Ethiopia crash

[scott967 62]

I have a problem understanding some of the logic in the MCAS design.  I get that certification requirements result in the need for augmentation in the pitch axis, and I guess augmentation is allowed.  What I don't see is 

 

1.  Why the MCAS is inhibited when pilot operates the elec trim switches on the column.  I assume the idea was the "pilot knows what he is doing" (but the column cut-out switch does not inhibit MCAS).

 

2.  When the pilot stops operating the elec trim switch, MCAS "waits" for several seconds before starting a new down-trim order.  What's the reason for the delay?  I can't believe it's to allow sensors to "settle down" after a transient.

 

Both of these design/implementation features seem to me to add cognitive workload to pilot in recognizing trim "runaway" (which isn't really running away).  As pilots have pointed out, other systems also operated on trim, such as STS so you have to evaluate unwanted "MCAS" trim in a noisy  (as in, aircraft is moving the stab up or down for other reasons) environment.

 

scott s.

.

 

 

 

[John_Cillis 2,406]

55 minutes ago, scott967 said:

I have a problem understanding some of the logic in the MCAS design.  I get that certification requirements result in the need for augmentation in the pitch axis, and I guess augmentation is allowed.  What I don't see is 

 

1.  Why the MCAS is inhibited when pilot operates the elec trim switches on the column.  I assume the idea was the "pilot knows what he is doing" (but the column cut-out switch does not inhibit MCAS).

 

2.  When the pilot stops operating the elec trim switch, MCAS "waits" for several seconds before starting a new down-trim order.  What's the reason for the delay?  I can't believe it's to allow sensors to "settle down" after a transient.

 

Both of these design/implementation features seem to me to add cognitive workload to pilot in recognizing trim "runaway" (which isn't really running away).  As pilots have pointed out, other systems also operated on trim, such as STS so you have to evaluate unwanted "MCAS" trim in a noisy  (as in, aircraft is moving the stab up or down for other reasons) environment.

 

scott s.

.

 

 

 

That is how I have come to feel too Scott, but I do not know much about these systems other than what I have read in my thread so I just have to learn and let it be.  It just seems like a "middleman" has been incorporated into flying an aircraft and it reminds me of WALL-E and the fight with AUTOPILOT in that movie.  The movie was so funny because automation with feeling was accepted in the end to a lesser extent, and the last scene you can hear faintly the Star Wars intro when we first see Luke on Tatooine, which also is hidden in the Harry Potter theme and I laugh about the cleverness of John Williams when I think of his touch on these modern classics over the years.  But I digress, I have a growing concern about automation increasing, rather than decreasing, the workload on pilots. 

There needs to be a happy medium.  In real life, and in sims, I find flying easiest when my brain is allowed to handle things, not electronics. You ask ATC (if in controlled airspace) for the clearances you need and you fly.  Yet I feel pilots are being controlled too much now, in an effort to make flying perfect, a long void of airline accidents seems to be on the rise again.  Pilots, ATC and aircraft ground crew, flight crew and designers need to have a scrum, without too much government interference, to make flying safer.  Then there are simply accidents, part failures from metal fatigue, we need to take the old aircraft gradually out of the inventory, recycle them, and use them again in new aircraft as best we can. 

With vicarious travel now possible thru the Internet, connectivity possible thru video apps like Skype (my happiest Christmas was when I set up a Skype video conference with my in laws in Mexico, they loved me for being an IT guru), travel will reach a steady rate and grow no further, and there will be less need for airliners in the sky, except for tourism which we will always want, for those countries that accept us and let us in to exchange our cultures.  Air travel is still in my opinion the safest way to get around when you use it for its purpose, about 300+ miles or more, about the endurance of most average driving vacations.  Or for hopping oceans, I dream of seeing the Middle East someday with its beautiful architecture, Saudi Arabia would be my first stop, or Iran if the country opens to tourism again some day.

Men and women have built great beauty in our world out of devotion to each other, and those who have gone before them that they think about, their parents and forebears. 

Just like we honor all those pilots who in a little more than one hundred years have shown us a world of beauty we did not know exist.

Everyone has a Higher Power and Pilots, those who dreamt of bringing our world together with flight, are my Higher Power. 

John

[G-RFRY 1,712]

Did Boeing explain to airlines only put highly skilled and exceptional pilots in this aircraft before they took there orders and money, if not this could be very expensive for them. There's a report that the same aircraft had a problem the before and a pilot passenger sitting in the cockpit spotted what was happening when it nose dived and told them to disable AP while they were struggling with the controls. 

[KevinAu 441]

10 hours ago, Bert Pieke said:

That is what is reported for the Lion Air flight.. did the Ethiopian flight also have a malfunctioning AoA sensor?  And if so, why did the crew not recognize it?    The Lion Air crash got lots of publicity... so they must have been aware..

