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.