I hope I can ask this here. I couldn't find a forum more likely to post this. 

My question to you all is aimed at pilots and PMDG users. The Real World 737 Max accidents were caused by the vertical stabilizer incorrectly forcing the nose into a descent attitude. My question is, couldn't the crew have eliminated that by completely disconnecting the AP and hand flying the aircraft? 

Thanks.

I don't fly in the Sim any of the tube liner's but I do follow aviation news . This is a excellent article on the subject : https://www.seattletimes.com/business/boeing-aerospace/what-led-to-boeings-737-max-crisis-a-qa/

The short answer is no. MCAS is a system that automatically activates even with the autopilot is off when certain conditions are met. The system aggressively attempts to "correct" the planes pitch when it detects a certain angle from the AOA sensor and a few other variables (speed, etc.). If the AOA sensor is faulty, MCAS will kick in with enough force to override manual input repeatedly - again and again and again. 

Disabling the autopilot would have no effect - in fact the system existed to correct conditions that would be far more likely to occur when the aircraft is hand flown vs. being on autopilot, because the autopilot would (presumably) avoid the excessive pitch condition in the first place.

There was a procedure to deactivate MCAS - but you'd first need to realize the MCAS was in fact the root of the problem (and not a mechanical or structural failure, for example), and then you'd need to know what the procedure was. Due to a lack of training (in part because Boeing insisted no training was needed), the pilots of the first crash had neither. During the second fatal crash, the crew did attempt one of the correct remediation procedures - manually trimming the aircraft, but by then the aircraft was going so fast that the manual trim required too much force to actuate.  

You mean the horizontal stabiliser, not the vertical one. But to answer the question, it was not the autopilot which was the problem, it was the MCAS (maneuvering characteristics augmentation system), which is a system designed to automatically input nose-down trim to counter the tendency for the low-slung engines on the 737 to push the nose upwards. This system was not as robustly implemented as it should have been (the redesign of MCAS was what was going on whilst the MAX was grounded, with the system being recalibrated so that it will cut out and no longer put the aeroplane into extreme attitudes if this is looking likely). And so whilst MCAS in its original implementation was something a pilot who was aware of what it did could diagnose it being the cause of the problem and disable the auto-trim, pilots new to the MAX had not been made aware of MCAS on their conversion courses. 

Several pilots did experience extreme trim inputs on the MAX prior to the fatal accidents which grounded the type, and they were fortunate enough to figure out what was the problem, disable the trim and regain control of their aeroplanes, but sadly several pilots did not figure out the problem quickly enough and thus crashed. It's always easy to blame the pilots in such circumstances and say 'they could have done this', but the fact is their 737s were behaving in a manner which they were puzzled by, and in such a situation, if you don't act quickly, it is often too late. In the case of Etheopian Airlines Flight 302, the crew did in fact realise it was an issue with the trim and they disabled it, however, this meant that they could only control the aeroplane by either hauling back really hard on the yokes or by manually cranking the trim wheels, since MCAS had already applied full nose-down trim. So of course is difficult to crank a trim wheel if you daren't let go of the yoke, and especially when the stick forces are high that it takes two of you, so unfortunately, the crew re-engaged the electric yoke-mounted trim buttons in the hopes of using those to cancel out the massive amounts of trim, but unfortunately, doing this also re-enabled the MCAS system and it then applied full nose-down trim again.

Sat in the comfort of a chair, it is easy to say 'they should have done this', but it's different when you are under pressure and your plane is behaving in a strange manner. Making a calm and correct decision in such circumstances is not quite so easy and its just fortunate that some crews managed to recover their MAX 737s or we'd have been looking at a lot more than two crashes. 

The fact is, the B737 MAX pushes an old airframe to the point where it requires far too many compromises to get it to do what Boeing wanted (that is, compete with the A320 NEO without requiring a type re-certification). And you can see this when you work on the thing, it's obvious it is 'past its sell-by date'.

I will give you an example of a problem the compromises of putting large-diameter high-bypass turbofans causes in practical terms: The original B737 was designed to be used with minimal ground equipment, one feature being that it was low to the ground; this is great for opening the cargo holds; you can in fact do this with no steps, which means it is possible to load things into it when you are just stood on the ground, this is not possible on the A320, which you can in fact walk underneath without even ducking down.

The low stance of the original 737 was possible because it used low-bypass turbojets of a narrow diameter, but when Boeing wanted to add high bypass engines to it, they had to flatten the bottom of the cowlings just to fit them on it. This means it is far more prone to FOD damage, but it also means the thrust line of the engines is low down which is what necessitates that MCAS system, since this was made worse by adding even larger diameter engines to the MAX, so they had to extend the landing gear legs a bit to give it more ground clearance, but what this now means is that you can barely reach the ground power socket to plug it in, and when headsetting the thing out, if you are not tall, it is impossible to remove the headset and close the panel. This means half the people who work on the ramp cannot headset out a 737 MAX because they are simply not tall enough to be able to do so; I can just about reach it, but even I have to pull the wire of the headset, rather than pulling on the jack itself in order to get the thing out, and I can only just reach the top-most press-stud to secure the access door.

