Boeing 737 Max8 Aircraft Crashes and Investigations [Part 1] 20

[itsmoked]

Indonesian 737 Max 8 - Splashed

Most reports I've seen mention the aircraft had an 'undisclosed issue' before take-off. Does anyone know what that was?

Surely the crew was in contact and reporting something during the relatively long disaster.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[itsmoked]

Ian; Thanks for that description of sliding towards uncontrolled flight. Pretty subtle. Nasty! I know high performance airliners have a surprisingly small speed window at altitude for not stalling from the 447 disaster. I can see how in fairly short time you could exit that window, especially in a moonless night over an ocean.

For pitot speed instrument failures isn't GPS more than capable to get you air speed close enough to work. Oh, it's the fact that the air mass itself could be moving significantly isn't it?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[MintJulep]

Oh, it's the fact that the air mass itself could be moving significantly isn't it?

That. And density.

 

[itsmoked]

Ah, that's right! A rather key aspect of lift and drag.

Thanks Mint.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Alistair_Heaton]

Density tends to cancel itself out when the aircraft is in the air. And being in a moving mass of air is more a navigational issue than a flight performance issue until you get a sudden change in that movement which we term wind shear. Then the momentum of the aircraft comes into play and you can get suddenly relative drops or increases in airspeed. But steady state the aircraft doesn't know its in a moving mass of air.

Ground speed off the GPS is used on the flyby wire aircraft namely airbus but I have only ever flown one of them twice in the sim for an hour and haven't done the 5 weeks ground school conversion onto a airbus type so don't want to comment on how that works I just know on approach its involved somehow but quiet what it does I have no clue.

GPS quality is governed by a thing called RAIM the system automatically works out a quality factor and tells you when it drops below a certain value for a particular phase of flight or airspace. In the case of doing GPS approaches (RNP) we have indicators of what class of signal we are receiving and if its below whats mandated the box will refuse to give us the guidance to carry out the approach.

Now the thing that really kills lift is when the angle of attack of the aircraft exceeds the critical angle and the aircraft goes into a stall. There is a sudden drop in the coefficient of lift as the air flow breaks away from its lamina flow over the aerofoil and turbulent flow starts.

Now as such on civilian aircraft the only indication of angle of attack (AoA) is the attitude of the aircraft. The data is available because the stall protection system has usually 2 or more AoA vanes to get data from. And when it senses your near the limits it triggers various responses in the cockpit which are tactile(thing called a stick shaker) noise, and visual. If the AoA increases further it can then trigger a thing called stick push which applied nose down control input thus reducing the AoA.

Now what your actually doing in the cockpit when you fly a speed is set a AoA for what you want. For takeoff and landing its defined from the critical angle of attack and after departure you are setting the most efficient AoA from the lift drag curve. Its the same angle of attack its just the speed varies with weight. It is possible to have zero airspeed and not be at the critical angle of attack. But we don't do that sort of nonsense in transport aircraft.

No why do pilots fly airspeed not AoA…… historical and the whole training setup is geared towards nailing an airspeed.

I don't want to name my airline. The media dept does search the net for the airline name and its part of our contract that us pilots don't make statements on the company's behalf. Although nothing I have said is controversial they don't tell me how to fly a plane and I don't step on there toes.

Now I have to go throw an aircraft at the ground 4 times.

I will leave you with a training video which covers this subject.

https://youtu.be/WfNBmZy1Yuc?list=PLAjYL1_ZduxTtSkF8D9H5Hn2eGsogUpu6

This series of training lectures are extremely good. Note the date they were made. These issues have been current for years and years. They are long every year we have 5 days of similar ground school looking at accident causes so we can hopefully trap the errors before they occur. IN the sim which occurs every 6 months for 2 day we recreate situations to see how to deal with them.

https://www.youtube.com/playlist?list=PLAjYL1_ZduxTtSkF8D9H5Hn2eGsogUpu6

please note my comments above are extremely simplistic from both a pilots point of view and engineering. To behonest I really don't have time to provide a more comprehensive reply.

 

[VEBill]

Contrast Air France 447 (crashed in the Atlantic) and US Airways Flight 1549 (landed in the Hudson).

