Netflix Releases Documentary on the Boeing MCAS Failures

[hindsight2020]

That’s because most pilots not trained in the west are procedural only. They can’t actually fly for ****. Pretty much every single pilot on this board is a better stick and rudder pilot with a more natural understanding of airmanship than the ones flying that day. Even @steingar is better.

*cough* Colgan *cough* 3407 *cough*

 

[ARFlyer]

*cough* Colgan *cough* 3407 *cough*

Yes the CA had multiple 121 checkride failures.

However, the accident was mostly fatigue induced. Both had commuted from across the country with the FO having came from the West Coast via a red eye cargo flight and slept in the crew room. NTSB and the FAA got really really close to outlawing commuting. ALPA and APA freaked out and got them to back off about the time the families started lobbying Congress to fix the “training issue”. So that was muffled out by the R-ATP bandaid that Congress did to appease the families.


On the MAX issue, Boeing needs to clean sheet their next narrow body. The 737 is a early 60s design that is tapped out. MCAS is proof of that issue.

You can’t add efficient engines without either raising the gear height or pushing the engines forward and up. The latter was chosen and MCAS was needed to fix a stability issue at high AOAs. Then Boeing found themselves in a bind with the airlines, especially Southwest. Admit to MCAS and require Type C Differences or a new Type Rating. The airlines would balk at having to do sim training to satisfy C Differences or the huge cost of adding a new type rating. So Boeing hid MCAS so it would be a Type A differences which came to be just a iPad Course. Their ODAs didn’t know the truth much less enough to pass on information to the FAA for the FAA Engineers to know what they’re looking at.

Boeing isn’t the first. Bombardier did it with the CRJ. The CRJ-200 is vastly different then the CRJ-700/900. Yet they’re all under the CL-65 type rating. When the 700/900 was designed it originally had the modern 220 cockpit and systems. But the regional airlines screamed bloody murder because the FAA was going to require a new type rating due to the differences. So Bombardier relented and slapped the CRJ-200 cockpit back in with some of the systems slightly automated. So now you have a 2020 Year Model 900 being built with cathode ray tube screens from the 90s. You also have pilots slamming 900s into the runway, almost stalling out 200s, and blowing up 200 engines at start because they can fly all three variants under the same rating...

 

[Tarheelpilot]

Yes the CA had multiple 121 checkride failures.

However, the accident was mostly fatigue induced. Both had commuted from across the country with the FO having came from the West Coast via a red eye cargo flight and slept in the crew room. NTSB and the FAA got really really close to outlawing commuting. ALPA and APA freaked out and got them to back off about the time the families started lobbying Congress to fix the “training issue”. So that was muffled out by the R-ATP bandaid that Congress did to appease the families.


On the MAX issue, Boeing needs to clean sheet their next narrow body. The 737 is a early 60s design that is tapped out. MCAS is proof of that issue.

You can’t add efficient engines without either raising the gear height or pushing the engines forward and up. The latter was chosen and MCAS was needed to fix a stability issue at high AOAs. Then Boeing found themselves in a bind with the airlines, especially Southwest. Admit to MCAS and require Type C Differences or a new Type Rating. The airlines would balk at having to do sim training to satisfy C Differences or the huge cost of adding a new type rating. So Boeing hid MCAS so it would be a Type A differences which came to be just a iPad Course. Their ODAs didn’t know the truth much less enough to pass on information to the FAA for the FAA Engineers to know what they’re looking at.

Boeing isn’t the first. Bombardier did it with the CRJ. The CRJ-200 is vastly different then the CRJ-700/900. Yet they’re all under the CL-65 type rating. When the 700/900 was designed it originally had the modern 220 cockpit and systems. But the regional airlines screamed bloody murder because the FAA was going to require a new type rating due to the differences. So Bombardier relented and slapped the CRJ-200 cockpit back in with some of the systems slightly automated. So now you have a 2020 Year Model 900 being built with cathode ray tube screens from the 90s. You also have pilots slamming 900s into the runway, almost stalling out 200s, and blowing up 200 engines at start because they can fly all three variants under the same rating...

This…
Having flown the hat trick of all three cl-65 types in one day as a reserve captain I can verify it is not to be taken lightly. I still have no idea how the airline convinced the FAA that was a good idea.

 

[Sluggo63]

I really don’t have the desire or energy to rehash the whole thing again.