No one knows yet. The recorders are probably only just being read out now. This is why the grounding when it started, can be considered a ‘jump to conclusion’. When the FAA finally grounded it, they cited they had finally seen some ads-b type data on their flight profile which showed similarities to lion air. But when china first announced and all the other countries followed, there was no evidence at all except for media speculation. After thr grounding, it was announced that the tail jack screw was found in the full nose down trim position. The conclusion is probably right, but it was achieved without any evidence.

[IUBrian 151]

3 hours ago, KevinAu said:

No one knows yet. The recorders are probably only just being read out now. This is why the grounding when it started, can be considered a ‘jump to conclusion’. When the FAA finally grounded it, they cited they had finally seen some ads-b type data on their flight profile which showed similarities to lion air. But when china first announced and all the other countries followed, there was no evidence at all except for media speculation. After thr grounding, it was announced that the tail jack screw was found in the full nose down trim position. The conclusion is probably right, but it was achieved without any evidence.

I don’t necessarily disagree that the grounding was without physical evidence, but two crashes of the same model of a new plane under similar circumstances is a statistical anomaly, and an extremely statistically unlikely occurrence. That in and of itself is a type of evidence.

 

By way of analogy, legally, in criminal law, there is a similar type of evidence, under the Federal Rules it’s rule 404(b), and most states have similar rules - it’s an exception to the general principal that in prosecuting someone you cannot bring up evidence of prior misconduct; a jury is supposed to decide guilt or innocence based upon the facts of an individual case, not what the defendant may or may not have done in the past. One exception is if the past incidents are of a unique nature that could be described as a “signature” crime. This is epitomized (prior to the rules of evidence) by a turn of the 20th century case known as the “Brides of the Bath” (worth a google search). Basically a man was married three times, all wives allegedly drowning in a bath tub. There was little if any physical evidence to establish that the husband had murdered his wives, but due to the extremely unlikely probability that 3 wives would die in the same unusual manner the prosecution was allowed to introduce the deaths of his prior wives in the prosecution for the murder of the third. 

In that sense I’d say that the nature of the two crashes is evidence. Again, to use a legal analogy, maybe not enough to establish “guilt beyond a reasonable doubt,” but “probable cause” to justify grounding. 

Edited March 20, 2019 by IUBrian

[Bobsk8 12,726]

I think what the world is realizing now, and some US politicians is that Boeing and the FAA are working together and their primary goal isn't safety anymore.

[Murmur 3,941]

22 hours ago, skelsey said:

To explain further:

This all comes about because of a certification issue: specifically FAR 25.173 which deals with static longitudinal stability.

(my emphasis).

As I understand it, this is where the Max encountered issues during flight test. Without MCAS, the Max does not meet the requirements.

I wonder, instead of using stab trimming, wouldn't it be simpler (and safer) to use artificial feel on the yoke to meet the gradient force requirements? Or maybe 737 controls are reversible ones with no artificial feel?

[JRBarrett 3,070]

1 hour ago, Murmur said:

I wonder, instead of using stab trimming, wouldn't it be simpler (and safer) to use artificial feel on the yoke to meet the gradient force requirements? Or maybe 737 controls are reversible ones with no artificial feel?

The artificial feel system is designed to increase the stick force required for a given control surface deflection as airspeed increases. To make it operate in its intended manner in an actual stall scenario, where airspeed would actually be rapidly decreasing would not be possible without completely redesigning the AF system. 

The MCAS-induced application of nose-down trim would be entirely appropriate if the aircraft truly was on the verge of a stall. The problem, of course, is that if it activates at the wrong time due to faulty sensor data, it will have the effect of putting the aircraft in a dive that may not be recoverable at low altitude if the system is allowed to run the trim to full nose down - and the current implementation of MCAS appears to have that ability.

It would be like having a system that would automatically deploy the landing gear at 500 feet AGL if the aircraft was fully configured for approach, but the pilots had forgotten to put the gear down. In that scenario, it could be a life saver. But, if a malfunctioning sensor caused the gear to suddenly deploy while in a Mach 0.80 cruise at FL350, the results could be disastrous.

The two major engineering fails with MCAS appear to be that it will activate based on the input of only one AOA sensor, (even though two sensors are installed on the aircraft) - and even more serious, the fact that it has no “memory”. It will apply 2.5 degrees of nose-down trim the first upon first activation, but if the pilot counteracts that by trimming in the opposite direction with the trim switch on the yoke, MCAS resets and applies an additional 2.5 degrees of trim each time it subsequently activates. Apparently there is no “sanity check” where MCAS would look at how much trim has already been applied, or how many times it has previously activated.

