/database...?id=20070101-0

2015 Germanwings: Pilot suicide
https://aviation-safety.net/database...?id=20190223-0

2019 Atlas Air: Upset due undesired TOGA activation
https://aviation-safety.net/database...?id=20190223-0

Lets not get sanctimonious on our reporting and safety...after all it was the chinese who first grounded the Max.... and if not for them I would bet the FAA wouldn't have, and instead did some sort of software workaround and leave no sensor redundancy on the MCAS.

If it was a collision with military equipment the publishing part will be challenging and not necessarily overcome without a cover story. But no doubt the reason will be found out and corrective actions taken.

One of the power-pillars of a controlling government, anywhere, is providing (a sense of) security to its own people. Falling aeroplanes are cross with the marketed purpose.

On top of that, as W.C.'s far eastern twin would have said: "Never let a good uproar go to pass without public punishment."

No, logic tells us that we don't know yet WHAT happened.

Firewalling the thrust levers from stable cruise will have a marked pitch-up but nowhere near what's required to cause an upset. At FL290 the engines operate near maximum available thrust for thermodynamic and engineering efficiency anyway.

The second part, overzealous pushover and nosedive, might be similar. But the trigger needs to be a different one.

As well, noted by wiggy earlier, the geometry of TLs in their forward cruise position places the TO/GA buttons out of the way, not to mention those are completely different designs between 767 and 737. Or someone reaching for the flap lever at that altitude...

I linked the accident report only for completeness, the dynamics look uncorrelated IMHO.

[in reply to a questions about Chinese accident investigation quality]

I agree. Also keep in mind that under ICAO rules they are required to allow representatives from the country of aircraft design (USA) and aircraft manufacturer (also USA) to participate in the investigation:

They won't have a say in the report, but will be allowed to observe, and can write their own additional, if unofficial, reports.

Traditionally, the engine design and manufacturing companies also request and receive permission to send representatives, but there is no such obligation under ICAO Annex 13.

The angle of the video relative to the flight path could make it seem like it was going straight down.

If the video was taken perpendicular to the flight path, then that would be correct.

If it was taken parallel to the flight path, it might not have been able to pick up a horizontal component of the plane going away from the video camera.

Either way, it shows a high rate of descent.

I’ll leave it to others to map out where the camera was relative to the flight path and won’t post again on this thread.

I have not seen anything relating to ATC chatter anywhere. I have no experience with Chinese ATC. Is it something that we are likely to see released, or will it fall into the CCP information void?

(Not a professional, just somebody following the news, so my terminology is off.) The latest news from today is that they entered the air control zone of Guangzhou not long before the crash. The ATC noticed that they started a steep dive and repeatedly tried to reach them, but got no reply whatsoever until the end.

Looks like your speed qualification assumptions are wrong. The FR24 speed data is Ground Speed. So, when the airplane goes down vertically, the Ground Speed will show zero, while the TAS can and will be enormous, largely above VNE, even the speed of sound (hence the reports about "booms") can be reachable.

Your assumption about a decreasing "speed" in the FR24 data, happening before the upset is wrong. Only once the upset starts, the Ground Speed goes down, understandable, since the airplane is diving with more 20K ft/min. So no anomaly in the reported FR24 speeds.

Somehow, this forum is leaking valuable postings, something I have noticed more and more, especially over the past 5-10 years.

Of course, the trim switches are as you describe, though that does not imply, a trim-runaway is impossible. Hence, the presence of the double trim cut-off switches. These are there, because these are regulatory and technically needed.