If the nose is heavy, trim it back up. That's what we do when we're hand flying. If the trim gets to full nose-down, nobody was flying the airplane.

1. Fly the airplane
2. Silence the warnings
3. Confirm the emergency

That's all well and good on 0 knots and 1 G, but that's easier said than done, isn't it.

C'mon. We both know how sim training goes. Yes, we're all well trained, but we also know "the drill" we go through every 12-18 months. To think that the "runaway stab trim" they experienced in both those crashes resembles anything they, you or I was trained on in any sim we've been to, I've got news for you... it didn't. Because of this:

Yea let's not forget you have stall warning, unreliable airspeed and altitude, master warning with multiple messages on your displays, no idea that MCAS even exists and about a minute and a half to figure it all out. Even if they didn't do everything perfect to the T like a mythical Steve Canyon nobody here has any business bad mouthing them.

The whole "no multiple emergencies" edict that the FAA has is why. When we practice "runaway trim" we know it's coming (thanks, AQP) and it's done as a stand-alone problem. These guys had dozens of EICAS messages so sort through, cautions, warnings, confusion. All while trying to fight a plane that was fighting back, and find a checklist that didn't exist in a QRH for a problem with a system that they didn't even know was on the airplane. In addition to that, it doesn't even present as "old school runaway trim," (i.e. the trim wheel doesn't spin continuously, the trim brake doesn't stop the trim).

I may certainly be in that category, and I definitely respect your knowledge and experience in this area. I thought I read that use of the electric trim to pitch up would arrest, at least temporarily, the MCAS automatic nose down pitch input. Is that not true?

It is true. They could (and at certain points did) stop the trim wheel. But I can see a scenario that played out something like this: the captain is flying and MCAS is continually trimming the aircraft nose down. The center MFD is filled with EICAS messages and the warning bell is ringing. The FO is trying to open the QRH and diagnose the problem, but he can't find anything that looks like it fits the problem they have. The captain looks down to help him, gets distracted and the MCAS cycles and now the plane is out of trim. Now it's harder and harder to get back into trim. The whole things spirals from there...

That’s because most pilots not trained in the west are procedural only. They can’t actually fly for ****. Pretty much every single pilot on this board is a better stick and rudder pilot with a more natural understanding of airmanship than the ones flying that day. Even @steingar is better.

I'd be careful painting with such a wide brush because...

*cough* Colgan *cough* 3407 *cough*

...and Atlas 3591
...and American 587
...and American 965
...and FedEx 1478
...and Delta 1141
...and the list goes on.

It's funny how the early days after the crashes (love him or hate him), Sully was beating the "foreign pilots bad" drum (https://tinyurl.com/mdrm9fzk).

But after going into the sim and replicating the MAX scenario, he quickly changes his tune (https://tinyurl.com/ytar8yvj).

It's second hand information, but after talking to someone who was involved in the scenario recreation, it didn't go real well for the US pilots sitting in that sim. And that was with the foresight of knowing what was going to happen.

I'm not ready to say that I or anyone else wouldn't have had the same outcome. Maybe I would have, maybe I wouldn't have, but then again I've never been in that scenario in an airplane where I'm literally fighting for my life.

 

[Sluggo63]

This…
Having flown the hat trick of all three cl-65 types in one day as a reserve captain I can verify it is not to be taken lightly. I still have no idea how the airline convinced the FAA that was a good idea.

Right... or MD-10/MD-11 on the same type.

 

[35 AoA]

Not a 121 dude, but there was a period of my life when I held three different NATOPS quals at the same time; Legacy Hornet, Super Hornet, and Viper/Fighting Falcon. Hornet and SH are outwardly similar, but the systems and basic procedures between an A/B model (which we had a handful of) and an E/F are different in significant ways (C/D and E/F comparison is more nuanced at a systems and procedures level, though there are still major differences). Viper was like 180 out......everything on the left in one, was on the right in the others (well maybe not the throttle). Long way of saying it was a lot to keep track of, if I was really being honest about my proficiency in each. Only way it worked was I did it every day. There were a few 24 hour periods in that tour where I flew all 3. And sometimes "same same but different" is harder than just "different".

 

[Tarheelpilot]

That's all well and good on 0 knots and 1 G, but that's easier said than done, isn't it.