Even my Keurig coffee maker has more “sense” than that. It won’t run the brew cycle twice (potentially overfilling the cup) - it has to be reset by installing a new container of coffee, and putting an empty cup below the fill spout before it will activate a new brew cycle.

The proposed Boeing software fix is supposed address both issues: reliance on only one of the two AOA sensors, and multiple activations - but that is far too late for the hundreds of people who have lost their lives.

 

 

[Bobsk8 12,726]

Apparently one plane that crashed almost crashed the day before, and was saved from crashing by an extra pilot that was present.  https://www.cnn.com/2019/03/20/asia/lion-air-third-pilot-intl/index.html

Edited March 20, 2019 by Bobsk8

[threexgreen 3,139]

22 hours ago, John_Cillis said:

I have to wonder though, why all this was added to the MAX.  What else does this automation do?  Does it improve efficiency in some way or does it improve stresses on the airframe in some way?  There must be some purpose for these improvements

As has been explained numerous times in this thread, the purpose of MCAS is to make up for the increasing nose up momentum at high AoAs caused by the lift that the engine nacelles produce, so that the pilot while approaching a stall keeps pulling back on the yoke until it's fully aft when the stall occurs instead of releasing backpressure and even applying nose down input.

 

20 hours ago, scott967 said:

1.  Why the MCAS is inhibited when pilot operates the elec trim switches on the column.  I assume the idea was the "pilot knows what he is doing" (but the column cut-out switch does not inhibit MCAS).

The idea is, like you say, that the pilots can counteract the MCAS commands in case it's activated erroneously, just like what happened in the Lion Air crash. What I assume the repeated inputs are for is for the MCAS to kick in in case the aircraft slips into a secondary stall upon recovery. With the AoA sensor still sending data suggesting the aircraft is still in a stall the MCAS kicks in again and again and won't stop because the faulty data won't stop being sent. Unless you use the stab trim cut out switches you can't stop MCAS and eventually you won't be able to fight back anymore because of the dive the aircraft is now in.

 

7 hours ago, Murmur said:

I wonder, instead of using stab trimming, wouldn't it be simpler (and safer) to use artificial feel on the yoke to meet the gradient force requirements? Or maybe 737 controls are reversible ones with no artificial feel?

In order to meet certification requirements, when the aircraft is put into a stall, the pilot needs to be able to do that by pulling back until the yoke is fully aft when the stall occurs. While doing this, the AoA has to increase at a steady rate. The MAX exhibits a different behaviour. The lift created by the engine nacelles makes the nose move up faster close to the stall AoA, hence increasing the rate at which the AoA increases. To keep a steady rate the pilot now has to release pressure on the yoke and move it forward and thus can't have it fully aft when the stall occurs. The MCAS kicks in and applies nose down stab trim to counter the increased nose up momentum so that the pilot can keep pulling and eventually have the yoke fully aft with the elevators fully deflected nose up. If you just add artificial feel to the yoke you won't stop the increased nose up momentum caused by the lift created by the engine nacelles.

Edited March 20, 2019 by threegreen

[scott967 62]

I found this thread found here

to be the best in understanding MCAS

 

scott s.

.

 

[John_Cillis 2,406]

3 hours ago, threegreen said:

As has been explained numerous times in this thread, the purpose of MCAS is to make up for the increasing nose up momentum at high AoAs caused by the lift that the engine nacelles produce, so that the pilot while approaching a stall keeps pulling back on the yoke until it's fully aft when the stall occurs instead of releasing backpressure and even applying nose down input. 

 

The idea is, like you say, that the pilots can counteract the MCAS commands in case it's activated erroneously, just like what happened in the Lion Air crash. What I assume the repeated inputs are for is for the MCAS to kick in in case the aircraft slips into a secondary stall upon recovery. With the AoA sensor still sending data suggesting the aircraft is still in a stall the MCAS kicks in again and again and won't stop because the faulty data won't stop being sent. Unless you use the stab trim cut out switches you can't stop MCAS and eventually you won't be able to fight back anymore because of the dive the aircraft is now in.

 

In order to meet certification requirements, when the aircraft is put into a stall, the pilot needs to be able to do that by pulling back until the yoke is fully aft when the stall occurs. While doing this, the AoA has to increase at a steady rate. The MAX exhibits a different behaviour. The lift created by the engine nacelles makes the nose move up faster close to the stall AoA, hence increasing the rate at which the AoA increases. To keep a steady rate the pilot now has to release pressure on the yoke and move it forward and thus can't have it fully aft when the stall occurs. The MCAS kicks in and applies nose down stab trim to counter the increased nose up momentum so that the pilot can keep pulling and eventually have the yoke fully aft with the elevators fully deflected nose up. If you just add artificial feel to the yoke you won't stop the increased nose up momentum caused by the lift created by the engine nacelles.

