dragon6172 wrote:

speedking wrote:

Hmm.. You are flying at 2000ft with 400kts. Stick shaker on. Screens lit like a Christmas tree.
MCAS kicks in, plane starts to drop. Column too heavy to hold back with two hands.
Now you need to troubleshoot, make a decision to switch off the trim, take one hand off from the column, reach behind to switch the trim off, start manually rotating the trim while flying with one hand with a column too heavy to hold back.
Is this physically possible? How much time one would have for this before...Boom!
How fast does a plane drop 2000ft if it is flying at 400kts and you push it down?

Or you could use that handy electric trim switch that's right under your thumb on the control column you're pulling so hard on to return the aircraft to a normal trim state before you disable electric trim. As has been pointed out numerous times the pilot ALWAYS has authority over MCAS inputs using the control column electric trim switch.

Ok, of course, got that. Thanks. Hmm.. how you would be able to determine you are actually descending if your speed and AoA readings are faulty in this situation?
And what about the time from 2000ft to ground?

speedking wrote:

dragon6172 wrote:

speedking wrote:

Hmm.. You are flying at 2000ft with 400kts. Stick shaker on. Screens lit like a Christmas tree.
MCAS kicks in, plane starts to drop. Column too heavy to hold back with two hands.
Now you need to troubleshoot, make a decision to switch off the trim, take one hand off from the column, reach behind to switch the trim off, start manually rotating the trim while flying with one hand with a column too heavy to hold back.
Is this physically possible? How much time one would have for this before...Boom!
How fast does a plane drop 2000ft if it is flying at 400kts and you push it down?

Or you could use that handy electric trim switch that's right under your thumb on the control column you're pulling so hard on to return the aircraft to a normal trim state before you disable electric trim. As has been pointed out numerous times the pilot ALWAYS has authority over MCAS inputs using the control column electric trim switch.

Ok, of course, got that. Thanks. Hmm.. how you would be able to determine you are actually descending if your speed and AoA readings are faulty in this situation?
And what about the time from 2000ft to ground?

Seriously? Still have an attitude indicator. Fly pitch and power.

kayik wrote:

dtw2hyd wrote:

...Boeing Defense Systems has vast experience with software to control airframes lacking static stability. Most modern fighter planes are inherently unstable for various reasons. So it is not impossible with just software fix for Boeing. Just tighten the loose ends and make it more intuitive to human pilots...

I am sure they have, as they have experience in building commercial aircraft. What I am saying is, they will eventually fly the grounded aircraft but will they be able sell them anymore and keep their order book intact. We are talking about human passengers at the end.

787 battery still in box, years after ungrounding, one of the fastest selling widebody.
GTF is not in the clear either, A320NEOs have no issues selling.
A lot of Trent powered 787s were AOG, RR still fixing many of them.

Boeing would have no issue selling MAXes.

journeyperson wrote:

dtw2hyd wrote:

kayik wrote:

...
It is not going to be like "we upgraded the software, let's fly". Certification will take ages. Given its credibility, FAA's decision is not enough, European authorities and Asians should be convinced, as well.
.

They have been working on software fix since Nov '18. Boeing Defense Systems has vast experience with software to control airframes lacking static stability. Most modern fighter planes are inherently unstable for various reasons. So it is not impossible with just software fix for Boeing. Just tighten the loose ends and make it more intuitive to human pilots.

I think any reasonable fix will be quickly accepted and frames should flying again very soon. No one wants (or) can afford to keep these grounded for a long time.

There will be a judgment call on the cost of major MAX redesign (vs) clean sheet design. If the redesign costs too much Boeing may roll out the new plane and let customers swap orders.

From parts of the regulations that have been posted in these threads I understand that it is not permissible for a civil airliner to rely on software systems to make it stable in flight. If the 737 MAX relies on such systems to make it stay in the air at any phase of flight it shouldn't have been certificated. I am only going from what I think I have learned here in these threads; correct me if I am wrong.

My understanding is that the software exists to make the MAX behave like an NG. Not because the MAX is unstable per se.

dragon6172 wrote:

speedking wrote:

dragon6172 wrote:

Or you could use that handy electric trim switch that's right under your thumb on the control column you're pulling so hard on to return the aircraft to a normal trim state before you disable electric trim. As has been pointed out numerous times the pilot ALWAYS has authority over MCAS inputs using the control column electric trim switch.

Ok, of course, got that. Thanks. Hmm.. how you would be able to determine you are actually descending if your speed and AoA readings are faulty in this situation?
And what about the time from 2000ft to ground?

Seriously? Still have an attitude indicator. Fly pitch and power.

Let me rephrase my question: If the MCAS activates with maximum (faulty) control at that altitude and speed, how much time one would have to notice and recover?

How fast can you out the windscreen and notice the horizon getting worryingly high up the view? I’d say a couple of seconds.

GF

Sooner787 wrote:

VS11 wrote:

How soon apart were the two crashed MAXes built? Who is the manufacturer of the pitot tubes and the AOA indicators? MCAS may have its issues and like all software it is work in progress - wouldn’t be surprised if Boeing was working on newer versions even before Lion Jet. However, there is this serious issue of low quality components being installed on jets. Does Boeing or Airbus test these component before installed?

