
Ethiopian Max Crash Simulator Scenario Stuns Pilots - inferiorhuman
https://aviationweek.com/commercial-aviation/ethiopian-max-crash-simulator-scenario-stuns-pilots
======
mcyukon
"WASHINGTON—A simulator session flown by a U.S.-based Boeing 737 MAX crew that
mimicked a key portion of the Ethiopian Airlines Flight 302 (ET302) accident
sequence suggests that the Ethiopian crew faced a near-impossible task of
getting their 737 MAX 8 back under control, and underscores the importance of
pilots understanding severe runaway trim recovery procedures.

Details of the session, shared with Aviation Week, were flown voluntarily as
part of routine, recurrent training. Its purpose: practice recovering from a
scenario in which the aircraft was out of trim and wanting to descend while
flying at a high rate of speed. This is what the ET302 crew faced when it
toggled cutout switches to de-power the MAX’s automatic stabilizer trim motor,
disabling the maneuvering characteristics augmentation system (MCAS) that was
erroneously trimming the horizontal stabilizer nose-down.

In such a scenario, once the trim motor is de-powered, the pilots must use the
hand-operated manual trim wheels to adjust the stabilizers. But they also must
keep the aircraft from descending by pulling back on the control columns to
deflect the elevator portions of the stabilizer upward. Aerodynamic forces
from the nose-up elevator deflection make the entire stabilizer more difficult
to move, and higher airspeed exacerbates the issue.

The U.S. crew tested this by setting up a 737-Next Generation simulator at
10,000 ft., 250 kt. and 2 deg. nose up stabilizer trim. This is slightly
higher altitude but otherwise similar to what the ET302 crew faced as it de-
powered the trim motors 3 min. into the 6 min. flight, and about 1 min. after
the first uncommanded MCAS input. Leading up to the scenario, the Ethiopian
crew used column-mounted manual electric trim to counter some of the MCAS
inputs, but did not get the aircraft back to level trim, as the 737 manual
instructs before de-powering the stabilizer trim motor. The crew also did not
reduce their unusually high speed.

What the U.S. crew found was eye-opening. Keeping the aircraft level required
significant aft-column pressure by the captain, and aerodynamic forces
prevented the first officer from moving the trim wheel a full turn. They
resorted to a little-known procedure to regain control.

The crew repeatedly executed a three-step process known as the roller coaster.
First, let the aircraft’s nose drop, removing elevator nose-down force.
Second, crank the trim wheel, inputting nose-up stabilizer, as the aircraft
descends. Third, pull back on the yokes to raise the nose and slow the
descent. The excessive descent rates during the first two steps meant the crew
got as low as 2,000 ft. during the recovery.

The Ethiopian Ministry of Transport preliminary report on the Mar. 10 ET302
accident suggests the crew attempted to use manual trim after de-powering the
stabilizer motors, but determined it “was not working,” the report said. A
constant trust setting at 94% N1 meant ET302’s airspeed increased to the 737
MAX’s maximum (Vmo), 340 kt., soon after the stabilizer trim motors were cut
off, and did not drop below that level for the remainder of the flight. The
pilots, struggling to keep the aircraft from descending, also maintained
steady to strong aft control-column inputs from the time MCAS first fired
through the end of the flight.

The U.S. crew’s session and a video posted recently by YouTube’s Mentour Pilot
that shows a similar scenario inside a simulator suggest that the resulting
forces on ET302’s stabilizer would have made it nearly impossible to move by
hand.

Neither the current 737 flight manual nor any MCAS-related guidance issued by
Boeing in the wake of the October 2018 crash of Lion Air Flight 610 (JT610),
when MCAS first came to light for most pilots, discuss the roller-coaster
procedure for recovering from severe out-of-trim conditions. The 737 manual
explains that “effort required to manually rotate the stabilizer trim wheels
may be higher under certain flight conditions,” but does not provide details.

The pilot who shared the scenario said he learned the roller coaster procedure
from excerpts of a 737-200 manual posted in an online pilot forum in the wake
of the MAX accidents. It is not taught at his airline.

