Indonesian aircraft missing off Jakarta

[Mad (Flt) Scientist]

Originally Posted by GarageYears

Ha! I think you hit the nail on the head with your first sentence. Except it should be re-written to read: "Boeing may have the ONLY simulator with MCAS functions in Seattle".

I doubt that the simulators produced by TRU and CAE have any modeling of the MCAS functionality, and even if they do, I doubly doubt there is a malfunction that allows a single AOA probe failure and corresponding cascading effects.

-GY

MCAS is active during stall-type conditions. Sim qualification includes modelling and matching stalls. So I would expect all sims to include the relevant effects. (But perhaps modelled as a bit of a "black box" rather than with the actual software function on the aircraft.)

What they almost certainly don't have is, as you say, the ability to run specific engineering failure cases.

[climber314]

I forget where I read it (might have been on Twitter) but the news article stated Lion Air pilots have "begun training on Airspeed Disagree and Runaway Stabilizer." No mention of MCAS training. This leads me to believe the current simulators need some updates? I was NOT surprised by this.

Sorry I do not have a source for that.

[tdracer]

Originally Posted by silverstrata

The -400 had 24,000 lb thrust.
The -800 had 27,000 lb thrust.
The max-8 has 28,000 lb thrust.

I call that a steady increase in thrust, with a steady increase in pitch up moment, when applying full power at low speeds. Besides, the Bournemouth incident, where a 737 pitched up to 47 degrees, demonstrated that even the NG series had more thrust-pitch moment than the elevator had aerodynamic pitch moment, when at slow speeds.

Silver

Those numbers are for "Sea Level Static" thrust. Thrust in-flight is different. On large turbofan engines, the net thrust 'lapses' (decreases) with forward speed - the higher the bypass ratio, the greater the lapse with speed (very basically, the ram drag on the inlet goes up faster than the gross thrust generated by the fan exhaust).
I don't have any specific information for the MAX, but I suspect you'd find that, because of the much higher bypass ratio on the Leap, at ~250 knots, the net thrust of the NG -800 and MAX -8 are much closer than the SLS thrust.

[silverstrata]

Originally Posted by tdracer

Those numbers are for "Sea Level Static" thrust. Thrust in-flight is different. On large turbofan engines, the net thrust 'lapses' (decreases) with forward speed - the higher the bypass ratio, the greater the lapse with speed (very basically, the ram drag on the inlet goes up faster than the gross thrust generated by the fan exhaust).
I don't have any specific information for the MAX, but I suspect you'd find that, because of the much higher bypass ratio on the Leap, at ~250 knots, the net thrust of the NG -800 and MAX -8 are much closer than the SLS thrust.

The MCAS system was not designed for 250 kts, it was designed for low speed upsets near the stall. And those events normally (but not exclusively) take place near to sea level. So Boeing would certainly have had to take into account the pitching moments caused by those thrust levels. And the Max does indeed have much more thrust than the old -400. And the NG’s thrust can indeed overpower the elevator, as has already been demonstrated (with passengers aboeard).

Although it would be interesting to see if anyone tried out an inadvertant MCAS operation at 300 kts at 10,000 ft, to see what would happen.

Silver.

[gearlever]

Originally Posted by silverstrata

Although it would be interesting to see if anyone tried out an inadvertant MCAS operation at 300 kts at 10,000 ft, to see what would happen.

Silver.

No thanks.
Still enjoying life.

[gums]

Salute!

Well, re: simulators and flight tests

Although it would be interesting to see if anyone tried out an inadvertant MCAS operation at 300 kts at 10,000 ft, to see what would happen.
Silver.

We just had the inadvertant MCAS "test" it was called JT610

Unless the sims have actual hardwired or mux bus connections/interfaces between black boxes and simulated sensors, they are not very useful for MCAS training when malfunctions happen
.
I would not trust sim if it "emulated" all the boxes, signals and interfaces in on big computer program. Sure, you could have many components in the configuration that were not actual AoA vanes or pitot tubes or free air temp sensors and so forth. The biggie is how all the components work together physically and electronically exactly as in the criterion system. For example, in the new military systems, the actual fire control computer and multiplex bus are not simulated, they are the real thing! The subsystems hanging on the bus or buses might be a "simulation" of the real deal, and can even be dumb boxes or "rheostats/volume controls/tuning knobs". The main thing is to use the actual interfaces/connections in the architecture. If the subsystem has software to process a signal from a sensor, then it should have the identical code as the real deal.

Jez saying, having flown cosmic sims since 1971.

Gums sends...

[GarageYears]

Originally Posted by gums

Salute!