That's what I've been wondering. What if this turns out to be a manufacturing quality issue,
perhaps a batch of faulty AOA indicators or heck, maybe some bad wiring installations?

There was plenty of discussion how hard the workers were scrambling to adjust to
the higher build rate at the Renton factory. Something could have fallen thru the cracks
in their rush to catch up to the breakneck build rate

Lion - PK-LQP c/n 43000 l/n 7058 first flight 30-07-18
Ethiopian - ET-AVJ c/n 62450 l/n 7243 first flight 30-10-18

Hi all.. xpert says that When the ethiopian ntsb arrive at the crash site they found the parts of max8 that drive the horizontal Trim mecanism..that parts show the ntsb its final position that can make the plane nose dive (it stuck on that position)... i saw it some kind like dynamo or some thing i forgot the name.. sorry for my english

osiris30 wrote:

Who the hell said anything about disabling auto-pilot? Just auto-trim... Not sure where you are getting this from, did I misword something in my post that has lead you to suggest they turned off the entire AP system? I am merely suggesting someone hit stab cut-off.

How do you think AP works? There is no "disable MCAS" switch. The stab cutout will disable MCAS but it also disables your electric trim (talking about the electric trim operated by the pilots with their thumb on the yoke) and AP itself.

You would be taking off and flying the entire flight without AP and without electric trim, only the manual wheel

osiris30 wrote:

Before you say 'wow that would be so weird I have never heard of it', there was a report in the Nasa database of an AA flight crew doing EXACTLY that, for EXACTLY this reason. (edit: I may be getting the soources or airlines mixed, but it was reported in this thread already, just not going to search for it).

I would have to have more context before commenting, and hey, I could be wrong, yes. But I'd be surprised if this is a normal occurrence by crews on passenger flights day after day condoned by the airline. My AA 737 NG/MAX friend didn't indicate he was doing much different, but that is an anecdote and I didn't really ask too many details

osiris30 wrote:

If you have a better explanation for a lack of climb performance (on take off) than incorrect trim when airspeed is well above what is needed to climb, PLEASE share it.

I don't and that is my point--I don't know why or even if there actually was a lack of climb performance. I don't have a better explanation and I'm not going to pretend I do. I don't think anyone on this forum has one, I don't think most aviation professionals do, I bet even the investigators probably don't have enough knowledge to make a certain assessment

osiris30 wrote:

I don't think anyone is suggesting otherwise. I certainly am not. I agree fully with your last part of the statement (hell I even agree with some of your cautions before that point), not sure why this bit of speculation is the one you chose to single out though where there are 50+ pages of largely speculation here. At least mine I tried to fit the observed paramaters to address the TAKE OFF and INITIAL CLIMB portion of the flight.

I suppose it's a fit, but it's a forced fit IMO, does not seem realistic.

I don't want to appear that I am targeting you, I merely jumped into the discussion around where your post was. I take issue with 1: how certain you sounded in your post, considering how unlikely your scenario sounded based off my, admittedly, light 737 NG piloting (just short of 1000 hours) and 2: the whole notion that we currently need an explanation. Wording like "if you have a better explanation" kinda proves my point... whether or not I have an explanation, a better one, lack of one, educated or non-educated guess, etc is irrelevant to whether yours makes sense. It's perfectly valid of me to sit back without a formed opinion and poke holes in the opinion's of others. If I make a claim, then I'll be required to back it up

Having a hard time wrapping my head around trained pilots not being able to overcome a trim system malfunction to the point that it crashes the plane. The thumb switch is right there. If it keeps working against your wishes, reach down and turn it off. The Lion plane flew relatively straight and level for several minutes doing just that and then ???????? Why did they stop correcting it? This flight, I'm not sure we know enough, other than the jackscrew report, but maybe not enough altitude to counter the trim in time? Question- what kind of dive angle does full down trim produce? It's just trim isn't it? Fine adjustment? We're not talking dive bomber here are we?

GalaxyFlyer wrote:

How fast can you out the windscreen and notice the horizon getting worryingly high up the view? I’d say a couple of seconds.

GF

Yeah, thanks. What I'm looking for is something a bit more scientific. Something like: The trim moves x degrees per sec which causes the plane deviate from the altitude this many ft per sec. If you are busy for something else than looking at the view and don't counteract the MCAS control.

There’s nothing like that. The trim does NOT change the rate of altitude change, pulling on the yoke creates more AOA which creates more lift which changes the rate of descent. The trio moves at .27*/sec on the autopilot or MCAS, something like 1*/sec when the pilot uses the trim. But pull on yoke is first.


GF

speedking wrote:

GalaxyFlyer wrote:

How fast can you out the windscreen and notice the horizon getting worryingly high up the view? I’d say a couple of seconds.

GF

Yeah, thanks. What I'm looking for is something a bit more scientific. Something like: The trim moves x degrees per sec which causes the plane deviate from the altitude this many ft per sec. If you are busy for something else than looking at the view and don't counteract the MCAS control.

MCAS moves the trim around .25 degrees per second for up to 10 seconds at a time. At any time during that 10 second period the pilot can stop the auto trim down with their control column trim switch. Now what that equals in feet per second and time etc depends on a lot of things

At 2G, the turn (pitch change) rate is 6*/second, but if opposing the 1G of level flight, about 4*/second

GF

osiris30 wrote:

If you have a better explanation for a lack of climb performance (on take off) than incorrect trim when airspeed is well above what is needed to climb, PLEASE share it.