Boeing’s assumption was that erroneous stabilizer nose-down inputs by MCAS,
such as those experienced by both the JT610 and ET302 crews, would be
diagnosed as runaway stabilizer. The checklist to counter runaway stabilizer
includes using the cutout switches to de-power the stabilizer trim motor. The
ET302 crew followed this, but not until the aircraft was severely out of trim
following the MCAS inputs triggered by faulty angle-of-attack (AOA) data that
told the system the aircraft’s nose was too high.

Unable to move the stabilizer manually, the ET302 crew moved the cutout
switches to power the stabilizer trim motors—something the runaway stabilizer
checklist states should not be done. While this enabled their column-mounted
electric trim input switches, it also re-activated MCAS, which again received
the faulty AOA data and trimmed the stabilizer nose down, leading to a fatal
dive.

The simulator session underscored the importance of reacting quickly to
uncommanded stabilizer movements and avoiding a severe out-of-trim condition,
one of the pilots involved said. “I don’t think the situation would be
survivable at 350 kt. and below 5,000 ft,” this pilot noted.

The ET302 crew climbed through 5,000 ft. shortly after de-powering the trim
motors, and got to about 8,000 ft.—the same amount of altitude the U.S. crew
used up during the roller-coaster maneuvers—before the final dive. A second
pilot not involved in the session but who reviewed the scenario’s details said
it highlighted several training opportunities.

“This is the sort of simulator experience airline crews need to gain an
understanding of how runaway trim can make the aircraft very difficult to
control, and how important it is to rehearse use of manual trim inputs,” this
pilot said.

While Boeing’s runaway stabilizer checklist does not specify it, the second
pilot recommended a maximum thrust of 75% N1 and a 4 deg. nose-up pitch to
keep airspeed under control.

Boeing is developing modifications to MCAS, as well as additional training.
Simulator sessions are expected to be integrated into recurrent training, and
may be required by some regulators, and opted for by some airlines, before
pilots are cleared to fly MAXs again. The MAX fleet has been grounded since
mid-March, a direct result of the two accidents."

------
zaroth
I made the prediction a month ago and I’ll make it again. MCAS won’t ever fly
again.

I think the plane will fly without MCAS with a new type rating, and where
pilots specifically train on the stick feel during a power on stall.

They needed the 737 with new engines to fly like the old 737 in order to
maintain the type rating and avoid training. Now that they obviously have lost
that and require substantial training, I don’t see any reason to keep the
system.

Some people think the plane is unflyable / inherently unstable without MCAS.
I’ve only flown about 15 hours in my life, and a Cessna at that so I’m not
qualified to offer an expert opinion.

But my intuition is that if that were true, if MCAS was not just a bandaid to
maintain a type rating, but rather a safety critical system essential for
flightworthiness, it would never have shipped in its current form in the first
place. Or rather, the 737 MAX would not have been viable to begin with.

If it is the case that 737 MAX is not actually airworthy without a functioning
MCAS then Boeing has fucked up an order of magnitude worse than even they
appear to have at this point.

~~~
janoc
MCAS is not there because of maintaining pilot type rating.

The plane's airworthiness certificate depends on certain behavior while
approaching stall and the new larger and more forward engines on the MAX
changed the behavior of the machine in such way that would make it very
difficult for the crew to bring the nose down at high angles of attack and
high thrust.

The engines on the MAX are forward of the CoG, so they are pushing the nose up
as you add thrust - exactly what you _do not_ want when approach a stall. MCAS
has been added to help with this - to help the crew push the nose down in such
situation by using the stabilizer trim.

The older NG doesn't have this issue because the engines are both smaller and
more to the back, so the pitch-up moment is smaller, even though it is still
present. This is an inherent issue with underslung engines, all planes with
engines mounted under and ahead of the CoG have this issue.

>If it is the case that 737 MAX is not actually airworthy without a
functioning MCAS then Boeing has fucked up an order of magnitude worse than
even they appear to have at this point.

That's BS. By that logic no Airbus or any fly-by-wire plane could ever be
certified - they actually require the computer augmentations to fly. Even the
737 NG has a similar trim system that automatically trims the plane depending
on speed, angle of attack and what not.