Well, re: simulators and flight tests


We just had the inadvertant MCAS "test" it was called JT610

Unless the sims have actual hardwired or mux bus connections/interfaces between black boxes and simulated sensors, they are not very useful for MCAS training when malfunctions happen
.
I would not trust sim if it "emulated" all the boxes, signals and interfaces in on big computer program. Sure, you could have many components in the configuration that were not actual AoA vanes or pitot tubes or free air temp sensors and so forth. The biggie is how all the components work together physically and electronically exactly as in the criterion system. For example, in the new military systems, the actual fire control computer and multiplex bus are not simulated, they are the real thing! The subsystems hanging on the bus or buses might be a "simulation" of the real deal, and can even be dumb boxes or "rheostats/volume controls/tuning knobs". The main thing is to use the actual interfaces/connections in the architecture. If the subsystem has software to process a signal from a sensor, then it should have the identical code as the real deal.

Jez saying, having flown cosmic sims since 1971.

Gums sends...

The current breed of simulators for the latest Boeing aircraft (including the MAX) use a binary executable supplied by Boeing, which includes any and all aircraft code for avionics, flight control computers, etc, and engineering models of many of the critical system in a manner that is intended to ensure the simulators produced replicate the aircraft as closely as possible... however malfunctions for sensors or other system components must be 'planned' as part of this binary.

In this case the question is whether the MCAS system is modeled in the simulation binary, and is there a way to replicate the failure of a single AOA sensor in the software load?

I suspect only the owners of the simulators I listed previously and Boeing themselves could answer that.

- GY

[jimtx]

Steep turn?

Originally Posted by silverstrata

The MCAS system was not designed for 250 kts, it was designed for low speed upsets near the stall. And those events normally (but not exclusively) take place near to sea level. So Boeing would certainly have had to take into account the pitching moments caused by those thrust levels. And the Max does indeed have much more thrust than the old -400. And the NG’s thrust can indeed overpower the elevator, as has already been demonstrated (with passengers aboeard).

Although it would be interesting to see if anyone tried out an inadvertant MCAS operation at 300 kts at 10,000 ft, to see what would happen.

Silver.

Wouldn’t a steep turn be done at 250 KIAS? So you bank and yank and all of a sudden you don’t have to yank so hard. Anybody done steep turns in a Max sim?

[gums]

Salute Garage

This is what i was concerned with"

In this case the question is whether the MCAS system is modeled in the simulation binary, and is there a way to replicate the failure of a single AOA sensor in the software load?

- Why "model" the MCAS unless it is code in one of the boxes? Is that what it is? Just a chunk of code someplace that can command the stab to trim to its limits faster than the manual trim wheel can? How does it do that?
- Can you tell the box or chunk of code that the AoA sensor on one side is stuck at 20 deg or close to that?
- Can we "fail" a sensor and see how the system reacts? Did the folks at Boeing do that?

I trust the sim folks to model the aero a lot better than the interconnected subsystem boxes or sensors they create in code. The code can't get wet/hot/cold or have a poor solder connection ( can't find the crash, but cause inmplicated a solder gap on a circuit board.

Gums sends...

[CurtainTwitcher]

Originally Posted by gums

Salute Garage

I trust the sim folks to model the aero a lot better than the interconnected subsystem boxes or sensors they create in code. The code can't get wet/hot/cold or have a poor solder connection ( can't find the crash, but cause inmplicated a solder gap on a circuit board.

Gums sends...

Two very recent accidents attributable to poor solder joints as the initial mechanical cause, leading to subsequent mishandling by the crew. TransAsia Airways Flight 235 (final report) and Indonesia AirAsia Flight 8501 (final report)

[568]

Originally Posted by climber314

Or Boeing has the ONLY simulator with MCAS functions in Seattle?

The investigation will next head to Seattle and the 737-MAX engineering simulator where investigators will attempt to exercises to better understand what happened.

If Boeing didn't think it was important enough to mention MCAS in the QRH, why would they provide the code for it in a multi-million dollar simulator? Textron/TRU has 737 MAX Simulators in Miami as of 4/2017, but I would be shocked if they could replicate this flight. I don't think you get extra play time @ > $1,000/hour?

Boeing only has "M Cab" non motion simulators in the Seattle area (near 3-800 building) unless they are using Alaska airlines simulators.
All the simulators were moved to MIA around the 2013 time frame.

[ontheklacker]

MCAS to me is not a "system" per se, but simply an additional subroutine in the Flight Control Computer. Albeit, a poorly coded one. Most computers attached to flight controls have multiple channels that compare their inputs before making an output. A single faulty AoA sensor activated the MCAS subroutine of the FCC. Flaps up, high AoA (stalling), MCAS commands the existing trim system to trim the nose down until the high AoA indication goes away. A single failure should not have activated this logic. That's why commercial aircraft have at least 2 of everything.