I think the easy explanation is they had stick shaker at takeoff and they initially purposely reduced their climb rate to prevent a stall

In post #2411 GalaxyFlyer has a PPW quote about the MAX that caught my eye: "it's another dynamically unstable aircraft". Really? In my corner of the world wings rotate, so in the fixed wing world I'm just an interested bystander. Is the MAX really dynamically unstable, i.e., with eigenvalues in the right-half-plane? I know that this specific information is probably not in the public domain -- in most, if not all, technical presentations by industry all the y-axes are typically without scales -- but anecdotally, from pilots who fly the aircraft. In the rotary-wing world, the ADS-33 handling qualities spec will give you Level 1 HQ if you are unstable (but not for "Divided Attention Operations") but the frequency of oscillation has to be very low and the time-to-double-amplitude very very long. A very slightly unstable phugoid may still be OK. So, a dynamically unstable airliner (with the FCS off) can still be certified? I'm really curious.

^^^ ok so with that info and apparently how easy it is to disable the trim or a failing mcas system due to faulty sensor inputs....how did these pilots allow the plane to fall out of the sky? Some replies I got earlier made it seem like you cannot manually fly the 737max?!? I wish I knew why it was so hard for me to comprehend that the pilots had NO ability to fly this airplane the old stick and rudder way.

speedking wrote:

GalaxyFlyer wrote:

How fast can you out the windscreen and notice the horizon getting worryingly high up the view? I’d say a couple of seconds.

GF

Yeah, thanks. What I'm looking for is something a bit more scientific. Something like: The trim moves x degrees per sec which causes the plane deviate from the altitude this many ft per sec. If you are busy for something else than looking at the view and don't counteract the MCAS control.

We know they tried for several minutes to gain control of the plane.

dragon6172 wrote:

speedking wrote:

GalaxyFlyer wrote:

How fast can you out the windscreen and notice the horizon getting worryingly high up the view? I’d say a couple of seconds.

GF

Yeah, thanks. What I'm looking for is something a bit more scientific. Something like: The trim moves x degrees per sec which causes the plane deviate from the altitude this many ft per sec. If you are busy for something else than looking at the view and don't counteract the MCAS control.

MCAS moves the trim around .25 degrees per second for up to 10 seconds at a time. At any time during that 10 second period the pilot can stop the auto trim down with their control column trim switch. Now what that equals in feet per second and time etc depends on a lot of things

Thanks. Interesting. If I understood correctly, let's say in 5 seconds the trim moves 1.25 deg. Question would be how quickly would the altitude then drop if the plane is flying at 2000ft with a speed of 400kts?
I'm trying to find something tangible to the long discussion of what is expected from the pilots. Like: They had 15.8 sec to recover from the situation but didn't / couldn't do it because of this and that....

trnswrld wrote:

^^^ ok so with that info and apparently how easy it is to disable the trim or a failing mcas system due to faulty sensor inputs....how did these pilots allow the plane to fall out of the sky? Some replies I got earlier made it seem like you cannot manually fly the 737max?!? I wish I knew why it was so hard for me to comprehend that the pilots had NO ability to fly this airplane the old stick and rudder way.

We know that Lion pilots flew successfully flew the accident aircraft with the electric trim disabled, which also means the MCAS is disabled.

I also assume that the plane is controllable without MCAS or autopilot since that is how most takeoffs and landing occur.

From what I understand the 737 max 8 and 9 required this new mcas system because the engine placements would cause the aircraft to always pitch nose up. Why couldn't boeing inform pilots and in the manuals state this particular aircraft has this pitch up tendency and avoid this new mcas like the older 737 NG models? Can't the pilots calculate and configure for this nose up tendency for landings, take offs, and at cruise without the new mcas? Why was the mcas required in the 737 max 8 and 9 when qualified pilots could account for this pitch up trend?

It’s required to meet specific, as in pounds of stick force, at a particular corner of the envelope. A corner that’s is rarely seen in normal flight operations. The “pitch up” is that it, approaching the stall AOA in a clean configuration, the stick force required to continue pitching up becomes very light or even negative, so the plane would almost continue to stall of its own accord.

To the earlier comment, “dynamically unstable” is a comment by a pilot, not an aerodynamic reality or violation of certification criteria. Note, the same was applied to the MD-11.

GF

Previous posters compared MCAS to driver assist features on vehicles. In some cases, even when switched off, or even when fuses are pulled, some of these assist features remain in operation.

Suspect MCAS will be similar. In certain flight conditions, in certain settings, different whether being flown from the left or right seat, whether autopilot on or off, or flaps extended or not, MCAS will intervene. Also, MCAS intervention will turn out not to be as linear or predictable as previously thought.

speedking wrote:

dragon6172 wrote:

speedking wrote:

Yeah, thanks. What I'm looking for is something a bit more scientific. Something like: The trim moves x degrees per sec which causes the plane deviate from the altitude this many ft per sec. If you are busy for something else than looking at the view and don't counteract the MCAS control.