~~~
lutorm
_The engines on the MAX are forward of the CoG, so they are pushing the nose
up as you add thrust - exactly what you do not want when approach a stall.
MCAS has been added to help with this - to help the crew push the nose down in
such situation by using the stabilizer trim._

The forward-backward position of the engines have nothing to do with their
resultand pitch torque. What matters is that they are _below_ the CG.

The engines being forward matters because it shifts the center of pressure
forward, giving an inherent pitch-up tendency that becomes more pronounced at
high angles of attack.

And like you say, all planes with underslung engines have this issue to some
degree. Maybe the issue with the MAX is severe enough to cause certification
problems but the stall recovery procedures for the NG apparently already call
for reducing pitch angle before going to full power or you may not be able to
get it down.

~~~
mannykannot
The fore/aft position has a lot to do with the AofA-dependent effect, as it
results from the approximately cylindrical engine nacelles producing some lift
when their axis is at a positive angle of attack (fuselages have a similar
effect [1].) On airplanes with rear-mounted engines, this effect on their
nacelles increases the longitudinal stability [2].

The high/low position matters for the power-dependent effect, and furthermore,
what matters in steady-state is the pitch moment created by misalignment of
thrust and drag (when accelerating, the moment around the CofG also matters.)
A modest tendency to pitch down when the power is reduced is preferable to the
opposite.

The issue MCAS was supposed to solve was due to the AofA-dependent effect.
That's why it has AofA as an input, and not any measurement or proxy for
thrust.

[1] [https://leehamnews.com/2018/11/30/bjorns-corner-pitch-
stabil...](https://leehamnews.com/2018/11/30/bjorns-corner-pitch-stability-
part-2/)

[2] [https://leehamnews.com/2018/12/07/bjorns-corner-pitch-
stabil...](https://leehamnews.com/2018/12/07/bjorns-corner-pitch-stability-
part-3/)

~~~
lutorm
Isn't that exactly what I said? Edit: not quite, good point about center of
drag in steady state conditions.

~~~
mannykannot
"The forward-backward position of the engines have nothing to do with their
resultand pitch torque. What matters is that they are below the CG.

"The engines being forward matters because..."

Janoc repeated a mistake that has been made several times, attributing the
problematic pitch-up to the thrust of low-slung engines, and also made some
mistakes about how that effect works. I am sure you did not intend it, but by
combining corrections to both the former and the latter, and not
differentiating between the two, you ended up with something quite confusing,
so I felt some clarification would help. The key points are that the engines
do produce lift at high AofA, and it is this, not thrust, that creates the
problem MCAS was intended to fix.

~~~
lutorm
_The key points are that the engines do produce lift at high AofA, and it is
this, not thrust, that creates the problem MCAS was intended to fix._

Is that really true? I agree that the pitch-up torque from engine thrust does
not vary based on AoA, but the elevator deflection needed to counteract said
torque definitely depends on airspeed and hence on AoA. Even if there was no
aerodynamic effect of the engines at all, the pilot would be required to trim
nose-down as airspeed goes down relative to an airplane with centerline
thrust.

If the thrust gets high enough, at some point this pitch torque would
overwhelm the natural tendency of the airplane to pitch down as airspeed goes
down and result in negative longitudinal stability.

