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.

All 737-800s at MU are grounded
My hunch is a runaway trim.

says who? FR24 seems to disagree, there are about ten of their 738s in flight as of this posting

Interesting new data in the more granular data from Flightradar24

If the reporting is correct it seems to show that for a short period the crew recovered, gained altitude before the dive resumed.

https://cimg2.ibsrv.net/gimg/pprune....4dcaf384fd.png

China Eastern 737-800 MU5735 incident
 

This appears to be the lower outer wing structure, with the fuel tank blow out panels missing,

https://cimg9.ibsrv.net/gimg/pprune....2f0df2f4f7.jpg
From Weibo, Aircraft debris near the scene of the accident.

Guys, do you remember Germanwings? I stated early on in the discussion that a plane doesn't go from cruise to crash very quickly. I was immediately mobbed on here when I suggested it was suicide. Now the bells are ringing again nearly 7 years to this day (24th Mar) and again I am being mobbed for saying this looks like a suicide event.

I have been on PPRuNe a lot longer than most that say don't speculate.
I do not fly the 737 but many on here do and this will be unfortunately another learning event for us all.

It is healthy for us to have a grown up discussion regarding accidents. This is how we learn in the industry. Our checklists, procedures and everything we do are unfortunately written in the blood of our deceased colleagues.

From eagle 21 picture. Well the rudder is composite and the blue ends at the trailing edge; strange how some rivets are torn through and others just popped; the aluminium non painted piece looks whole and with no external paintwork unlikely the nose of the rudder, presume could be a back closing panel of the V.fin where the nose of the rudder swings, the green bracket also that area. and so rudder flutter and delamination less likely in MHO.
JAL123 a B747 RPB repair failure leading to an over pressurisation in the tail section comes to mind, though it is unlikely to have been started in this case by a cabin air loss as blow out vents are now designed to cope with this..

Plus the aircraft was at cruise for quite some time.
If it was a structural failure due to pressurization, it would have occurred a lot sooner in the flight (i.e. during climb, just like JAL123 and CAL611).

Speed vs. vertical speed doesn't seem to make much sense. Maybe timing issue between the columns?

In the 3 recent incidents of 737 runaway trim (2 MAXs and Fly Dubai at Rostov) the descent angle with the runaway nose down trim was at a max about 45 degrees. The two social media videos of this incident indicate a far greater descent angle.

Plus there was a period of erratic flight prior to the final nose down pitch and descent, this incident seems to have suffered an almost instant controlled flight in cruise to near vertical descent.

Photos of large pieces of debris on the ground do not seem consistent with being part of the plane when it slammed into the ground. Detached prior? Location where found??

If you mean the cockpit jump seats must have been occupied, not all 73’s come with the second JS. 5 cabin crew and 2 pilots, might have simply meant that 2 cabin crew were in the CC jump seats.

Last time I saw a flight track like that and a vertical dive to the end, was the Alaska Airlines loss of Stab.

Most Chinese airlines have at least 3 or sometimes 4 pilots. I've seen many crews with Capt, FO, SO, and 1 stripe cadets walking to the airplane. So my guess is 4 pilots and 5 cabin crew.

You are correct...however there was another suicide crash by a disgruntled asian pilot, that looks like this. I think it was Silk Air in Indonesia.

how about cut-off broken rudder like the a310 in new york in 2001?

Who remembers the Air Nippon 737-700 incident where the copilot was trying to let the Captain back into the cockpit and accidentally mistook the rudder trim wheel for the cockpit door switch? The pilot ended up putting the aircraft in a 30000ft/min descent with almost full uncommanded rudder deflection.

Unfortunately I can’t post links because I’m below 10 posts but a quick Google of ANA 117 will come up with results.

It was A300, not A310.

A rudder hard-over and the resulting bank could likely result in these sorts of rates of descent.

Though personally my mind is quite open as to the cause at this stage.

Initially I'd speculated a deep stall, with the crew unable to get the nose down based on the initial reported VS similar to AF447, however the since revealed fairly consistent and then increasing GS seems to make this appear less likely for now as well as the cruise altitude of FL290 would have a significant margin away from coffin corner.

In my experience emergency descents even with full speed-brake in the Mach to Speed transition only tend to result in a VS of 8,000-9,000 fpm before quickly stabilising at about 4,000-5,000fpm once the transition to speed is complete which seems incompatible with this VS, particularly given the aircraft was pretty much at the MACH/Speed cross over altitude or there abouts.

Wings falling off or other structural failure seems a possibility, this should be able to be determined within the next few days should the debris of the wings or tailplane be found a distance from the main fuselage wreckage.

A suicide possibility exists, but it would have to be very drastic to get the airplane into that sort of attitude, and then the short recovery of altitude before the final dive seems to indicate there was an attempt to recover. IIRC the German Wings incident involved a much more tame 3,500-4,000fpm descent as well with no attempted recovery.

All speculation for the next while.

Could trim or pilot input get the attitude so nose down? I would think you would need a complete failure of the elevator and/or horizontal tail.

stand corrected sir