" As has been explained numerous times in this thread, the purpose of MCAS is to make up for the increasing nose up momentum at high AoAs caused by the lift that the engine nacelles produce, so that the pilot while approaching a stall keeps pulling back on the yoke until it's fully aft when the stall occurs instead of releasing backpressure and even applying nose down input. "

Please relax and bear with some of us, there are so many replies in this thread, some speculative and some not, that it is hard to weed thru them all.  I did find a good media report on CNN which describes the MCAS as you do, so it sounds like the media is getting better educated and reporting things more clearly.  They mentioned the day before, which has probably already been mentioned in this thread, that a deadheader had to help recover the same aircraft from the same situation, or so the report says.

I still believe some of this automation is unneeded, takes pilot control away by increasing the reaction time needed to overcome the automation.  Tens of thousands of previous gen 737 flights have proven it was fine without the MAX's automation, unless the MCAS was installed on those aircraft, again something probably already discussed and answered somewhere in this thread.  Add to that, tens of thousands of other flights, on other aircraft, in the years before automation really kicked in.  However I was on an L1011 that autolanded at JFK, in clear but windy weather, when I was on my way to Europe in '94.  The landing was a bit bumpier than usual, the pilot apologizing prior to the landing, but for some reason they chose to autoland.

On a side note, when I was training the former JFK Hilton which faced the north side of the airport, I heard a much louder approaching aircraft than usual and had the pleasure of seeing the Concorde fly by my room.  My client graciously gave me a room on their highest floor when I told them my love of aviation.  Their hotel was busy round the clock as airport hotels are, it was why I was sent there, we called it a Cat 5 client and I had two employees to help me.  I allowed them to leave two weeks early when my client asked me to stay on and write some reports in Crystal reports for their accounting and housekeeping staff, so I worked with their chain's CIO in his apartment (with his cute girlfriend flirting with me, a very married man).  They wanted to hire me but I could not move my wife and newborn daughter to New York, even at double my income they offered my living expenses would have gone up by a factor of 4 from Phoenix.

The client kept asking me two days before I was to fly out of there for my next gig in Seattle, the day after Christmas, what airline I was flying on.  My boss (who is currently developing an electric PAV I have been invited to fly) warned us not to share that information as some clients were known to cancel or change our flights to keep us longer at our expense.  But I told them anyway, and to my pleasure when I flew home on Christmas Eve, I found that thru their close relationship with the CEO of America West, I had been upgraded to First Class.  Did I enjoy it?  For about twenty minutes, lol, then I was fast asleep until just outside of Phoenix.  It was that Champagne, the curse of every first class passenger.  One drink and an 8000 foot cabin altitude and I was a goner.

John

[IUBrian 151]

1 hour ago, scott967 said:

I found this thread found here

to be the best in understanding MCAS

 

scott s.

.

 

The side by side photo comparing the original 737 model is stunning; it really puts it into perspective, quite literally

[John_Cillis 2,406]

11 minutes ago, IUBrian said:

The side by side photo comparing the original 737 model is stunning; it really puts it into perspective, quite literally

I notice less side visibility in the pilot's office, wonder why they decreased that.  Aren't pilots supposed to be spatially aware of traffic, the better the vis the safer the flying for the pilots.  My CFI always told me to keep an eye outside the aircraft, but it seems modern commercial aviation is becoming more and more a chore in the pilot's office and more aircraft management than flying these days.  Arguably it could be said aviation is safer but is there going to be a trend to obsolete the pilot altogether?  I thought there was a pilot shortage in the commercial aviation industry.  I know these are sensitive questions out of respect for those who know more than us pilots with a GA or Light Sport or ultralight background have, so please bear with us.

John

[Bobsk8 12,726]

45 minutes ago, John_Cillis said:

I notice less side visibility in the pilot's office, wonder why they decreased that.  Aren't pilots supposed to be spatially aware of traffic, the better the vis the safer the flying for the pilots.  My CFI always told me to keep an eye outside the aircraft, but it seems modern commercial aviation is becoming more and more a chore in the pilot's office and more aircraft management than flying these days.  Arguably it could be said aviation is safer but is there going to be a trend to obsolete the pilot altogether?  I thought there was a pilot shortage in the commercial aviation industry.  I know these are sensitive questions out of respect for those who know more than us pilots with a GA or Light Sport or ultralight background have, so please bear with us.

John

Both Airbus and Boeing are working on pilot less aircraft. The one of the  largest expenses in aviation are pilots salaries. Currently the pilot for the most part, flies the aircraft up to about 600 feet , AP on, and from then on automation does the rest of the trip including landing. They are thinking that maybe in 10 years or even less, the aircraft will fly itself.