My impression is that MCAS was intended to counteract the decreasing stick
force with decreasing airspeed. Both effects, offcenter thrust and
aerodynamics, combine to produce the same effect.

~~~
mannykannot
First you said I was repeating what you said, now you are saying the opposite?

Various good sources [1],[2] state that the issue is lift, not thrust. The
article I linked to from my earlier post shows that this lift is not unique to
737 Maxes, and that it contributes to the stability of the DC-9, on account of
being behind the CofG on that airplane.

The LEAP-1B engines of the Max variants are not significantly more powerful
than those on NGs (they are more efficient and somewhat quieter.) As the whole
problem arises from the fact that they cannot be mounted lower, it seems
unlikely that an increased thrust moment is what is making the Max handling
unacceptable.

> If the thrust gets high enough, at some point this pitch torque would
> overwhelm the natural tendency of the airplane to pitch down as airspeed
> goes down and result in negative longitudinal stability.

There seems to be some confusion here over what longitudinal static stability
is: it a matter of the rate of change of pitching moment with respect to AofA
(take a look at the links in my first post for data from real airliners, where
a negative slope indicates stability.) Thrust is not a function of AofA, and
consequently is not factor in the relationship that gives longitudinal
stability of ordinary airplanes - and, as I said before, neither thrust nor
any proxy for it is an input to MCAS (while AofA is.)

[1] [http://www.b737.org.uk/mcas.htm](http://www.b737.org.uk/mcas.htm)

[2] [https://leehamnews.com/2018/11/14/boeings-automatic-trim-
for...](https://leehamnews.com/2018/11/14/boeings-automatic-trim-for-
the-737-max-was-not-disclosed-to-the-pilots/)

~~~
lutorm
Sorry for making unclear references. My question was referring to "it is
[lift], not thrust, that creates the problem MCAS was intended to fix", which
I never addressed before.

The article you linked has some nice cross-sectional illustrations that makes
clear that the thrust line of the MAX engine actually is _higher_ than on the
NG. I hadn't realized this but it makes sense given their larger diameter and
needed ground clearance. That would indicate that the thrust dependent pitch
up is likely smaller on the MAX than the NG so, if the MAX behaves worse, it
stands to reason that the aerodynamic effect must dominate.

I guess the issue is that lift overall is just so much larger that a small
shift in the center of lift has a large effect on pitch moment?

As for your comment about longitudinal stability, I agree that the pitch
moment due to thrust is independent of AoA and hence can't change the shape of
the pitch moment curve. I gotta think about this some more.

------
danols
I am not very concerned with this particular problem anymore since it will get
a satisfactory solution due to its publicity.

What I am worried about and think should get more focus is other potential
issues and corners that has been cut by the Boeing management. I have note
read a single thing that Boeing has handled well in this massive disaster.
This lack of judgement, short term profit seeking & cover up mentality is what
media should spend more time on. It feels to me that they used up a lot of
their trust capital to be allowed to perform any type of self-certification

~~~
adreamingsoul
That is also expected in our Capitalistic system. Greed, profit, and share-
holder value is often more important then the end-user.

Boeing is not the only company that subscribes to that religion.

~~~
akgerber
Rushing to execute a contract in order to meet economic goals is unfortunately
also a failure of nominally-socialist systems:
[https://en.wikipedia.org/wiki/LOT_Polish_Airlines_Flight_505...](https://en.wikipedia.org/wiki/LOT_Polish_Airlines_Flight_5055#Cause)

As are arbitrary cost-cutting goals:
[https://en.wikipedia.org/wiki/LOT_Polish_Airlines_Flight_7#C...](https://en.wikipedia.org/wiki/LOT_Polish_Airlines_Flight_7#Causes_of_disaster)

(I only know about these specific disasters due to reading about the Il-62
because it looks cool)

~~~
beat
More to the point, rushing execution in order to meet economic promises, and
arbitrary cost-cutting, are symptoms of _large_ systems. Capitalist,
socialist, same diff, when it comes to the behavior of bureaucracies.

~~~
mcguire
I don't even know about that. Isn't rushing execution a defining
characteristic of small start up culture?

------
theclaw
> The U.S. crew tested this by setting up a 737-Next Generation simulator at
> 10,000 ft., 250 kt. and 2 deg. nose up stabilizer trim. This is slightly
> higher altitude but otherwise similar to what the ET302 crew faced as it de-
> powered the trim motors 3 min. into the 6 min. flight, and about 1 min.
> after the first uncommanded MCAS input

That's not slightly higher, that's a lot higher. The graphs in the preliminary
report [0] note that the flight _starts_ at around 7,500 ft. since Addis Ababa
Bole International Airport is 7,625 ft. above sea level [1]. Their radar
altitude "about 1 min. after the first uncommanded MCAS input" was ~1,000 ft.
The highest they got above ground was around 6,500 ft. around 5 mins 30
seconds into the flight.

