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

 

[Alistair_Heaton]

opps chose the wrong picture of the Jetstream cockpit its has a FMS and auto pilot the ones I fly have no autopilot and this is the gps.

 

[TehMightyEngineer]

Heh, the G1000 makes single pilot IFR so simple. I occasionally go up and do some IFR work in an old C152 just to make sure I can still fly without a computer doing 90% of the work for me. Not going to be one of those pilots who can only follow the magenta line.

Anyway, back to the topic; what I'm reading some component was replaced by the airline prior to the fatal flight. I'm sure the accident chain will include all parties but this is seeming more and more like a Boeing design issue. Too soon to make that judgement you think?

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

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

 

[TehMightyEngineer]

For those playing at home; here's the cockpit of the G1000 system Alstair and I are talking about:

Modern single engine trainer aircraft these days often have more advanced avionics than many of the older airline fleets. Nothing wrong with the older tech of course and the cost to update doesn't make sense; still amusing though.

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

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

 

[Alistair_Heaton]

Speed Trim SystemThe Speed Trim System (STS) is a speed stability augmentation system designed to improve flight characteristics during operations with a low gross weight, aft center of gravity and high thrust when the autopilot is not engaged. The purpose of the STS is to return the airplane to a trimmed speed by commanding the stabilizer in a direction opposite the speed change. The STS monitors inputs of stabilizer position, thrust lever position, airspeed and vertical speed and then trims the stabilizer using the autopilot stabilizer trim. As the airplane speed increases or decreases from the trimmed speed, the stabilizer is commanded in the direction to return the airplane to the trimmed speed. This increases control column forces to force the airplane to return to the trimmed speed. As the airplane returns to the trimmed speed, the STS commanded stabilizer movement is removed.

STS operates most frequently during takeoffs, climb and go-arounds. Conditions for speed trim operation are listed below:•STS Mach gain is fully enabled between 100 KIAS and Mach 0.60 with a fadeout to zero by Mach 0.68
•10 seconds after takeoff
•5 seconds following release of trim switches
•Autopilot not engaged
•Sensing of trim requirement

 

[Alistair_Heaton]

Found that on the system in question although quiet how that links into the AoA system is obviously a need to know system knowledge.

And way way to soon to make anything other than interest comments as we have been doing on the general systems how they work and human performance issues.

One of the reason why I registered was partly to do with my background as an engineer but also because with hindsight I realised that my engineering training was really quiet poor at highlight the human interaction and reaction aspects of the projects I was involved with. And from my lurking particularly this forum section I saw what a great bunch of thinking and opened minded people were participating.

You just have to look at that ergonomic heap of shite which is the Jetstream (35 year old design) and compare it with the Q400 which is 15 years old to see how things have progressed. But have they progressed too far? Is there too much data being pushed towards the user. This has implications in several applications I have "gone back" to an old haunt in Nuclear to teach Crew resource management and Threat Error Management (TEM), also I have taught medics as well and got them to use checklists.

As engineers its something to think about.

I am opened minded if its a design issue or human factors/training. You have to remember that the 737 would not pass current certification standards if it was a green fields design. Its been stretched digitised and tinkered with all on the back of a 1960's design and the certification standards of the day. Similar to the DXB EK521k which is now going through the courts claiming design failure. As a punter involved yes have your day in court.... but honestly as a pilot you don't just press a button and expect the machine to do as you expect. You verify its the correct button, then you press it and then you verify again that its had the effect you want. You press a button wanting toga power and you don't see the needles rising and you don't feel a kick in the pants as the power winds up... you bloody well shove the power levers forward and pitch the nose to the required attitude.

 

[itsmoked]

The PhyOrg article states differing "AoA of 20°".

That seems huge to me. What are the typical values of AoA seen in airliner operations?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Alistair_Heaton]

yes 0 to about 15 degrees anything more than that and your into critical angle of attack which means the stall system is triggered.

I maybe guilty of presuming that people know what the critical angle of attack is and its approximate value in my posts... I do apologise.

As soon as I saw 20 deg split I presumed the stick shaker system was triggered.

0 is extremely rare and would be extremely uncomfortable to the pax. The wing incidence which is shall we say welded is about 1-2 degs and we would normally cruise with 1-2 deg nose pitch up giving about 3 deg in the cruise but this does depend on what cost index we are using and what the "sweet" AoA is for coefficient of lift and Coefficient of Drag.

 

[VEBill]

If pitot tubes keep causing problems (system failures, ice build-up, water, mud dauber wasps, masking tape leftover from painting....the list goes on and on), then it may be time to consider back-up systems, based on an alternate technology, with a well-designed method of combining the information (Kalman filter concept).

Quora says, "Hot wire anemometers arranged in a circular pattern can determine both wind speed and direction. Another method is using ultrasonic based sensors." These used to measure wind.

Lasers are also mentioned, in terms of tracking microscopic airborne particles.

And with GPS as another input for our purposes.

Strings attached to the windscreen and sidescreens like gliders?

 

[TehMightyEngineer]

0 is extremely rare and would be extremely uncomfortable to the pax really, really fun!

