FZ981 -- 61 die; plane explodes after crashing at high speed on landing

[KL-666]

Possible scenario, Jwocky. But we never heard anything about flaps. Another scenario could be: flaps retracted, high speed, low weight. Hard to level off then too. We'll have to wait till officials release any information about flaps.

Kind regards, Vincent

[jwocky]

Yes, but I wondered. The speed was not that high, only the VS was quite impressive and for the approach, the flaps should have been already out at 30 to 40. And nobody talks about flaps which is even weirder because well, if the flaps weren't out in end approach it would have been bad, so, the AP may had a reason fir extreme trim, but then, wouldn't that be still ab. 35% of the whole elevator way?

[KL-666]

Thinking of it, it does not matter in what trim position a pilot takes over. With nose-down, first reaction is pull the elevators. If that has not enough effect, then the natural reaction is to immediately trim up to get more effect. The trim is not for nothing made at the thumb of the pilot on the yoke.

For a well trained pilot strange trim positions should never be a problem. Untrained pilots forget there is such thing as a trim, because they have relied too much on autotrim during their flashy impressing girls with expensive cars career.

Kind regards, Vincent

[KL-666]

Today the Russian investigators released another update. They are not giving much information, nothing about flaps, gear, autopilot.

As the crew were proceeding with another manual approach, they decided to go around again at a height of 220 meters (4 km before the runway) and initiated climb setting the engine to takeoff thrust. At a height of 900 m there was a simultaneous control column nose down input and stabilizer 5-degree nose down deflection, resulting in abrupt descent with negative vertical acceleration of -1g. The following crew actions to recover did not allow to avoid an impact with the ground. The impact occurred with a speed of over 600 km/h over 50 degrees nose down.

http://mak-iac.org/en/rassledovaniya/boeing-737-800-a6-fdn-19-03-2016

The interesting bits are:

It was a manual approach and a manual nose-down action (control column nose down input). No information about whether the autopilot had been enabled between the start of go-around and nose-down action. About the stabilizer deflection they are not so clear who did it. But they say trimming occurred simultaneous with control column input. Which suggests manual action, because auto trim kicks in a few seconds after enduring control column input.

Now there are more questions than answers. Why would they level off manually and rather abrupt (overreacting) at 900 meters (3000 ft) while they planned to go to fl 80? If a wrong auto pilot setting would have done it, i would have understood. But manually leveling off at the wrong alt?! really weird.

[edit]

Well i can think of one reason: They may have blindly followed the cross hairs of the flight director without it being reprogrammed for the go-around. Here is what the FAA has to say about flight directors:

The FD is designed with the computational power to
accomplish these tasks and usually displays the indications to
the pilot for guidance as well. Most flight directors accept data
input from the air data computer (ADC), Attitude Heading
Reference System (AHRS), navigation sources, the pilot’s
control panel, and the autopilot servo feedback, to name
some examples. The downside is that you must program the
FD to display what you are to do. If you do not preprogram
the FD in time, or correctly, FD guidance may be inaccurate.

............

Common Error: Blindly Following Flight Director Cues

The convenience of flight director cues can invite fixation or
overreliance on the part of the pilot. As with all automated
systems, you must remain aware of the overall situation.
Never assume that flight director cues are following a route
or course that is free from error. Rather, be sure to include
navigation instruments and sources in your scan. Remember,
the equipment will usually perform exactly as programmed.
Always compare the displays to ensure that all indications
agree. If in doubt, fly the aircraft to remain on cleared track
and altitude, and reduce automation to as minimal as possible
during the problem processing period. The first priority for
a pilot always is to fly the aircraft.

http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/advanced_avionics_handbook/media/aah_ch04.pdf

Anyone noticed the word "scan" in the above? It should be such an obvious thing for pilots, that it needs no further explanation in this text.

[/edit]

Kind regards, Vincent

[jwocky]

I slowly think, the A/P wasn't engaged anymore since the begin of the second approach. How reliable is the report that the trim change and the column input were really at the same time?

[KL-666]

As reliable as the investigating team itself can be. The link below the quote is to the origin MAK, the Russian NTSB.