> The excessive descent rates during the first two steps meant the crew got as
> low as 2,000 ft. during the recovery.

If you assume they meant they were 10,000 ft. _above sea level_ in the first
quote, then this quote means they'd be 5,625 ft. under ground at their lowest
point.

[0]
[http://www.ecaa.gov.et/documents/20435/0/Preliminary+Report+...](http://www.ecaa.gov.et/documents/20435/0/Preliminary+Report+B737-800MAX+%2C%28ET-
AVJ%29.pdf)

[1]
[https://en.wikipedia.org/wiki/Addis_Ababa_Bole_International...](https://en.wikipedia.org/wiki/Addis_Ababa_Bole_International_Airport)

edit: oops, refs.

~~~
erentz
So if you run into this problem at 7,500’ above ground level you might just be
okay.

This is why having the ability to disable MCAS without disabling electric
assisted trim is so important and such a big factor in this accident.
Additionally its raised another possible accident scenario:

The runaway trim cutouts were put in place after electric trim in case the
switch (or some other aspect of the electric trim) got stuck in an on position
that would cause the trim to go to full deflection one direction or the other,
hence runaway trim. And hence if you notice this happening you cutout the
power to the electric trim completely.

But now we know you can’t manually trim the aircraft above certain speeds with
some trim levels. Should there be an expectation you can? What if runaway trim
happens and ran to full deflection before a pilot cut it out. That would be
equivalent to the same conditions experienced in this accident - the pilots
now needing to manually trim but being unable to.

So on top of needing separate cutouts for the MCAS and electric trim, should
the manual trim not be investigated for installing some higher ratio
gearing/pulleys to enable over coming the forces experienced here?

~~~
Gibbon1
There is the manual trim as a backup, but it's mechanical advantage is
inadequate when the trim is too far out.

~~~
erentz
Right, which is why I'm saying that means there's been a failure scenario that
existed even _prior to MCAS_. This is how they have demo'd the problem in some
flight simulators for this. The electric trim can without MCAS erroneously
drive the trim into this situation before being cut out. This is why the
cutout switches were put in place decades ago. If this happens in some
situations it could leaving the plane in a position where the trim couldn't be
manually adjusted due to forces. We now know this situation also exists. Is it
so rare, or resolvable in other ways, so it shouldn't be addressed? Or does
there also need to be a fix for the manual trim by adjusting the gear/pulley
ratio such that the pilot could overcome these forces?

~~~
Gibbon1
What I read and makes sense the way to adjust the manual trim if the force on
the stabilizer is too high is to push the nose down to unload it and crank on
the wheel. Probably when this was needed the pilots killed the electric trim
long before it got too far out.

So I agree the manual trim has always been kinda scketch.

------
bengoodger
Is anyone concerned that even in the face of re-training, that two aircraft
could find themselves in this position within the first year of operations?

Let's say you were on one of these aircraft and the pilots were able to
recover. How terrifying would that be? This is the designed behavior?

------
Merrill
Besides retraining, it seems that there must be upper-body strength tests that
737 MAX pilots will have to pass to ensure that they will be able to manually
trim the stabilizer.

Are such tests part of flight crew physicals?

~~~
wyldfire
Poe's law 'n all that -- are you serious? I mean, yes, I've seen the video,
but presumably it won't be safe to require pilots to execute the manual trim,
yeah? IMO either the design is unsafe and must change or there exists a way to
safely fly without ever needing manual trim.

~~~
Merrill
I'm serious. If the final backup system is to revert to mechanical cranks,
pulleys, and cables to move the horizontal stabilizer, then the pilots have to
be able to exert sufficient torque and power on the control wheels to do so.