But, yes, most (all?) planes cruise with a few degrees of AoA. Bernoulli and Newton generally both are at work to make a wing fly.

cost index we are using and what the "sweet" AoA is for coefficient of lift and Coefficient of Drag.

Oh, do expand on this. Is AoA how you target efficiency for cruise flight? (dragging us off topic, sorry)

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

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

 

[TehMightyEngineer]

then it may be time to consider back-up systems

You're not wrong but how would any of these systems not also be susceptible to the same failures as a pitot-static system?

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

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

 

[SwinnyGG]

20 degree differential between two AoA data streams is huge.

There's no exact numbers- optimal angle of attack for an airfoil in any particular steady-state flight condition depends on aircraft weight/CG position, mach number, density altitude, and position on the wing. Position on the wing is interesting to keep in mind, because most aircraft wings are swept combinations of several, sometimes many, individual foil shapes and there is typically twist in the chord angle between the root and the tip of the wing; so the 'true' AOA is different at any given point on the wing. The reason for the airfoil twist in the wing is actually to control where stall conditions first arise on the wing to make the stall more progressive and easier to control/recover.

Anyway. Most conventional airfoil shapes will have a stall angle between 15 and 20 degrees, and actual operating aoa will be much lower, say 2-4 degrees.

So yeah, having two aoa streams, one telling you that the aoa is 2 degrees and the other saying it's 22 degrees is potentially really, really bad.

 

[Alistair_Heaton]

to be honest I reckon aircraft fly because of newton but are controlled because of Bernoulli.

If you have a flat piece of wood at an angle to an airflow it will produce lift and give a force vector.

We don't get AoA in the cockpit but most performance stuff is related to AoA and where you are in the drag curve Vy will give you the best performance because it gives you the least drag. But there are other financial cost and because the increase in drag is not linear then they adjust the cost index to take into account the fuel price.

Because we can't set a AoA we get an app or pages of performance data which links weight to power requirements which is a round about way leads to a AoA being set. There is another fudge factor built in which takes into account head and tail winds so we fly faster in a head wind and slower in a tail wind which factors in the maint costs per hour of operation. Also the air temp changes the settings and the fuel burn. IN the jets with auto throttles its all done by the Flight management system. Turboprop drivers have to do it manually we look at the temp, head/tail wind, weight and altitude and put them into an app on a Ipad and then it spits out a torque setting. We set it and order a cup of tea. last flight of the day we may choose to ignore the app especially if out mates are flying and its a race to get home first.

 

[VEBill]

...susceptible to the same failures as a pitot-static system?

The goal would be to reduce the odds, so that Airspeed Indicator issues might be persuaded to move way down the list.

Commonality can allow common failure modes, in spite of redundancy. e.g. AF447.

(By way of counter-example: If I recall correctly, the Space Shuttle famously had intentionally diverse flight control computers. Triple redundant, but all three different. Different hardware and different software.)

As has been noted, Human Factors is a major contributing factor with these incidents. So how backups are all integrated and presented seems like the difficult aspect. Multiple diverse sensors is the relatively easier design aspect.

The complex interactions between bad or confusing data and the pilots, leading to an otherwise functional aircraft to crash, seems to be a recurring theme. Engineering or designing out these sorts of issues seems like an issue worth addressing.

I'm not an SME on this topic. These are just opinions based on what I've seen or read.

 

[Alistair_Heaton]

The space shuttle even with its redundancy still ended up with instrument failures and some hairy landings.

All the pilots on the stick were test pilots who have super human data processing ability's. They still screwed it up occasionally.

And as the poster above says the changing of the design and the presentation of data is constantly evolving.

In the next 12 months I will be getting trained up on this aircraft.

Still fly's the same as the Jetstream. No paper no checklists, only memory item is to put your o2 mask on if there is smoke.

 

[TehMightyEngineer]

Looks like an A350. What's the giant red button do?

Has Airbus finally made it so you have some feedback on what each side stick is doing? (i.e. Airfrance crash)

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

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

 

[SwinnyGG]

That's the eject button, obviously

 

[Alistair_Heaton]

It is an airbus but a Canadian one not a French one ;-)

I haven't got a clue what the big red button does. I suspect its a flight test aircraft. They are set up a bit weird because they have huge water tanks in the back and they can pump between them to do the CofG testing and variable weight for the envelope testing.

Always gets the chemtrail lot excited when they see funny buttons and water tanks in the back. closely followed by the flat earth lot asking if the water is flat or at an angle.

I don't remember seeing it on our fleet the couple of times I have jumpseated.

 

[thebard3]

That's the eject button, obviously

I think it's an emergency stop.

Brad Waybright

It's all okay as long as it's okay.

 

[Sparweb]

Strikes me that the big red buttons are associated with the special red panel in the center console.
Shifting water back/forward, with a valve Open/Close/Fail annunciator on the red panel... perhaps a "dump" on the panic button? Just guessing.
Back in the day, Canadair (predecessor to Bombardier) had a test flight crash, due to CG too far aft.

No one believes the theory except the one who developed it. Everyone believes the experiment except the one who ran it.
STF

 

[TehMightyEngineer]

That makes a lot of sense Spar.

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

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