An obvious and highly significant difference is that Capt Sullenberger concentrated on flying the airplane (while copilot Skiles was busy troubleshooting). According to the information I've seen, that division of responsibilities, ensuring that somebody was 'flying the plane', perhaps didn't occur on other incidents that ended badly.

In such emergencies, perhaps the displays on the left side of the cockpit should flash "Fly the plane!" in large letters.

Let the right seat do the system failure troubleshooting.

[sub](Acknowledge in advance this is a vast oversimplification; it's intended to make the rather obvious point about CRM, user interfaces, distractions of too many error messages and Human Factors.)[/sub]

 

[IRstuff]

That type of tunnel vision has been the root cause of more than a few accidents. Another, similar, cause is when the cockpit crew is afraid of the captain and doesn't articulate that there's a problem.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[SwinnyGG]

GPS is an open loop system as well- but the inputs into any system processing GPS information are less corruptible than something like a pitot tube that can suffer from water or ice.

I can't imagine that GPS would ever be able to fully substitute for an on-aircraft, physical way of measuring airspeed. Just put an aircraft in the jet stream, and your ground speed and airspeed could be different by more than 100 kn; the position, velocity, etc of the jet stream aren't known precisely enough that you'd be able to use GPS to cancel out its effect all the time.

 

[debodine]

I have to agree with jgKRI about GPS usage for airspeed not being viable. GPS can be used to precisely determine position, and from precise position to precise position, the velocity between the positions (ground speed), and I have even read of airborne experiments where four GPS receivers on an aircraft (nose, tail, left wingtip, right wingtip) did a pretty good job of determining roll, pitch and yaw. But to determine the airspeed within a moving mass of air that can't currently be accurately characterized with available technology, that remains a goal yet to be established and reached.

 

[Alistair_Heaton]

Why do you need airspeed?

There is age old system that pilots are taught.

Aviate navigate then communicate.

Btw that's my day just finished 280 pax moved. 10 cups of tea. 7 tons of fuels burnt. And the aircraft in the same state as when I signed for it this morning.

 

[itsmoked]

cockpit crew is afraid of the captain

Tenerife captain of the Rhine.

I wonder if a simple heated probe being a mass-flow sensor coupled with a altimeter couldn't be used as a speed system. The barometer/altimeter to give air density the massflow with the density to give speed.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Alistair_Heaton]

you got where I am coming from. There are other ways of instrumenting aircraft to get what you need. But we are still using basically ww1 tech.

 

[Alistair_Heaton]

But you also missed the time difference between my posts. I started in the dark and last landing was in the dark.


The dealing with issues at the beginning of the shift is shall we say different to the last sector of the day. The human limitations is also a major influence.

 

[GregLocock]

" four GPS receivers on an aircraft (nose, tail, left wingtip, right wingtip) did a pretty good job of determining roll, pitch and yaw."

Using differential GPS (don't ask me) we no longer need conventional instruments (accelerometers, gyros, correvits) to do much of my vehicle dynamics work. But we can't measure windspeed using them!

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[Comcokid]

This article indicates the AOA (Angle-of-Attack) sensors may be part of the issue in this crash.

https://phys.org/news/2018-11-boeing-issues-advice-sensors-indonesia.html

 

[Alistair_Heaton]

that's called spurious stick shaker.

Normally when the stick shaker goes off it means your approaching the stall. So you do the stall recovery memory actions

Which are

1. reduce the pitch attitude.
2. roll wings level
3. power to max
4. once airspeed increase pitch for climb.
5. clean up
6. normal flight at safe altitude.

I might add this is the European recovery procedure. American pilots do it differently normally even though NASA and the FAA have told them to do it the same as us.

Spurious stick shaker we can kill with a single button push. But we are back to recognising that it is indeed spurious.

During departure your going to be at high power levels anyway and if you reduce the attitude to below the horizon the airspeed will within a couple of second exceed Vmo (max operating speed) and another alarm will start going off. At this point you have conflicting alarms one for high speed and one for low.