------
Animats
The 777 and 787 are full fly by wire. The control system has all the sensor
inputs, all the actuator outputs, and a model of how the aircraft is supposed
to behave. If the aircraft isn't doing what's expected, the flight control
system will fault and drop to a dumber control mode, giving the pilot more
control rather than driving control surfaces to their limits trying to correct
the wrong problem. Those systems are managing trim, like MCAS, plus a lot
more.[1]

MCAS is dumb. It has few inputs and one output. It has no overall model of
aircraft behavior. It just detects a bad angle of attack and cranks the trim
to bring the nose down.

The 777 is supposed to handle like a 737. The cockpit controls are reasonably
similar, although different enough that transition training is required.
Unfortunately, there's no "small 777", a gap in Boeing's product line the 737
Max was supposed to fill. (Or small 757, 767, or 787 variants. How did they go
half a century without a new sub-200 seat aircraft?)

[1] [https://www.linkedin.com/pulse/analysis-boeing-777-fly-by-
wi...](https://www.linkedin.com/pulse/analysis-boeing-777-fly-by-wire-system-
jaime-beneyto-g%C3%B3mez-de-barreda)

------
uxhacker
Link to the forum post explaining how to execute the yo-yo manoeuvre,
mentioned in the article. What is interesting was one pilot mentioned that the
yo-yo procedure dates all the way back to the 707 for a runaway trim. The 737
was derived from the 707 and 727. The 707 was the first Jet Airliner.

Edited for links : referance to 737-200 Manuel [https://www.pprune.org/tech-
log/619326-boeing-advice-aerodyn...](https://www.pprune.org/tech-
log/619326-boeing-advice-aerodynamically-relieving-airloads-using-manual-
stabilizer-trim.html#post10414805)

[https://www.pprune.org/tech-log/619326-boeing-advice-
aerodyn...](https://www.pprune.org/tech-log/619326-boeing-advice-
aerodynamically-relieving-airloads-using-manual-stabilizer-trim.html)

~~~
dingaling
The 707 is interesting as the UK air Registration Board refused to certify it
in its original form. It had insufficient rudder authority in the case of
certain engine-out scenarios because Boeing hadn't implemented full rudder
boost, and the pilots therefore couldn't overcome yaw. That had killed two
crews in training. In order to save the big BOAC order Boeing had to fit full
boost and a tail strake, which they quietly adopted for all subsequent 707s

Then there was the 727 that had four fatal crashes within six months of
entering service, which was put down to inadequate training. But it was later
found that the high fatality rate was because Boeing had routed fuel lines
along the belly, which severed in a hard landing and caused immediate fires.
And they severed easily because bizarrely they were aluminium, in order to
bring the weight within target...

------
mimixco
You can watch the simulation in this video by 60 Minutes Australia:

[https://m.youtube.com/watch?feature=youtu.be&v=QytfYyHmxtc](https://m.youtube.com/watch?feature=youtu.be&v=QytfYyHmxtc)

~~~
rasz
do you mean this?
[https://youtu.be/aoNOVlxJmow?t=11m59s](https://youtu.be/aoNOVlxJmow?t=11m59s)

------
bayareanative
This focus on MCAS only is tantamount to a red-herring because there are many
more changes to the 737 NG and MAX that the FAA allowed with little or no
oversight. The absurdly-crude Ducommun critical structural parts debacle
gained almost no media attention in 2010, and several people have died due to
fuselages breaking-up in runway overruns and hard landings where previous and
similar aircraft maintained fuselage integrity. 737 NG, MAX, 787 and all other
Boeing aircraft developed in the past 25 years need to be seriously reexamined
for safety risks and deficiencies.

------
corey_moncure
Kind of sad that they don't report AGL or AMSL along with the elevations here.
How is anyone supposed to make sense of this reporting?