MCAS moves the trim around .25 degrees per second for up to 10 seconds at a time. At any time during that 10 second period the pilot can stop the auto trim down with their control column trim switch. Now what that equals in feet per second and time etc depends on a lot of things

Thanks. Interesting. If I understood correctly, let's say in 5 seconds the trim moves 1.25 deg. Question would be how quickly would the altitude then drop if the plane is flying at 2000ft with a speed of 400kts?
I'm trying to find something tangible to the long discussion of what is expected from the pilots. Like: They had 15.8 sec to recover from the situation but didn't / couldn't do it because of this and that....

Anybody? Let's do some speculations: Descent rate is 8000fpm. From 2000ft you can drop to 1000ft until you need to pull up to prevent a crash. This 1000ft drop would take 7.5sec.
Would it be close if we estimate that the pilots had 5-10sec to realize the MCAS kicked in and respond correctly to save the plane?

How much dive angle? Dive recovery is a turn which depends on G and TAS.

GF

trnswrld wrote:

^^^ ok so with that info and apparently how easy it is to disable the trim or a failing mcas system due to faulty sensor inputs....how did these pilots allow the plane to fall out of the sky? Some replies I got earlier made it seem like you cannot manually fly the 737max?!? I wish I knew why it was so hard for me to comprehend that the pilots had NO ability to fly this airplane the old stick and rudder way.

An AA pilot said that you can turn it off and manually take over the plane. It was in a yahoo.com article I read. He felt the nose dipping and caught it right away. Switched it off and pulled up. The rest of the flight was fine. So in AA's training, his first reaction was correct.

I wonder how many training hours did previous pilot have before each crash? MAX hours, not just 737s.

What if Boeing had informed airlines and pilots from the beginning of MCAS (but left out the non-redundancy issue)? Isn't it obvious to conclude that some of those pilots would want to (in the simulator):
(1) Fly into a stall situation, to 'feel' how MCAS would solve the problem, assisting them with nose down.
(2) Repeat (1) but a low altitude, maybe to determine the minimum altitude to recover from a stall using MCAS
(3) Repeat (2) but without MCAS ("hey you mean I can't do that? without disabling electric stabilizer trim? Oh you want me to take off without electric stabilizer trim!! Let's try it...")
(4) ...
(99) Now stall is dependent on AOA and airspeed sensors, so I want to simulate a bad AOA sensor at 32000 ft. Let's try that... because I'm curious if MCAS is a redundant system and will pick the good sensor.

Isn't this why Boeing didn't tell anybody about MCAS? Because of item (99) above? I mean that's the eventual sim run isn't it??

GalaxyFlyer wrote:

How much dive angle? Dive recovery is a turn which depends on G and TAS.

GF

Good question. How much dive angle you get with for example with a 2.5 deg trim at that speed and altitude? How much was the angle in the last Lion Air dive? Estimated TAS would be 400kts from 2000ft altitude. The math goes beyond my expertise.
Maybe someone with an access to a simulator could shed some light in this?

Thanks for your answers.

Np2019 wrote:

From what I understand the 737 max 8 and 9 required this new mcas system because the engine placements would cause the aircraft to always pitch nose up. Why couldn't boeing inform pilots and in the manuals state this particular aircraft has this pitch up tendency and avoid this new mcas like the older 737 NG models? Can't the pilots calculate and configure for this nose up tendency for landings, take offs, and at cruise without the new mcas? Why was the mcas required in the 737 max 8 and 9 when qualified pilots could account for this pitch up trend?

FAR (federal aviation regulations) require a certain amount of longitudinal stability for certification in all modes (including "manual")

GalaxyFlyer wrote:

How fast can you out the windscreen and notice the horizon getting worryingly high up the view? I’d say a couple of seconds.

GF

Naw it’s not terribly fast. There still isn’t a whole heap of information given to us on the MCAS system, but I’m guessing it’s the same rate as the Speed Trim, which isn’t terribly fast. It’s easily defeated with some nose up trim which then freezes the MCAS for 5 seconds.

hamiltondaniel wrote:

747megatop wrote:

It is as simple as Mercedes, BMW or Toyota putting in a feature where, it accelerates the car when you hit the brake pedal and people arguing that the driver did not have enough experience or should have flipped some switches to disconnect that feature!!!!

That's an interesting parallel you draw, because the final investigation into this issue found that it had nothing to do with the cars, the pedals, or the switches; people were stepping on the wrong pedal (they were hitting the gas instead of the brake). This is actually not a new phenomenon; it happened with Audis in the 1980s, was similarly investigated on technical grounds, and was ultimately revealed to be, yes, people stepping on the wrong pedal.

Malcolm Gladwell actually did a very interesting podcast on the issue, if you're interested. Revisionist History is the name of the podcast, episode called "Blame Game."

So, once again, we don't know what happened on this plane. But your analogy isn't very good evidence for your position. People are more likely to make mistakes than machines.

And AUDIs reputation was damaged due to media hysteria and social pressures. Sound familiar?

In the 2000s there have been real issues with cars on the highway accelerating and losing the brakes. This is only possible because everything is electronic now. The Audis had mechanical throttles and mechanical brakes systems and it was impossible to have the brake pedal make the car go.