C'mon. We both know how sim training goes. Yes, we're all well trained, but we also know "the drill" we go through every 12-18 months. To think that the "runaway stab trim" they experienced in both those crashes resembles anything they, you or I was trained on in any sim we've been to, I've got news for you... it didn't. Because of this:



The whole "no multiple emergencies" edict that the FAA has is why. When we practice "runaway trim" we know it's coming (thanks, AQP) and it's done as a stand-alone problem. These guys had dozens of EICAS messages so sort through, cautions, warnings, confusion. All while trying to fight a plane that was fighting back, and find a checklist that didn't exist in a QRH for a problem with a system that they didn't even know was on the airplane. In addition to that, it doesn't even present as "old school runaway trim," (i.e. the trim wheel doesn't spin continuously, the trim brake doesn't stop the trim).

It is true. They could (and at certain points did) stop the trim wheel. But I can see a scenario that played out something like this: the captain is flying and MCAS is continually trimming the aircraft nose down. The center MFD is filled with EICAS messages and the warning bell is ringing. The FO is trying to open the QRH and diagnose the problem, but he can't find anything that looks like it fits the problem they have. The captain looks down to help him, gets distracted and the MCAS cycles and now the plane is out of trim. Now it's harder and harder to get back into trim. The whole things spirals from there...



I'd be careful painting with such a wide brush because...



...and Atlas 3591
...and American 587
...and American 965
...and FedEx 1478
...and Delta 1141
...and the list goes on.

It's funny how the early days after the crashes (love him or hate him), Sully was beating the "foreign pilots bad" drum (https://tinyurl.com/mdrm9fzk).

But after going into the sim and replicating the MAX scenario, he quickly changes his tune (https://tinyurl.com/ytar8yvj).

It's second hand information, but after talking to someone who was involved in the scenario recreation, it didn't go real well for the US pilots sitting in that sim. And that was with the foresight of knowing what was going to happen.

I'm not ready to say that I or anyone else wouldn't have had the same outcome. Maybe I would have, maybe I wouldn't have, but then again I've never been in that scenario in an airplane where I'm literally fighting for my life.

I agree but then when you go look at the MCAS events fleet wide and there were only two crashes…

I don’t think anyone here is saying there was nothing wrong with how MCAS was managed because it was clearly mismanaged. But the max is not a **** airplane. There are a few people here connecting dots that don’t line up and subsequently making statements not supported by fact.

Edit: I know I was painting with a broad brush. It was mostly being used as an example of changing the color of paint while borrowing the brush from some other posters in this thread.

 

[FlyingTiger]

Just because there was a significant issue with the product doesn't mean that the crews and the airlines can't have also made mistakes. There is clear evidence of their failures in both of these accidents.

1) When the Lion Air plane was acting up on the flight before, they should have taken the plane out of service and maintenance should have fixed the problem with the AOA sensor. Instead, the pilots simply disabled the auto trim feature, flew to their destination, and let the aircraft be used again without repairs.

2) When MCAS auto-trims nose down, the pilots can use the electric trim switch to re-trim. We all learned from day one to trim the plane to relieve pressure on the controls as private pilots. That isn't hard. It should have been their first instinct. Once back in trim, then you can disable the auto trim feature just like the pilot is supposed to do for any other auto-trim runaway failure and then trim manually. The only thing different in terms of this auto-trim failure mode is that it would run for ten seconds and stop, rather than just run away. But there is no reason why the crew shouldn't have responded as they should have to any other runaway trim failure. That is the expectation for a professional pilot crews entrusted with the lives of over a hundred souls on a transport category aircraft.

The documentary notes that the Ethiopian Air pilots disabled the auto-trim like they were supposed to. However, they failed to mention that the captain had been retrimming the aircraft to counteract the MCAS activation for some time, but when he transferred control to the first office, the first officer failed to do so and let it get all the way to full downward force before they disable the auto-trim. At that point, the aerodynamic forces made it nearly impossible to manually retrim. On top of that, the pilots failed to reduce power as provided in the manual, which had they done so, would have given more time and reduced the aerodynamic forces resisting their effort to re-trim.

Your first comment actually supports my point. Airlines defer maintenance all the time when it is allowed by the MEL. If Lion Air was actually aware that a defective AOA could make the plane want to dive into the ground due to MCAS, I imagine they would have fixed it.