------
fujitzu
TLDR;

1: multi billion dollar U.S. aviation company that employs thousands of
employees statewide screws up

2: the aviation company offers to send consultants to "help" investigate the
cause of the crash, and not falsify or change the narrative of the story in of
the African operated flight whatsoever

3: the reputable Airlines that used their plane, decided to do their own
untampered investigation and found the aviation company at fault

4: leaks get out via a few ethical employees at the aviation company that the
plane was not tested properly and was rushed to market to compete with a rival
European aviation company

5: CEO semi apologizes and the company has nightmare of pr

------
VBprogrammer
One thing I don't understand is how the pilots can override the operation of
the electric trim system by holding the manual trim wheels and yet the
electric trim appears to be able to overcome airloads on the jackscrew that
the pilots can't.

In light aircraft the design of autopilot servos normally includes a clutch so
that the pilot can override the servos. But that limits the force that the
servo can apply.

I guess it could have some kind of torsion sensing system which cuts the power
to the trim motor but I've been unable to find this detailed anywhere.

~~~
janoc
Well, the "Stabilizer wheel - grasp and hold" item of the procedure doesn't
necessarily mean the crew will be able to override it. That's the last ditch
option on the checklist, when everything else has failed, even turning the
motors off (there could be e.g. a short circuit powering the motor).

There is no clutch on the 737, AFAIK, because the forces are such that it
wouldn't work.

Here is a good video by an actual 737 captain explaining how the runaway stab
trim procedure works and what you have to do.
[https://www.youtube.com/watch?v=xixM_cwSLcQ](https://www.youtube.com/watch?v=xixM_cwSLcQ)

And this simulator video shows both how the 737 horizontal stabilizer is
controlled and what kind of forces are on the trim wheel and control column
when severely out of trim:

[https://www.youtube.com/watch?v=aoNOVlxJmow](https://www.youtube.com/watch?v=aoNOVlxJmow)

Should give you an idea what were the Ethiopian pilots facing when unable to
use the electric trim, plane trimmed nose heavy by MCAS and at high speed ...

------
bayareanative
Mentour Pilot's channel:

[https://www.youtube.com/channel/UCwpHKudUkP5tNgmMdexB3ow](https://www.youtube.com/channel/UCwpHKudUkP5tNgmMdexB3ow)

------
fulafel
How do these simulators work? What is the underlying model that gives sim
users assurance that the simulated behaviour corresponds to real world
aerodynamics and eg engine behaviour?

~~~
QuotedForTruth
There are several levels of "Full Flight Simulators" [1] defined by the FAA:
"There are currently four levels of full flight simulator, levels A - D, level
D being the highest standard and being eligible for zero flight time (ZFT)
training of civil pilots when converting from one airliner type to another."

The requirements and process for testing simulators for certification is
documented as well [2]. Its not clear from the article exactly what simulator
they were using though.

[1]
[https://en.wikipedia.org/wiki/Full_flight_simulator](https://en.wikipedia.org/wiki/Full_flight_simulator)

[2]
[https://www.faa.gov/about/initiatives/nsp/media/14CFR60_Sear...](https://www.faa.gov/about/initiatives/nsp/media/14CFR60_Searchable_Version.pdf)

------
mtw
What does this mean for Boeing's responsibility? Is there a case that they
were negligent for this plane and partially responsible for the crash?

~~~
mcguire
This is all largely irrelevant until the actual accident reports are finished.

Yes, it's possible that Boeing will be partially (or even fully, although I
doubt it) responsible.

------
wiremine
This is slightly off topic, but I read write ups like this and wonder how
flight simulators like this work. Do they have to program in the details of
the accident, or is it just a standard Max 737 simulator?

~~~
tk75x
In flight simulators, every aspect of the environment is able to be controlled
by the user. Programming in the details of the accident involves setting up
the same conditions as were present during the accident including altitude,
airspeed, etc. Then the user/instructor would activate specific malfunctions
that will cause the plane to behave like it did during the accident. Now the
pilot is, for all intents and purposes, flying the same plane in the same
conditions that the pilots were during the accident.

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argc
Would a possible recovery method be to roll the plane somewhat so that when
the nose is forced down, it doesn't take the plane directly toward the ground?

~~~
pjc50
You'd need to turn it all the way over, which is likely to upset the
passengers.