But that didnt stop the media...

trnswrld wrote:

^^^ ok so with that info and apparently how easy it is to disable the trim or a failing mcas system due to faulty sensor inputs....how did these pilots allow the plane to fall out of the sky? Some replies I got earlier made it seem like you cannot manually fly the 737max?!? I wish I knew why it was so hard for me to comprehend that the pilots had NO ability to fly this airplane the old stick and rudder way.

Well, we still don’t know if the Ethiopian accident was even an MCAS event. So we don’t know what they were encountering yet. You can most definitely hand fly the MAX. Autopilot off is the first thing to do if the airplane isn’t behaving as it’s supposed to... which is why the Amazon 767 crash is so eye opening. Why was the autopilot engaged all the way to the ground?

dragon6172 wrote:

osiris30 wrote:

If you have a better explanation for a lack of climb performance (on take off) than incorrect trim when airspeed is well above what is needed to climb, PLEASE share it.

I think the easy explanation is they had stick shaker at takeoff and they initially purposely reduced their climb rate to prevent a stall

Doesn't explain the takeoff roll and breakaway speed though (at least to me). If you look at the data it *appears* the nose gear switch triggered at 89kts, meaning the nose was lifted off the runway (or a faulty switch, but damn how many faults can one particular plane have!!!). Then at 160kts they are airborne 'for real', which is a very high speed to finally get off the ground when you've been holding the nose off ostensibly since 89kts.

It is all very strange. Hopefully in a day or two we will get some FDR data. Given the grounding they data is likely to be released quickly, or at least a synopsis of it.

smartplane wrote:

Previous posters compared MCAS to driver assist features on vehicles. In some cases, even when switched off, or even when fuses are pulled, some of these assist features remain in operation.

Suspect MCAS will be similar. In certain flight conditions, in certain settings, different whether being flown from the left or right seat, whether autopilot on or off, or flaps extended or not, MCAS will intervene. Also, MCAS intervention will turn out not to be as linear or predictable as previously thought.

If you disable electric trim MCAS can't operate. MCAS will be predictable. As currently implemented, when it gets bad sensor data it pitches the nose down. If the software engineers at Boeing can't write code to only enable MCAS under certain conditions, how in Earth did they manage to write the code for the 787?

There is no issue with the mcas concept, the issue is that there are no limits or safeguards.

DeltaMD90 wrote:

osiris30 wrote:

Who the hell said anything about disabling auto-pilot? Just auto-trim... Not sure where you are getting this from, did I misword something in my post that has lead you to suggest they turned off the entire AP system? I am merely suggesting someone hit stab cut-off.

How do you think AP works? There is no "disable MCAS" switch. The stab cutout will disable MCAS but it also disables your electric trim (talking about the electric trim operated by the pilots with their thumb on the yoke) and AP itself.

You would be taking off and flying the entire flight without AP and without electric trim, only the manual wheel

As I understand it, stab cut does not disable all AP functionality. I may be wrong, but I am pretty sure the rest (speed hold, nav hold, AT, etc) all still function if you hit the stab cut switched located beneath .. well beside and beneath the trim wheel. Happy to be corrected, but my understanding is it is not all or nothing.

osiris30 wrote:

Before you say 'wow that would be so weird I have never heard of it', there was a report in the Nasa database of an AA flight crew doing EXACTLY that, for EXACTLY this reason. (edit: I may be getting the soources or airlines mixed, but it was reported in this thread already, just not going to search for it).

I would have to have more context before commenting, and hey, I could be wrong, yes. But I'd be surprised if this is a normal occurrence by crews on passenger flights day after day condoned by the airline. My AA 737 NG/MAX friend didn't indicate he was doing much different, but that is an anecdote and I didn't really ask too many details

Look it up, it was very interesting.

I don't want to appear that I am targeting you, I merely jumped into the discussion around where your post was. I take issue with 1: how certain you sounded in your post, considering how unlikely your scenario sounded based off my, admittedly, light 737 NG piloting (just short of 1000 hours) and 2: the whole notion that we currently need an explanation. Wording like "if you have a better explanation" kinda proves my point... whether or not I have an explanation, a better one, lack of one, educated or non-educated guess, etc is irrelevant to whether yours makes sense. It's perfectly valid of me to sit back without a formed opinion and poke holes in the opinion's of others. If I make a claim, then I'll be required to back it up

Fair enough re not targetting me. Appreciate your insight even if I disagree with some of your assumptions. My comment on 'if you have a better explanation' was genuine. That is why I bolded the PLEASE. I am all for alternate theories, but there are a lot of bits and pieces of the data we have so far that does not fit any of the popular narratives.

Also I am not (nor is anyone here AFAIK) part of the investigation, so we don't need to quite as judicious with what we say. Lord knows there are probably 35 pages of it being MCAS, when that doesn't begin to describe the first 3 minutes of the flight, which is arguably where the AC got into trouble.

planecane wrote:

smartplane wrote:

Previous posters compared MCAS to driver assist features on vehicles. In some cases, even when switched off, or even when fuses are pulled, some of these assist features remain in operation.

Suspect MCAS will be similar. In certain flight conditions, in certain settings, different whether being flown from the left or right seat, whether autopilot on or off, or flaps extended or not, MCAS will intervene. Also, MCAS intervention will turn out not to be as linear or predictable as previously thought.