As to your second comment, two things. First, comparing a private pilots experience with trim in a small single engine plane with the trim system of a 737 Max is rather dubious. Secondly, the plane had multiple warnings and anomalies that would not occur in a "simple" runaway trim event. See post 84 by Sluggo for a more detailed explanation.

 

[Mahneuvers]

Total thread jack, but I just sat down to watch the documentary and wound up binge watching Space Force instead.

I watched the Boeing/MCAS documentary b/c of this thread. I don't watch many documentaries, but, my take was 15 minutes of information and the rest filler. I contemplated Space Force but ended up spending the day watching "WWII in Color". Talk about the exact opposite signal to noise ratio! I'm no history buff, but even so, was surprised how much I learned.

 

[PPC1052]

Your first comment actually supports my point. Airlines defer maintenance all the time when it is allowed by the MEL. If Lion Air was actually aware that a defective AOA could make the plane want to dive into the ground due to MCAS, I imagine they would have fixed it.

I am not aware of any rule that would allow them to simply ignore it, even assuming the system is not required under an MEL (which is doubtful for this system), and not disable the system if inop and placard it to just let the next crew find the issue on their own. Are you?

 

[bflynn]

Even with MCAS, the FAA would not allow a US airline to operate three generations of the 737 as a single qualification. SWA had to park their remaining Classics (737-500s, IIRC) before they could operate the MAX. The 737-200 isn't even a Classic. That's the original generation that was followed by the Classics (737-300 through -500).

Sorry for jumping back three screen, but this isn't technically accurate. The FAA would absolutely allow an airline to operate a 300 and MAX at the same time. They did not allow the 300/500 and MAX to be in the same pilot qual. Pilots could have 300/500/700/800 or 700/800/MAX, but that would require tracking and scheduling pilots with different qualifications. SWA wanted to retire the older airplanes anyway, so the decision was made to retire the airplanes early and focus on the MAX.

 

[dmspilot]

If Lion Air was actually aware that a defective AOA could make the plane want to dive into the ground due to MCAS, I imagine they would have fixed it.

Imagination shouldn't enter into it. Highly unlikely an AOA sensor is deferrable per MEL. In the aircraft I fly, the only thing that may be inoperative with regard to AOA sensors is the heating system on one of them, and that's only if the aircraft is not operated into icing conditions.

 

[Bell206]

If Lion Air was actually aware that a defective AOA could make the plane want to dive into the ground due to MCAS, I imagine they would have fixed it.

FYI: the AoA sensor was replaced the day prior to the accident flight due to an unrelated discrepancy. On the subsequent flight after replacement, the MCAS activated with L/H stick shaker and multiple warnings due to an erroneous AoA signal from the replacement unit. While the PIC/SIC flying attempted to remedy the situation a 3rd pilot in the jump seat recommended to the PIC to actuate the stabilizer cut-off switches which stopped the MCAS activations and the flight continued. Unfortunately, after landing the PIC did not write up the stick shaker activation or the use of the trim cut-off switches which did not permit the entire problem to corrected by ground support.

 

[Larry in TN]

These guys had dozens of EICAS messages so sort through

737s don't have EICAS.

But I can see a scenario...

Your scenario is nothing like what happened. Read the (long) article that I linked to above. It takes you, in detail, through both accident flights and the preceding incident flight on the Lion Air accident airplane.

Read that article and come back here and tell me you find the performance of any of those three crews to be acceptable for an airline crew.

I try to avoid using the appeal to authority fallacy, but my comments come from seven years of flying 737s, including the MAX, and going through all of the runaway stabilizer, MCAS activation, and the progression of manual trim techniques, including at barber pole, drills in the simulator.

Here's the link again so you don't have to scroll back to find it. https://seekingalpha.com/instablog/...930-boeing-737-max-8-crashes-case-pilot-error

If Lion Air was actually aware that a defective AOA could make the plane want to dive into the ground due to MCAS, I imagine they would have fixed it.

Lion Air installed an unairworthy (not properly overhauled and tested) AoA vane/sensor on the accident airplane.

The FAA would absolutely allow an airline to operate a 300 and MAX at the same time. They did not allow the 300/500 and MAX to be in the same pilot qual.

That's what I said.

No airline has attempted to operate both the 737-200 and MAX with a common qualification. That was never an issue.

 

[Sluggo63]

737s don't have EICAS.

Thanks. I actually knew that. To me, that's even worse...