This being said, anyone who has flown a 737 classic / NG / Max knows that commanded or uncommanded trim wheel movement is very noticeable - both thru sight and sound. The crew the day before the mishap flight readily identified the uncommanded movement and completed the QRH. The mishap crew did not. As to why they didn't, hopefully we will find out.

Why is there MCAS software on the Max, maybe the FAA was the driving force. It's interesting that this year the FAA has put high emphasis on full (not stick shaker) stall recovery during AQP. Maybe this is yet another result of the Colgan Air 3407 crash in Buffalo, NY, 2010?

[Roger_Murdock]

Originally Posted by ontheklacker

Maybe this is yet another result of the Colgan Air 3407 crash in Buffalo, NY, 2010?

2009. In fact, the 10 year anniversary is only a couple of months away.

[zzuf]

Originally Posted by ontheklacker

MCAS to me is not a "system" per se, but simply an additional subroutine in the Flight Control Computer. Albeit, a poorly coded one. Most computers attached to flight controls have multiple channels that compare their inputs before making an output. A single faulty AoA sensor activated the MCAS subroutine of the FCC. Flaps up, high AoA (stalling), MCAS commands the existing trim system to trim the nose down until the high AoA indication goes away. A single failure should not have activated this logic. That's why commercial aircraft have at least 2 of everything.

This being said, anyone who has flown a 737 classic / NG / Max knows that commanded or uncommanded trim wheel movement is very noticeable - both thru sight and sound. The crew the day before the mishap flight readily identified the uncommanded movement and completed the QRH. The mishap crew did not. As to why they didn't, hopefully we will find out.

Why is there MCAS software on the Max, maybe the FAA was the driving force. It's interesting that this year the FAA has put high emphasis on full (not stick shaker) stall recovery during AQP. Maybe this is yet another result of the Colgan Air 3407 crash in Buffalo, NY, 2010?

Similar to my thoughts.
The MCAS seems to be a stick nudger with a complicated Boeing name.

Why would the 737 MAX need a stick nudger?

My guess is that during stall testing, and particularly turning flight, flaps up, power on, aft cg, and probably 3kts/second deceleration. The aircraft could not be shown to comply with the longitudinal static stability requirements implied in FAR25.203(a).
This is not common, but not unheard of. A stick nudger seems to be the quick fix.
Nowhere has it been implied that the actual stall characteristics are in question.
The questions about longitudinal control authority are asked in other sections of FAR25.

But stick nudgers are old hat, why not just install a nudger actuator?

The non-compliance with static stability requirements in other areas of the envelope meant the speed trim system was fitted.
It would be almost trivial engineering to add a nudger function to the STS system.
The failure mode and effects analysis was almost already done.
The switchery was in place for the runaway case.
There was already a crew procedure in place for the runaway case.

How could it runaway with just a single AOA signal indicating it was approaching the area of longitudinal instability?

Of course that is the real question.
For the aircraft to "know" it was in a configuration and flight conditions for the MCAS to operate it would seem to require a number of sensor input that were within the trigger range of the MCAS. If any of these signals was missing the false AOA signal should not have caused the MCAS to operate.

That Boeing, FAA, Pilots unions have not called for immediate changes to the MCAS, makes me think there is already more known than is being released publicly.

[CurtainTwitcher]

Originally Posted by ontheklacker

This being said, anyone who has flown a 737 classic / NG / Max knows that commanded or uncommanded trim wheel movement is very noticeable - both thru sight and sound. The crew the day before the mishap flight readily identified the uncommanded movement and completed the QRH. The mishap crew did not. As to why they didn't, hopefully we will find out.

The trim wheel sound would have been inaudible with the stick shaker continuously sounding. Not easy to think or communicate with that continuously sounding. Any attempt to communicate subtleties would have been very difficult.

I can give you a very practical demonstration, the video below is a 5 min loop of the B737 stick shaker (half the flight time of this flight).

put in on, and try to a complex cognitive puzzle task that requires you to solve a problem that no line pilot has ever seen, nor could have reasonably anticipate. Just because other crews succeeded, does prove this is a satisfactory state of affairs for an RPT line flight.

[Rated De]

Originally Posted by CurtainTwitcher

The trim wheel sound would have been inaudible with the stick shaker continuously sounding. Not easy to think or communicate with that continuously sounding. Any attempt to communicate subtleties would have been very difficult.

I can give you a very practical demonstration, the video below is a 5 min loop of the B737 stick shaker (half the flight time of this flight).

put in on, and try to a complex cognitive puzzle task that requires you to solve a problem that no line pilot has ever seen, nor could have reasonably anticipate. Just because other crews succeeded, does prove this is a satisfactory state of affairs for an RPT line flight.