If you disable electric trim MCAS can't operate. MCAS will be predictable. As currently implemented, when it gets bad sensor data it pitches the nose down. If the software engineers at Boeing can't write code to only enable MCAS under certain conditions, how in Earth did they manage to write the code for the 787?

There is no issue with the mcas concept, the issue is that there are no limits or safeguards.

So you are predicting the fix will be software only? I'm sure you are correct following the first accident, based on the Boeing self-initiated enhancement. But not following the second accident. Resolution escalated to hardware and software changes.

smartplane wrote:

planecane wrote:

smartplane wrote:

Previous posters compared MCAS to driver assist features on vehicles. In some cases, even when switched off, or even when fuses are pulled, some of these assist features remain in operation.

Suspect MCAS will be similar. In certain flight conditions, in certain settings, different whether being flown from the left or right seat, whether autopilot on or off, or flaps extended or not, MCAS will intervene. Also, MCAS intervention will turn out not to be as linear or predictable as previously thought.

If you disable electric trim MCAS can't operate. MCAS will be predictable. As currently implemented, when it gets bad sensor data it pitches the nose down. If the software engineers at Boeing can't write code to only enable MCAS under certain conditions, how in Earth did they manage to write the code for the 787?

There is no issue with the mcas concept, the issue is that there are no limits or safeguards.

So you are predicting the fix will be software only? I'm sure you are correct following the first accident, based on the Boeing self-initiated enhancement. But not following the second accident. Resolution escalated to hardware and software changes.

What if MCAS wasn't involved... as we have no evidence it was yet...

mm320cap wrote:

Well, we still don’t know if the Ethiopian accident was even an MCAS event.

Recovered jackscrew shows stabilizer leading edge up, hence nose down (we know that MCAS response to a stall is to put the nose down)
Vertical speed variation from FR24 is similar to Lion Air - the time between peaks is 20 sec. (we know from the Lion Air crash FDR data that MCAS response to a continued stall detection is to cycle the nose-down commands every 15 seconds indefinitely - 10 sec nose down, 5 sec rest, repeat again)
We know the primary cause of Lion Air crash is a badly designed MCAS system.
We know that because Boeing hadn't yet delivered a software patch for that system, the same system exists in the Ethiopian crash.
Common sense: both crashes involve same aircraft model, same high speed dive to earth, during climb out, same call to ATC to return back, both had erroneous airspeed and/or AOA indications

osiris30 wrote:

DeltaMD90 wrote:

osiris30 wrote:

Who the hell said anything about disabling auto-pilot? Just auto-trim... Not sure where you are getting this from, did I misword something in my post that has lead you to suggest they turned off the entire AP system? I am merely suggesting someone hit stab cut-off.

How do you think AP works? There is no "disable MCAS" switch. The stab cutout will disable MCAS but it also disables your electric trim (talking about the electric trim operated by the pilots with their thumb on the yoke) and AP itself.

You would be taking off and flying the entire flight without AP and without electric trim, only the manual wheel

As I understand it, stab cut does not disable all AP functionality. I may be wrong, but I am pretty sure the rest (speed hold, nav hold, AT, etc) all still function if you hit the stab cut switched located beneath .. well beside and beneath the trim wheel. Happy to be corrected, but my understanding is it is not all or nothing.

osiris30 wrote:

Before you say 'wow that would be so weird I have never heard of it', there was a report in the Nasa database of an AA flight crew doing EXACTLY that, for EXACTLY this reason. (edit: I may be getting the soources or airlines mixed, but it was reported in this thread already, just not going to search for it).

I would have to have more context before commenting, and hey, I could be wrong, yes. But I'd be surprised if this is a normal occurrence by crews on passenger flights day after day condoned by the airline. My AA 737 NG/MAX friend didn't indicate he was doing much different, but that is an anecdote and I didn't really ask too many details

Look it up, it was very interesting.

I don't want to appear that I am targeting you, I merely jumped into the discussion around where your post was. I take issue with 1: how certain you sounded in your post, considering how unlikely your scenario sounded based off my, admittedly, light 737 NG piloting (just short of 1000 hours) and 2: the whole notion that we currently need an explanation. Wording like "if you have a better explanation" kinda proves my point... whether or not I have an explanation, a better one, lack of one, educated or non-educated guess, etc is irrelevant to whether yours makes sense. It's perfectly valid of me to sit back without a formed opinion and poke holes in the opinion's of others. If I make a claim, then I'll be required to back it up

Fair enough re not targetting me. Appreciate your insight even if I disagree with some of your assumptions. My comment on 'if you have a better explanation' was genuine. That is why I bolded the PLEASE. I am all for alternate theories, but there are a lot of bits and pieces of the data we have so far that does not fit any of the popular narratives.

Also I am not (nor is anyone here AFAIK) part of the investigation, so we don't need to quite as judicious with what we say. Lord knows there are probably 35 pages of it being MCAS, when that doesn't begin to describe the first 3 minutes of the flight, which is arguably where the AC got into trouble.

For what it's worth to both of you:

I'm purely an outsider with zero plane knowledge looking in. And I find your debate very interesting. Of course it's all speculation. . It's great to hear a pilot point of view Delta. Osiris clearly you know an awful lot about how these planes work. Do you work in the airline industry as well or is it just your interest etc?