I keep coming back to the (speculated and in no way confirmed) fact that they were TOD.
TOD in the 738 is fairly benign;
A few buttons punched on the FMC- VNAV Checked, etc and on the MCP- ALT put in (and depending on whether it was VNAV or only LNAV - V/S - can you really go sooo wrong doing any of that? Other FMC Inputs at that time pertain to Flap select for Landing, etc - nothing to do with anything directly connected to changing the physical config of the aircraft at that time.
and the Checklist is only;

Pressurization
Recall
Autobrake
Landing Data
Approach Briefing

So there's nothing mechanical there that moves anything physical on the airframe. (Apart from Autobrake dial on the MIP)
It's so wierd - TOD is like the last phase of flight where something suddenly goes so completely wrong. The only thing you can do on the MCP (and that's the only thing you actually touch apart from selecting your Autobrake setting on the MIP) at TOD to crash the aircraft is dial in ALT 0 and V/S 8000/FPM. That will get you spat out. But to do that the bloke sitting next to you - checking your work - would have something to say about it. And if it was me - I'd challenge you as to why you'd dialled in those Extreme MCP ALTS and V/S and if you wearn't making sense I'd probably knock you out and have you removed from the cockpit.

It doesn't make sense - it just fell out of the sodding sky. For me that makes it Mech Fail. Something went 'Twang' and it became unrecoverable (with the best will in the World being flown up front) but I have absolutely no idea how or why. But I am very anxious to know.

RIP

Barring an unusual CCP exception, mainland China Covid regulations will require any country of aircraft design, aircraft manufacturer, etc representatives to quarantine for 3 weeks (first, 2 weeks in mainland Central Government-quarantine hotel plus 1 additional week in other hotel/residence). Potentially, less than ideal 3 week+ investigation observation delay.

The profile plot from post #52 is interesting as it does not show a "vertical" drop, probably more likely between 30-40 deg trajectory. I also agree with a post that highlighted the two ADSB blips where there is an extended gap between responses of say 15 seconds, where both steep descents seem to originate, was there some sort of electrical fault or factor? From both ADSB cutouts the aircraft initiates a steep descent and lurches left, from what the plot shows. After the first there seems to be a turn of sorts back to the right and some recovery action by 10,000 feet then a second gap in returns and it goes back into the final steeper profile.

Doing a quick and dirty calculation on the g force the black box is likely to have experienced on impact (based on velocity figures that were calculated earlier in the thread), the memory modules will have survived by a fairly comfortable margin

Spoke to my son this morning (B738 pilot here in Australia) and the consensus amongst his colleagues echoed your sentiments above

I suspect it's chicken and egg speculation now, until the recorders are recovered and read:

How did the crew's actions at TOD contribute to this catastrophic event, or had something failed on the plane just prior to TOD

My thoughts are with the families of those lost


Retired B driver

My one flight on a chinese domestic airline was just over 25 years ago and it was a Boeing but cant recall the model. What I do recall is at TOD the autopilot was disengaged and close to full spoilers deployed. So it was a loud rough decent for us. Back then the flight crew were straight from the chinese airforrce and their level of English was basic. I am sure things have improved there since then. I am a retired CPL.

Estimate speed
 

Someone with more video analysis skills than me could provide a rough speed calculation based on the video using the aircraft lenght as scale reference? Surely it won’t be 100% accurate but I think that the Ground Speed reported from FR24 data is far from accurate and is not even close to the TAS experienced in the final moments. With 3000ft/min a 738 can barely keep 300knots indicated. With 30.000fpm there is no way the speed was lower than 600kts especially with so much potential energy from FL300.

edit: if no such speed was ever reached than a recovery attempt should be realistic, and if a recovery was even partially successful that means that the initial upset was probably not as catastrophic as someone might expect.

Seriously, basic knowledge of China ATC 25 years ago would tell you the crew vey rarely get to make decisions about descent profiles.

This is the dashcam footage you speak of:

It's interesting you say that as I used to work next to a major runway and have witnessed many takeoffs and landings. It was always the China Eastern planes that came in hot and heavy (as I called it) and were the loudest of all the 737s. We would make a joke...oh it''s another CE landing again...

The aircraft was in maintenance for two full days days before the crash.

https://cimg4.ibsrv.net/gimg/pprune....72aff8bade.jpg