Thank you CT, that is precisely the point.
It is all rather simple after the event.
Imagine being in that environment, an overload of sound, noise and that old primal fear? We do not know exactly what transpired as the two souls who could tell us are no longer here.
What seems to be missed is that the system that kept driving the nose down was a system Boeing decided the pilots did not need to know about.

To borrow from Donald Rumsfeld,

'There are things we know that we know. There are known unknowns. That is to say there are things that we now know we don't know. But there are also unknown unknowns'.

Not having the FDR recorder ought suggest to the astute that there is more that we do not know, that we do not know.

[silverstrata]

Originally Posted by jimtx

Wouldn’t a steep turn be done at 250 KIAS? So you bank and yank and all of a sudden you don’t have to yank so hard. Anybody done steep turns in a Max sim?

A high speed stall is not the same, as the elevator will still have a lot of authority at those higher speeds. MCAS was designed for a slow speed stall, when engine thrust combined with engine aerodynamic pitch-component, could and would exceed elevator authority and send the nose skywards. The MCAS is an anti home-sick-angel device.

The trouble is, as soon as it lowers the nose and gains speed, MCAS turns into a super gravitational attractant. Unless you can take all that forward trim off in a few seconds, your shiny 737 becomes a Stuka in terminaI dive mode. I still have no idea how anyone certified a device that would give a slippery passenger jet, full forward trim. And give that trim, when the aircraft is likely to end up 20 degree pitch down, and gaining speed rapidly.

Especially when the QRH (and I presume the Max QRH) says do not use too much trim in an incipient stall, as the aircraft may become uncontrollable. Actual wording for the approach to stall is:

Excessive use of pitch trim may aggravate the condition, or may result in loss of control, or in high structural loads.

And yet that is exactly what MCAS is giving you. I fail to see how Boeing can dodge this important issue, and not be forced to make major amendments to the MCAS system. At the very least MCAS should stop trimming at a safe point where a recovery from a dive is still possible - say 3-units on the trim indicator....!!

Silver

Edit: As to Zzuf’s question about why not fit a stick-pusher instead, I suspect this was a certification issue. If Boeing had admitted a stick-push was required, then a lot more certification would also have been required. But if you slip in a trim-pusher by the back door, then perhaps nobody will notice....

.

[Hi_Tech]

I am not sure if anyone discussed the following points. Having read through the entire thread (over several weeks), I cannot recollect what has puzzled me a lot with the reporting by crew.
1. The previous sector the Stick-shaker, was continuously working through out the flight.
2. They stopped the Trim actuation (MCAS) by stab cutout switches.
3. They flew the aircraft manually the whole sector.

Why the crew did not write these down in Tech Log. For me with over 40 years as an engineer, this reporting astonishes me. It is not enough if you speak to the guy you meet on arrival of flight. He may not be the guy who really works later on the aircraft in trying to rectify. These are not defects that are just to be passed on verbally, or as just a crew report to operations.
I will mention an instance in my career. The aircraft, a Boeing, experienced pulling to the right during landing roll. The Captain wrote in the Tech Log the defect and a statement "This aircraft is "Un-airworthy' in capitals. What he meant, when I asked him, is that on a wet runway, this aircraft can land in the ditch, as the pulling is severe. He did not have to tell me more.
I am somewhat sure that if the crew had mentioned these 3 defects above in Tech Log, the ill-fated crew on the next flight, might have dealt with the same problem differently. I think. Any comments?

[zzuf]

Originally Posted by silverstrata

Edit: As to Zzuf’s question about why not fit a stick-pusher instead, I suspect this was a certification issue. If Boeing had admitted a stick-push was required, then a lot more certification would also have been required. But if you slip in a trim-pusher by the back door, then perhaps nobody will notice....

That is not a question I asked.
Stick pushers are only fitted when the actual stall characteristics are non-compliant, not for stability issues approaching the stall.
Years ago, instability approaching the stall was acceptable provided a pronounced nose down pitch occurred at the stall.
Some regulatory authorities didn't much like the thought of self stalling aircraft (due lack of longitudinal static stability) so the stability requirements approaching the stall were tightened up, and stick nudgers came into being for those aircraft which couldn't comply.
Not heard any issues about the 737 MAX stall characteristics which would mandate fitting a stick pusher.
Pushing stuff through the "back door" is not how certification works. How do you think the FAA and other regulatory authority test pilots would react when presented with such non-compliances?

[patplan]

Hi_Tech;

Well, #3, flying the plane manually was "given". The aircraft flying with IAS disagree and ALT unreliable will have the autopilot automatically turned-off.

#2 was vaguely described in the log. Not knowing it was MCAS [or even its existence] doing its job, they thought it was a malfunctioning STS going the wrong way due to speed difference, so they wrote it that way in there.

#1, on the other hand, the BIG ONE- the stick shaker, their failure to mention it, in the log or to the MX, is likely to become one of the major focus for the investigation.