I try to avoid using the appeal to authority fallacy, but my comments come from seven years of flying 737s, including the MAX, and going through all of the runaway stabilizer, MCAS activation, and the progression of manual trim techniques, including at barber pole, drills in the simulator.

This is what I'm saying. You and I both know how those sim events go. There's a 2 hour pre-brief, along with pre-sim study material. AQP means that you know what is going to be covered in that sim ride. You're going into the box knowing exactly what's going to be thrown at you. If you think that's an accurate representation of what those crews faced, I'm going to vehemently disagree with you.

Just look at the FOQA data over the last years on how Part 121 Go-Arounds have fared. Spoiler alert: they're not good. And that's a normal go around. Something that every pilot should be proficient at, and is done every sim event. But it seems that US trained pilots manage to muck that up on a regular basis because it's (usually) not planned and something that is only done once every 9 months (or 6 or 12, whatever your airline's training program dictates).

I'm not saying that these pilots performed outstandingly and/or there aren't things that they could have done differently. What I am saying is, 1. these guys faced a problem that they didn't know could happen, in a way that they have never been trained for, and were trying to figure it out on the fly; and 2. that if these events happened to a US pilot flying with a Part 121 airline here in the states, I'd bet dollars to donuts that there is a better than even chance that the outcome would have been the same.

And that seems to be the case if what my 737 LCA friend told me about the post-crash MCAS sim recreations are true.

And I'll let you have the last word on this. I'm not interested in going around and around on this again. We're not going to agree, and that's fine. I just hope no one has to be in the position that those guys found themselves in.

 

[Silvaire]

...Read that article and come back here and tell me you find the performance of any of those three crews to be acceptable for an airline crew...

Okay, I read the article. There are actually two articles written by the same guy, the second one is linked to in the first paragraph and it goes into the MCAS culpability in which the author states:

"..Under these circumstances, we are not sure that any pilot could have saved these aircraft."

 

[bflynn]

Even with MCAS, the FAA would not allow a US airline to operate three generations of the 737 as a single qualification. SWA had to park their remaining Classics (737-500s, IIRC) before they could operate the MAX.

That's what I said.

No airline has attempted to operate both the 737-200 and MAX with a common qualification. That was never an issue.

Sorry, I misread. Southwest wanted to do it, but wasn't allowed.

BTW, SWA retired the 200 long before the MAX was around. They only had 300/500s lefts

 

[PPC1052]

Okay, I read the article. There are actually two articles written by the same guy, the second one is linked to in the first paragraph and it goes into the MCAS culpability in which the author states:

"..Under these circumstances, we are not sure that any pilot could have saved these aircraft."

Those "circumstances" being after the pilots let the nose down trim get so great that "neither manual trim or brute force could overcome the nose down force." Also, the author's assumption is that the autothrottle is still on, rather than retarded. No doubt, there comes a point where it become impossible, or nearly so, to avoid a crash. But the author is not saying it is impossible if the pilots use the electric trim to remove the downward nose trim before it gets to that point.

If the pilots did not fully trim out the MCAS trim position (nose down) then when it reactivates it starts from that spot, which may have been a nose down position. This would compound the problem each time the MCAS activates and a new more severe nose down position develops. At some point, the control column presser is so great that neither the manual trim or brute force could overcome the nose down movement. And unlike STS, where the movement of the control column (yoke) shuts off the automatic trim, the control column does not shutoff for MCAS. Each accident occurred around the five to six-minute point meaning that the difficulty to keep the nose up was so great the pilots eventually lost the battle with the aircraft system, plunging straight down at excessive speeds (remember the auto throttles are probably still at a high-power setting thinking the aircraft is stalled). Under these circumstances, we are not sure that any pilot could have saved these aircraft.
​

In fact, the author states in the very next paragraph:

Regardless of software and/or hardware failures or flight conditions, the outcome would have been very different if the pilots had deactivated the stabilizer trim—an already established emergency action procedure in the 737 MAX series aircraft.​

 

[Larry in TN]

BTW, SWA retired the 200 long before the MAX was around. They only had 300/500s lefts

Unless I mistyped earlier, that's what I said before. They parked the -500 in order to introduce the MAX in the same qualification as their remaining 737s, all NGs. AFAIK, no airline ever attempted to operate the MAX in a common qualification with any original or Classic 737.