Bobbvis wrote:

Having a hard time wrapping my head around trained pilots not being able to overcome a trim system malfunction to the point that it crashes the plane. The thumb switch is right there. If it keeps working against your wishes, reach down and turn it off. The Lion plane flew relatively straight and level for several minutes doing just that and then ???????? Why did they stop correcting it? This flight, I'm not sure we know enough, other than the jackscrew report, but maybe not enough altitude to counter the trim in time? Question- what kind of dive angle does full down trim produce? It's just trim isn't it? Fine adjustment? We're not talking dive bomber here are we?

We don’t have a reason for Ethiopian. But lion air has had a lot of bad situations. It’s a bad airline. Ethiopian also crashed an NG during this decade.

sgrow787 wrote:

mm320cap wrote:

Well, we still don’t know if the Ethiopian accident was even an MCAS event.

Recovered jackscrew shows stabilizer leading edge up, hence nose down (we know that MCAS response to a stall is to put the nose down)
Vertical speed variation from FR24 is similar to Lion Air - the time between peaks is 20 sec. (we know from the Lion Air crash FDR data that MCAS response to a continued stall detection is to cycle the nose-down commands every 15 seconds indefinitely - 10 sec nose down, 5 sec rest, repeat again)
We know the primary cause of Lion Air crash is a badly designed MCAS system.
We know that because Boeing hadn't yet delivered a software patch for that system, the same system exists in the Ethiopian crash.
Common sense: both crashes involve same aircraft model, same high speed dive to earth, during climb out, same call to ATC to return back, both had erroneous airspeed and/or AOA indications

Good theorization and possibly correct but still not conclusive because the investigation is not complete. We're getting ahead of ourselves if we make all too confident prognostications based on as yet incomplete facts. As long as the final jury is still out, we should refrain from making such judgements as definitively linking the two incidents. The Ethiopian crash may yet prove to have a different root cause even if the circumstances appear to be superficially similar at this stage. No criticism, just a word of caution until all of the crash data has been recovered and disseminated.

dtw2hyd wrote:

...Boeing Defense Systems has vast experience with software to control airframes lacking static stability. Most modern fighter planes are inherently unstable for various reasons. So it is not impossible with just software fix for Boeing. Just tighten the loose ends and make it more intuitive to human pilots...

They have but if the electronic stability control fails in a fighter jet, the pilot uses the ejection seat. Not an option for a pax filled airliner. It must be flyable by a crew without exceptional knowledge and skill even when these software gadgets don't work or are switched off.

There are not only Sullys on the flight deck.

dragon6172 wrote:

Or you could use that handy electric trim switch that's right under your thumb on the control column you're pulling so hard on to return the aircraft to a normal trim state before you disable electric trim. As has been pointed out numerous times the pilot ALWAYS has authority over MCAS inputs using the control column electric trim switch.

Do we know that for fact? Could the Max have some logic (for instance, when stickshaker is active), where MCAS overrules control column electric trim switch?

If so, then it's vital to flick Stab Cut Switch immediately. Now the crew have to revert back to manual trim wheel. What's the normal rate your average pilot can obtain using the wheel?
From previous posts in this thread:
* MCAS rate: 0.27 deg/sec
* Control Column Electric Trim Switch: 1 deg/sec
* Manual Trim Wheel: ?? deg/sec.

Can a pilot spin the wheel fast enough to raise the nose, and at the same time maintain enough pulling force on the control column? Probably that would require one pilot pulling hard, and the other one spinning the wheel. Requires very good CRM - and quick, as time is definitely on their side.

osiris30 wrote:

I would have to have more context before commenting, and hey, I could be wrong, yes. But I'd be surprised if this is a normal occurrence by crews on passenger flights day after day condoned by the airline. My AA 737 NG/MAX friend didn't indicate he was doing much different, but that is an anecdote and I didn't really ask too many details

I'd guess that during normal operation, NG/MAX differences will be marginal. Question is how that shows up in non-normal conditions. Would MCAS operation be one of those conditions, where the differences between NG and MAX really show up? If so, to what extent is that covered in the NG --> MAX conversion syllabus?
My understanding is that most MAX pilots were never trained in a "real" MAX simulator.

trpmb6 wrote:

ytz wrote:

Pluto707 wrote:

After 47 pages of posts, my conclusion: MCAS was not the cause, but it gave the final blow

I'm with this too. They had issue right from the take off roll from the looks of it.

What is still sticking with me is that ET's CEO has stated (authoritatively) that the pilots were trained on MCAS and how to handle it.

yes, but go to reality, how many seconds did they have to think about and react to cut out MCAS at this agl ??

DeltaMD90 wrote:

osiris30 wrote:

Who said anything about disabling auto-pilot? Just auto-trim... Not sure where you are getting this from, did I misword something in my post that has lead you to suggest they turned off the entire AP system? I am merely suggesting someone hit stab cut-off.

How do you think AP works? There is no "disable MCAS" switch. The stab cutout will disable MCAS but it also disables your electric trim (talking about the electric trim operated by the pilots with their thumb on the yoke) and AP itself.