~~~
lutorm
Well, I'm sure they'd prefer being upset over being dead... although the
likelihood of successfully rolling over and flying a negative-g recovery in a
transport airplane seem dubious at best. Transport category airplanes are only
certified to -1G so an inverted pullout would definitely exceed those limits.

~~~
rqqt
See Boeing 707 barrel roll by Tex JohnSton.

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virtuexru
Article is behind a paywall unfortunately. Any help? :)

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simcop2387
Found a forum thread about it from some aviation enthusiasts [1]. Some choice
excerpts they made:

‘A simulator session flown by a U.S.-based Boeing 737 MAX crew that mimicked a
key portion of the Flight 302 accident sequence suggests that the crew faced a
near-impossible task of getting their 737 MAX back under control, and
underscores the importance of pilots understanding severe runaway trim
recovery procedures.’

‘What the U.S. crew found -. Keeping the aircraft level required significant
aft-column pressure by the captain, and aerodynamic forces prevented the first
officer from moving the trim wheel a full turn. They resorted to a little-
known procedure to regain control.’ (YoYo Roller Coaster)

The excessive descent rates during the first two steps meant the crew got as
low as 2,000 ft. during the recovery.

...

‘The simulator session underscored the importance of reacting quickly to
uncommanded stabilizer movements and avoiding a severe out-of-trim condition,
one of the pilots involved said. “I donʼt think the situation would be
survivable at 350 kt. and below 5,000 ft,” this pilot noted.’

“This is the sort of simulator experience airline crews need to gain an
understanding of how runaway trim can make the aircraft very difficult to
control, and how important it is to rehearse use of manual trim inputs,”

[1] [https://www.pprune.org/rumours-news/621478-ethiopian-max-
cra...](https://www.pprune.org/rumours-news/621478-ethiopian-max-crash-
simulator-scenario-stuns-pilots.html)

~~~
debt
Can someone shed light on what the "little-known procedure" is they're
referring to?

~~~
theclaw
It's a "roller coaster" procedure where the plane is pitched down to lessen
aerodynamic forces on the stabiliser, allowing the trim wheels to be manually
turned, then pitched up to regain altitude. The process is repeated as
necessary until the trim wheels can be manually moved without it.

~~~
AYBABTME
Interesting, it seems similar to how large sailboats need to head into or down
wind when attempting to trim sails in some conditions? (to reduce pressure on
the sails to allow trimming to be doable by hand)

~~~
Zeebrommer
Yeah, with the important difference that in sailing you lose speed (and heel)
when heading into the wind, whereas a plane will go even faster towards the
ground... Scary!

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tus87
> and underscores the importance of pilots understanding severe runaway trim
> recovery procedures.

So we're back to blaming the pilots?

~~~
daveguy
That's pretty much the opposite, right? That the pilots would need to know an
extreme emergency procedure. In other words you'd need a Sully level pilot to
survive (and unsurvivable below a certain speed and height). If you ask me
that's a damning indictment when a flawed autopilot results in a state like
that.

~~~
namirez
Except Sully actually screwed up and put the passengers life in danger by
trying to land on water and rather than returning to the airport.
[https://www.cbsnews.com/news/ntsb-sully-could-have-made-
it-b...](https://www.cbsnews.com/news/ntsb-sully-could-have-made-it-back-to-
laguardia/)

~~~
Someone1234
This was disproven. And is a major plot point in the movie about Flight 1549
(Sully).

From Wikipedia:

> The NTSB used flight simulators to test the possibility that the flight
> could have returned safely to LaGuardia or diverted to Teterboro; only seven
> of the thirteen simulated returns to La Guardia succeeded, and only one of
> the two to Teterboro.

> Furthermore, the NTSB report called these simulations unrealistic: "The
> immediate turn made by the pilots during the simulations did not reflect or
> account for real-world considerations, such as the time delay required to
> recognize the bird strike and decide on a course of action." A further
> simulation, in which a 35-second delay was inserted to allow for those,
> crashed.