I have had this issue 3 times in my 8000 hours. Twice on the analog machine which has tabs on the wing which lift when the static point starts going under the foil. And once on a AoA vane stall system. Again for me the biggest problem was trying to convince my colleague we were no where near stalling.

Pitot tube blockage is another one which is interesting it makes the airspeed indicate that its rapidly increasing ie it turns the airspeed indicator into an altimeter. Increasing airspeed in the climb would normally lead to a pitch up to reduce it. If you pitch up to much you hit critical angle of attach and stall. Had that a couple of times on the analogue machine.

 

[TehMightyEngineer]

Alistair, from what I'm reading it sounds like the AOA discrepancy kicked on an automated nose-down trim, kind of like a stick pusher but more gradual and able to be overrode by the pilot either with yoke forces or via manually actuating the trim system. This kind of stall protection system is beyond my experience, though I do have training regarding runaway trim. Can you shed some light on what this article and the service bulletin from Boeing is discussing?

American pilots do it differently normally

We do? Your memory action procedure is the same as mine; though again I don't fly anything bigger than 4 seats so not sure if the airlines are doing anything different.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[Alistair_Heaton]

Yes there is a couple of areas which differ one is this stall recovery and the other upset recovery.

There is a fixation about not loosing altitude. So the power is applied while lowering the nose as a combined action. Then the wings levelled and then the pitch for climb. The way we are taught is almost a pause between each item. The problem with applying at the same time especially in swept wing jets is the pitch power couple. By putting the power in your getting a huge up couple which increases your AoA and can make maters worse. Then the fixation of not loosing altitude means that the pitch for climb occurs to abruptly which can and does frequently result in a secondary deeper stall. Most will try and power out which works on the stickshaker because its a incipient stall recovery and the plane isn't actually stalled yet. The only way to unstall a plane is to reduce the AoA. No difference between a C150 and a 747. if you have been taught the above method then its slowly working its way through.

The upset recovery is another issue, a lot of US pilots have been taught to lift the wing using rudder. This is fine if its a singular event ie you will get away with it even though there is more drag and the plane is completely out of balance. But if you have hit vortex with rapidly changing air flow it can result in a cyclic application of flight controls sometimes full deflection at way over rough airspeed. The classic example of this is AA587, after 5-6 cyclic applications of full rudder the tail failed.

Last BFR I did the FAA instructor really was not happy with me doing it the European way and that was 10 years ago. And some of our new pilots who did their initial training in the US are still coming into the sim with the American way of dealing with these situations so its still being taught.

 

[Alistair_Heaton]

As I said previously I am not 737 rated but again we have a trim runaway procedure on all aircraft fitted with electric trim. Its one button/switch to kill the electrical trim system. The Boeings have a manual trim wheel as well and its scary loud and fast when it moves. The q400 if the trim system is active more than 5 seconds then an audible alarm sounds. And if ours fail we just have to hold it untrimmed which if its been allowed to go fully forward is a bit of sweat and swearing flaring.

 

[TehMightyEngineer]

There is a fixation about not loosing altitude.

Ah, yep, I see the difference you're talking about and indeed I was trained the "American" way. When I did my instrument training there was some emphasis on unloading the wings first prior to rolling and recovering. We're still grilled about altitude loss, though. If we pause too much we fail the procedure due to altitude loss. I think part of it is primary training occurs in piston singles which are much more forgiving to recovery technique.

The upset recovery is another issue, a lot of US pilots have been taught to lift the wing using rudder.

I believe this has been changed; when I did my instrument training recently the upset recovery was taught to me as: unload the wings, level via ailerons and coordinated rudder, recover from the vertical upset, and set power to return to previous altitude. Still, I imagine many older instructors are teaching the older methods.

trim runaway procedure on all aircraft fitted with electric trim

In the G1000 Cessna I fly the procedure is identical. Holding A/P disc kills electric trim, if trim is in motion for more than a few seconds we get an audible warning, and if it gets out of hand we can manually override the A/P clutches with a complimentary arm workout. Funny how the technically advanced GA aircraft are becoming more and more like a single-pilot jet in terms of procedures and avionics.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[Alistair_Heaton]

to be honest mate I am legal to fly this. And your G1000 is fancier than the Q400

And this