You would be taking off and flying the entire flight without AP and without electric trim, only the manual wheel

Per this link, slide 47, the 737NG has two guarded Stab Trim Cut Out Switches:
* MAIN ELECT --> Total isolation of electric trim motor
* AUTO PILOT --> Isolates only auto function trimming, but will still allow Control Column Switch Trimming



It his the same set-up for the MAX?
If so, will Auto Pilot Trim Cut Off isolate MCAS trimming? Or is MCAS trimming considered so important (to prevent approaching stall in certain flight regimes) that MCAS trimming remains active, even when Auto Pilot Stab Trim Cut Out is selected? Which could induce some confusion in an already high workload environment, when crew is faced with *intermittent* auto trimming behavior.

EDIT: answering my own question: MCAS is active only when autopilot is off, which could suggest that MCAS trimming should remain active if AUTO PILOT Trim Cut Off Switch was flicked . . .

PW100 wrote:

dragon6172 wrote:

As has been pointed out numerous times the pilot ALWAYS has authority over MCAS inputs using the control column electric trim switch.

Do we know that for fact? Could the Max have some logic (for instance, when stickshaker is active), where MCAS overrules control column electric trim switch?

Yes its fact. It's also the procedure that's described in the emergency AD that ET CEO says his pilots were trained on. From AD:

Initially, higher control forces may be needed to overcome any stabilizer nose down trim already applied. Electric stabilizer trim can be used to neutralize control column pitch forces before moving the STAB TRIM CUTOUT switches to CUTOUT. Manual stabilizer trim can be used before and after the STAB TRIM CUTOUT switches are moved to CUTOUT.

32andBelow wrote:

We don’t have a reason for Ethiopian. But lion air has had a lot of bad situations. It’s a bad airline. Ethiopian also crashed an NG during this decade.

A crash 10 years ago is relevant here? Both cases involvs brand new planes, not 20y old frames. Brand new planes shouldn’t hit the ground for a software issue, no matter which airline operates them.

PW100 wrote:

DeltaMD90 wrote:

osiris30 wrote:

Who said anything about disabling auto-pilot? Just auto-trim... Not sure where you are getting this from, did I misword something in my post that has lead you to suggest they turned off the entire AP system? I am merely suggesting someone hit stab cut-off.

How do you think AP works? There is no "disable MCAS" switch. The stab cutout will disable MCAS but it also disables your electric trim (talking about the electric trim operated by the pilots with their thumb on the yoke) and AP itself.

You would be taking off and flying the entire flight without AP and without electric trim, only the manual wheel

Per this link, slide 47, the 737NG has two guarded Stab Trim Cut Out Switches:
* MAIN ELECT --> Total isolation of electric trim motor
* AUTO PILOT --> Isolates only auto function trimming, but will still allow Control Column Switch Trimming



It his the same set-up for the MAX?
If so, will Auto Pilot Trim Cut Off isolate MCAS trimming? Or is MCAS trimming considered so important (to prevent approaching stall in certain flight regimes) that MCAS trimming remains active, even when Auto Pilot Stab Trim Cut Out is selected? Which could induce some confusion in an already high workload environment, when crew is faced with *intermittent* auto trimming behavior.

EDIT: answering my own question: MCAS is active only when autopilot is off, which could suggest that MCAS trimming should remain active if AUTO PILOT Trim Cut Off Switch was flicked . . .

Switches renamed primary and backup on MAX. Function the same though. It should be noted that even though MCAS only operates when autopilot is off, the signal does come from the autopilot flight control computer.

AvFanNJ wrote:

sgrow787 wrote:

mm320cap wrote:

Well, we still don’t know if the Ethiopian accident was even an MCAS event.

Recovered jackscrew shows stabilizer leading edge up, hence nose down (we know that MCAS response to a stall is to put the nose down)
Vertical speed variation from FR24 is similar to Lion Air - the time between peaks is 20 sec. (we know from the Lion Air crash FDR data that MCAS response to a continued stall detection is to cycle the nose-down commands every 15 seconds indefinitely - 10 sec nose down, 5 sec rest, repeat again)
We know the primary cause of Lion Air crash is a badly designed MCAS system.
We know that because Boeing hadn't yet delivered a software patch for that system, the same system exists in the Ethiopian crash.
Common sense: both crashes involve same aircraft model, same high speed dive to earth, during climb out, same call to ATC to return back, both had erroneous airspeed and/or AOA indications

Good theorization and possibly correct but still not conclusive because the investigation is not complete. We're getting ahead of ourselves if we make all too confident prognostications based on as yet incomplete facts. As long as the final jury is still out, we should refrain from making such judgements as definitively linking the two incidents. The Ethiopian crash may yet prove to have a different root cause even if the circumstances appear to be superficially similar at this stage. No criticism, just a word of caution until all of the crash data has been recovered and disseminated.

Oops, it looks like the admins have been nice enough to delete my post but forgetting to send me a pm to tell me why. Oh well. It makes sense though. BTW, that's not a "theorization". It's a collection of facts, with the only theory that, if you apply common sense, you will come to the conclusion the Ethiopian crash shares the same root causes as the Lion Air crash, namely a badly designed MCAS.

airkas1 wrote:

Work on the FDR has started.
https://twitter.com/bea_aero/status/110 ... 87361?s=21

Nice image from that tweet. I don't know why, but for some reasons I was expecting something more clean-room like looking



Also, a video clip talking about the process. It's in French, but the guy demonstrates so you can still mostly follow if you don't understand French.

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