This is why all that stuff on the A320 is on the underside of the fuselage, which means that even though the A320 sits much higher off the ground than the 737, everyone can reach that access panel.

This is not the first time Boeing compromised with the 737's design either: If you look at the original B737, you will see it has no dorsal fillet, but when Boeing wanted to start putting high-bypass CFMs on the newer version, they had originally intended to make the tailfin taller in order to improve its stability. However, lots of airlines who had bought the original 737 had built their hangars to fit their original 737s, meaning a new one with a taller fin would not fit in their hangars, so they started looking at buying the BAC 1-11 and DC-9 instead. Not wishing to lose customers, Boeing compromised and added that dorsal fillet instead of making the fin taller. It worked, but it is an example of the cart leading the horse, which is never a good idea with aeroplane design and it has been a feature of all the new 737s that compromises have been made in order to maintain the same type certificate so that customers would buy new versions and not have to spend a lot on certifying their pilots with a completely new type rating.

The MAX is now safe to fly on, although it says a lot that they don't even call it the MAX now, it's the 737-8, so I wouldn't want to put people off getting on one, but really, Boeing should have canned the type after the NG variant and started with a clean sheet design rather than trying to turn a sixty year old airframe into something it can never really be, instead making something which could eclipse the A320 on its own terms and attract customers who would buy a new type because it was good, rather than a tarted-up old banger just because they could save a few quid on type ratings and it would fit in their hangar.

 

Edited October 27, 20214 yr by Chock

I might add: The bottom line is they cut corners because they did not want to have to retrain all Max pilots regarding the MCAS system (additional cost to the airlines/Boeing) and a lot of things where done hush hush and the software was NOT the way it should have been regarding redundancies. 

Mark Forkner, then chief test pilot of Boeing, has been indicted for fraud in the two Max crashes. 

It is really a sad story of cost cutting over safety....

On the west coast of the US at 10:00 pm on frontline (PBS) they are telling the story behind the Max, should be good.

5 hours ago, MartinRex007 said:

On the west coast of the US at 10:00 pm on frontline (PBS) they are telling the story behind the Max, should be good.

 

 

I'd rather recommend more technical explanation form Chris Brady

1 hour ago, C2615 said:

I'd rather recommend more technical explanation form Chris Brady

Yup, agree. He's been my go to source for 737 stuff for years and I strongly recommend his book if anyone really wants to know about the 737 in great detail.

I believe, and I'm hardly alone, that the Boeing Corporation rushed-out the 737 Max to compete the the new, more efficient Airbus that was about to be released: The need to compete.  Re-training 737 Max pilots around the world most likely would have delayed sales... 

But, as we now know, the new MCAS system was flawed and some unsuspecting pilots were handed the keys to fly it...   

1 hour ago, overspeed3 said:

Re-training 737 Max pilots around the world most likely would have delayed sales... 

It's not so much that it would have delayed sales, more that it might potentially have prevented sales altogether. If, as could be argued, the new 737 variant was in spite of its similar numerical designation, deemed to be different enough to require new type certification training, then that is an additional expense for existing NG customers who were considering the MAX as opposed to the A320 largely because of its transitional ease with regard to operation. This is why it has long been Boeing's desire to keep successive 737 models on the same general type-rating so as to make new models an attractive proposition to customers which had preceding models in their fleet, since all they'd have to do, is have their pilots do a simple self-study update to be deemed competent on the new type.

The changes to new versions of 737s, where overly-simple variant conversion training courses for crews were again the norm, has in the past led to fatal accidents. For example, it was a definite factor in the Kegworth crash of BMI 737-400 flight 092 where again an experienced 737 crew (on a previous variant) assumed incorrect things based on their knowledge of previous variants combined with a lack of familiarity with the engine instrumentation on the 400. Although in fairness to Boeing, some blame for that BMI crash has to be laid at the door of BMI's engineers too, who instead of directing the crew of the aeroplane to land immediately at somewhere suitable, instead had them fly past numerous airports including Liverpool and Manchester where they might have landed safely, simply because they wanted to get the aeroplane to one of their convenient service airports.

So again that was a case of trying to save money at the expense of passenger's lives, which was an all-too familiar tune in the past, and regrettably, the MCAS fiasco is is an unwelcome reprise of that tune. If the new 737 variant had required a different type rating, the airlines which might potentially replace their NGs with the MAX, might just as well have opted for replacing their NGs with  A320s, which is what Boeing were trying to avoid, but doing so 'on the cheap' and with their fingers crossed to a very large extent. This is one of the chief motivations for why Boeing were less than forthcoming about the differences and training requirements for the new MAX, and as it turns out, that's ended up costing them more in cash and reputation than it would have done if they'd have just gone with a new aeroplane design in the first place, which they are now having to do anyway, not least because the MAX is already a bridge too far in terms of development potential; there's just no way they can push that airframe design any further. It's a very sad state of affairs for what used to be the best aeroplane company in the world.

Edited October 27, 20214 yr by Chock

So, would turning off Stab Trim on the pedestal turn off MCAS? It would be interesting if PMDG coded MCAS failure into their simulation.