In any case, if you fly the airplane first, the unscheduled MCAS activation should not have endangered the flight regardless of how little you knew about MCAS. When the nose gets heavy, you trim the nose up. That's what we do day in and day out hand-flying the airplane. If you can't ignore some warnings going off while you continue to fly the airplane, you shouldn't be flying an airliner. One pilot flies the airplane while the other pilot deals with the warnings.

And it's not just what they didn't do that is so horrendous, read the things that they did do.

 

[mryan75]

It most certainly is true. MCAS is there to simulate a 737-200

MCAS was never designed to engage during any normal flight regime. If MCAS engaged, you were already in trouble.

 

[midwestpa24]

MCAS was never designed to engage during any normal flight regime. If MCAS engaged, you were already in trouble.

The problem isn't what MCAS was designed to do. The problem is the new failure mode MCAS created, one that was not easily recognized by pilots. Any time a system is changed or added in a design this is always a possibility, unintended consequences. That's why aircraft certifications, type certificated, STCs and such are all so difficult. You don't just have to prove something does what it's supposed to, but that it isn't going to have unintended consequences. Think of the Tamarack winglets and the accident caused when one malfunctioned. Or even the uncommanded vehicle acceleration issues from a few years ago that was eventually blamed on aftermarket floor mats blocking the accelerator pedal.

 

[Mxfarm]

MCAS was never designed to engage during any normal flight regime. If MCAS engaged, you were already in trouble.

and didn’t know it<?>

 

[mryan75]

The problem isn't what MCAS was designed to do. The problem is the new failure mode MCAS created, one that was not easily recognized by pilots. Any time a system is changed or added in a design this is always a possibility, unintended consequences. That's why aircraft certifications, type certificated, STCs and such are all so difficult. You don't just have to prove something does what it's supposed to, but that it isn't going to have unintended consequences. Think of the Tamarack winglets and the accident caused when one malfunctioned. Or even the uncommanded vehicle acceleration issues from a few years ago that was eventually blamed on aftermarket floor mats blocking the accelerator pedal.

I get that and you're correct. I'm just pointing out it was not implemented to make the MAX handle like a -200.

 

[FlyingTexasTiger]

Sure would be nice to know which airline management group our posters are employed by!

 

[JimNtexas]

It does mention that the Lion Air pilots didn't flip the switches off. It also says that Lion Air tried to get more training for the system and was ridiculed for it. It mentions that the Ethiopian air Pilots flipped the switches off but the by then the plane was unrecoverable. It mentions that Boeing's analysis showed that if actions were not taken within 10 seconds the plane would be unrecoverable. The documentary is not very sympathetic to the airplane manufacturer. Watching the testimony of the executives brought to mind Hannah Arendt's phrase "the banality of evil".

Ethiopia followed the Checklist and MCAS was disabled. They then got concerned because the trim wheel was hard to move. So they reengaged stab trim and died.

Why was the trim wheel hard to move? BECAUSE THEY LEFT POWER AT TAKEOFF THRUST AND WERE GOING 600 KNOTS.

 

[Mahneuvers]

Started watching METAL of HONOR. OMG, I'm so impressed by these men.

 

[SkyDog58]

The minute I saw that it was co-produced and directed by Rory Kennedy (Robert F. Kennedy's daughter) I knew it was going to be a hit piece..

How so?

 

[Piperonca]

Former Boeing Technical pilot Mark Forkner not guilty, says jury today.
https://www.cbsnews.com/news/boeing-test-pilot-mark-forkner-not-guilty-of-deceiving-faa/

 

[kmacht]

I confused on the charges. Why “wire fraud”? Sees like wire fraud is much different than what he was being accused of by n the article.

 

[Bell206]

Why “wire fraud”?

The "wire" part refers to any type of electronic communication. He was accused of discussing/sending fraudulent MCAS training reports to the FAA via phone calls/emails on which the FAA made their regulatory decisions.

 

[steingar]

When this whole thing started I was incredulous that they would have an important system like MCAS depend on one blade on the nose of the aircraft. All kinds of things could happen to that blade. You can pack enough stuff to tell your exact position on the Earth and velocity into a matchbox, and they're making this enormously important system depend on a single very vulnerable piece of hardware. That's pretty damning in and of itself in the Book of Steingar. No redundancy.