Kind regards, Vincent

[HJ1an]

"The Interstate Aviation Committee confirms a previous disclosure, by the federal air transport regulator, that the stabiliser shift occurred at a height of 900m, as the aircraft climbed away from Rostov-on-Don during a night-time go-around.

It states that “simultaneously” with the yoke being pushed in the direction away from the crew, the stabiliser deflected to a 5° nose-down position. The aircraft rapidly pitched down and dived with a pitch exceeding 50°.

“Subsequent actions of the crew could not prevent the aircraft’s collision with the ground,” says the inquiry.

It says the aircraft impacted at a speed of more than 320kt. The jet disintegrated with the loss of all 62 occupants.

Investigators have not reached conclusions over the reasons for the findings into the 19 March crash involving flight FZ981.

So I don't get this.

[ “..simultaneously” with the yoke being pushed in the direction away from the crew, the stabiliser deflected to a 5° nose-down position. The aircraft rapidly pitched down and dived with a pitch exceeding 50°. ]

Doesn't say for how long they were in this state, but it would seem like spartial disorientation would keep them like that to the point of no return.

Also it was stated that landing attempt was apparently done manually.

https://www.flightglobal.com/news/articles/flydubai-crash-yoke-push-simultaneous-with-stabil-424011/

[KL-666]

Well, there is an interim report now.

http://mak-iac.org/upload/iblock/19b/Interim%20Report%20A6-FDN%20%28en%29.pdf

It does not add much to what was released earlier by the investigating team. And it is rather hard to read, that English written by Russians. I'll just rephrase the given facts in my own words here.

1) The approach was manual and controlled following the ils on the flight director quite accurate.
2) At 700 ft they decide to go-around with toga at a climb rate of 4000 ft/min and a pitch up to 18 degrees.
3) In this climb landing gear was retracted and flaps set back to 15 degrees.
4) At 1900 ft the climb rate is decreased by control column input, allowing for the speed to go over 200 kts which caused the flaps to automatically retract to 10 degrees.
5) The engine thrust was decreased shortly, slowing the plane enough to extend flaps again to 15 degrees.
6) But immediately after that toga is selected again causing a speed increase and automatic flap retraction to 10 degrees again.
7) The column is pulled to a climb at 3000 ft/min with the configuration of the former point 6) unchanged.
8) At 3000 ft there was a simultaneous control column nose down input, and stabilizer nose down input on the yoke switch that lasted 12 seconds causing a deflection from -2,5 deg (6,5 units) to +2,5 deg (1,5 units).
9) With these inputs, at some 300 ft higher, the climb turned into a dive.

Very interesting are the recommendations at the end of the document. They are about better training of go-arounds with a *light* aircraft.

What i make of this sequence of events is that insisting on toga for the go-around with this light plane, caused a too wild and fast ride which made the pilots run behind the facts all the time.

There is no mention on why the pilots insisted on toga. But there is a very well known reason for such behaviour. Pilots often do not posses the mental model in their head to manipulate thrust in a way that suits the balance of energy in a particular situation. Having used auto thrust all their lives, they deem that max thrust is the safest bet for a go-around. Thereby proving that they do not understand the energy management in which (lack of) weight is also a factor.

Kind regards, Vincent

[IAHM-COL]

Isn't 12 seconds a long time to be pointing the yoke and stabilizer "down" @3000 ft?

[KL-666]

If you are in a high speed and high climb rate climb, and want to level off, then normal procedure would be to pull thrust and push yoke. Followed by trim to get the yoke neutral to the new situation, probably somewhat down.

But these guys demonstrated at 1900 ft that they just push the yoke without managing throttle. This caused increase of speed and busting flap speed.

There is no reason to expect they did different at 3000 ft. Just pushed the yoke while still on toga. In that case the plane speeds up rapidly when leveling off. Needing a huge push of the yoke and a huge amount of trim down to relieve the yoke to neutral.

What happened next is not mentioned. One can not continue speeding up level for ever. So i suspect they eventually pulled the throttle (not mentioned in this interim report). In that case the extreme nose down trim is not appropriate anymore, and you start to dive.

Flying is all about managing energy with pitch and power. If you do only pitch without adjusting power, you speed up or slow down dramatically. This is the stuff that is often forgotten to be trained at many airlines.

Kind regards, Vincent