 

[Steamflyer]

My recollection is that MCAS was originally tuned to prevent excessive pitch up in high speed steep turns due to some lift generated by forward placed nacelles due to bigger engines. Later MCAS was also made to engage at low speeds and high angles of attack to meet the stick force vs. AoA gradient. For whatever reason at this point it was also given independent authority to roll trim all the way forward if computer felt was necessary based on AoA. That seems to be the final hole in the Swiss cheese from a design standpoint since a faulty AoA input could lead to erroneous full forward trim being applied by MCAS, which is believed to be the root cause.

Regardless, if the trim wheel is furiously running, it's a runway trim and the autotrim, whatever it happens to be called, must be killed. The 737 MAX has two massive switches to do just that. In addition, if screaming along at low altitude, pull the throttles and trade airspeed for altitude while simultaneously reducing stick forces. Leaving them firewalled seems to indicate mental overload. Because at some point a combination of full forward trim and high airspeed will become unrecoverable.

 

[Sluggo63]

Because at some point a combination of full forward trim and high airspeed will become unrecoverable.

But with full forward trim, don't you need high airspeed to neutralize the stick forces (i.e., if the stab is trimmed forward/nose down, it's trimmed for a higher speed than you currently are). In that case, increasing speed will bring the plane "back into trim" and stick forces would normalize. Now, with the stab full forward you probably can't get fast enough to get it back into trim, but depending where the stab stopped, flying faster may not be the worst thing to do.

 

[Scrabo]

I watched the first 20 mins of it and was not impressed by it, seem to be a lot of filler.

 

[Larry in TN]

But with full forward trim, don't you need high airspeed to neutralize the stick forces

How did it get to full forward trim? It takes quite a while to get there.

If the nose is getting heavy while you're hand-flying, what do you do? The yoke trim thumb switches override MCAS and allow you to trim out any, and all, nose-down trim input it had applied. Five seconds later it would do it again but you can stop it and remove what it did again with just a momentary nose-up trim input with the thumb-switches.

 

[SoCalAviator]

The specific undesirable trait that required MCAS occurs only at aircraft states that should never occur during normal operations.

And yet it did occur.

 

[Larry in TN]

And yet it did occur.

No, it didn't. All three events were unscheduled MCAS activations.

 

[Palmpilot]

No, it didn't. All three events were unscheduled MCAS activations.

By "unscheduled," do you mean that the MCAS activation was brought about by the malfunction of a component or components, rather than operation at an attitude that was supposed to activate it?

 

[Larry in TN]

By "unscheduled," do you mean that the MCAS activation was brought about by the malfunction of a component or components, rather than operation at an attitude that was supposed to activate it?

I mean that the conditions under which MCAS was designed to activate did not exist. i.e. abnormally high AoA.

On the Lion Air incident and accident flights, the unscheduled activation was due to the airline installing an unserviceable AoA sensor on the airplane.

On the Ethiopian flight, the left AoA vane was broken off by a bird strike at liftoff.

As far as I know, a 737 MAX has never had a scheduled MCAS activation on an operational flight. Things would have to go very wrong for them to reach such a high AoA.

 

[AA5Bman]

Okay, just tuning into this thread. I just watched the documentary (while flying cattle class on a 737, it should be stated), and wanted to see if I could make sense of what happened.

It seems obvious, as in many situations, that there is enough blame to go around for everyone. Clearly Boeing cut some corners. Less clear from the documentary is that the pilots made some mistakes. In the documentary it goes into great length to talk about how Boeing concealed the MCAS system and while that was wrong, is it not true that this MCAS failure mode is just a special case of runaway trim? This was my understanding going in to the documentary, and if it is true, it seems to follow that Boeing might have a leg to stand on - regardless of the source of the runaway trim, if runaway trim scenarios are covered elsewhere in training, this is just one of those scenarios.

The part that is news to me is that the Ethiopian pilots *did* actually disable the electronic trim system, but still crashed (?). Is this accurate? In reading through this thread, it seems like they made some other mistakes as well - not reducing throttle, for instance. Was their trim situation, in fact, unrecoverable? If it was unrecoverable, it seems to place the blame squarely on Boeing’s shoulders. If it recoverable, it seems like the pilots share some of that burden.

Were there other events where MCAS went haywire and the pilots *did* disable the auto-trim feature AND recover safely? It sounds like there were and I remember that from reading elsewhere around the time of the accidents.