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Boeing 737 MAX+

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Re: Boeing 737 MAX+

Postby Paphitis » Fri Mar 29, 2019 3:53 pm

I'm not convinced at all that the MCAS has done anything other than do EXACTLY what it's designed to do.

It's suppose to pitch the aircraft down when a stall is imminent, to try and keep the aircraft flying. I defer to the full report because I have not had the time to stay up to date with this.

SAS Systems will pitch the aircraft down in a stall. On a short final, this has a strong potential to be fatal. But a stall is also 100% fatal. There will be no survivors in a stall. If the aircraft is to survive a SAS event (MCAS) will depend on how high the aircraft is off the ground and if there is enough time for the pilots to recover.

The only clear thing for me at this point is that the pilots were not trained to deal with this (MCAS) after they stalled the aircraft.

MCAS does what it is designed to do. It will pitch the aircraft down to prevent a stall. The pilots were not trained how to disengage it or on what to do when it engages. Question is, who is responsible for that, Boeing or Ethiopian? or are they jointly responsible? Did Boeing neglect to provide adequate training or was Ethiopian negligent?

Also, questions need to be asked how the pilots entered a flight condition resulting in the MCAS engaging (how they entered a stall flight condition). What factors contributed to this. That's the big elephant in the room. MCAS would not engage without the aircraft entering into a stall flight condition. MCAS is in response to this flight condition so it can only be a contributing factor, not what was the outright cause of the crash.

Sorry but I can't see how Boeing is to blame here. Lawyers will be fighting over this for years to come. Boeing will not accept full liability I am pretty sure.

The full report will be out in 12 months times. That is when we will know. I am not going to speculate on bullshit in the meantime. Just don't trust the media because there is a lot of nonsense in circulation right now.

And Boeing will be a part of the investigation team because they have a right to be there along with the US Federal Aviation Authority, US ATSB and Ethiopian Aviation Authorities as well the countries who had their citizens on board the ill fated B737.
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Re: Boeing 737 MAX+

Postby Robin Hood » Fri Mar 29, 2019 4:16 pm

Londonrake wrote:https://www.telegraph.co.uk/news/2019/03/29/boeing-anti-stall-sytem-caused-ethiopia-crash-strongest-link/

.


Interesting ..... but when you have finished reading it you are no more clued-up on WHAT the problem was. Even so, it seems to be a design/engineering problem that the pilots had no control over at all. They needed to be aero design engineers, members of the design team, know all the design parameters and have been at all the project safety review meetings to realize the problem ..... and even then it appears the only remedy was to pull the circuit breaker on the MCAS system. Not exactly a job you would expect a pilot to perform.

Pilots fly aeroplanes, they are not engineers! In fact when it comes down to it, they don't actually fly the aeroplane ...... the computers do! A pilot inputs data ..... the computers respond to that data. An aircraft designer will build in limits and features into the software to prevent the computers from responding to data that is invalid. That is also why they have three parallel systems and vote two-out-of-three ...... the system will always go for the majority decision and the possibility of all three systems having the same software error is almost impossible.

So, a computer is only as good as the data it is given. If it computes that the data is valid, it responds to it. But it needs multiple inputs from multiple sources to be able to make the decision. 'WHAT IF' .... a common expression in a design review, especially a safety review. What if the sensor was feeding a false figure in certain conditions? Paphitis has demonstrated just how much he relies on the electronics to perform his job if he has to fly the aircraft in 'MANUAL' and even then he can't do it without the computer systems. :roll:

I will put my money on it being an overlooked 'what if' and it only became obvious AFTER the event(s). :(
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Re: Boeing 737 MAX+

Postby Paphitis » Fri Mar 29, 2019 4:23 pm

Yes, pulling circuit breakers is EXACTLY what is expected of pilots.

We pull circuit breakers out all the time.

We have a QRH Manual with all the procedures for evry single system fitted to the aircraft. And yes, we have to pass Engineering Exams too as part of the endorsement on type.

The QRH is broken down to memory Item Checklists and Non Memory Items. We have 108 emergency and abnormal operations checklists, that cover off everything from Engine Failure, Engine Fire, Fuel Starvation, Ocean Ditching. Depressurization, and Stall Avoidance as well.

Memory Items are mandatory memory items that must be memorized. For instance, and Engine Fire has 6 memory items, and then we get the QRH checklist out to complete the checks.

There is NOTHING that isn't covered.

And as pilots we can draw schematics of our plane. We need to pass these exams and do yearly refreshers.

Memory items are practiced all the time in the simulator. We go over them again and again.
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Re: Boeing 737 MAX+

Postby Robin Hood » Fri Mar 29, 2019 4:25 pm

Kikapu wrote:Paphitis,

The creation of the MCAS for the 737 MAX is not the problem to get the aircraft out of a stall if the pilot is careless by putting the aircraft into a stall, but the problem is when the aircraft is no longer in a stall. Once the nose is forced down by the MCAS to get out of the stall, it won‘t allow the pilot to resume normal flight to level the aircraft, but instead, retains nose down attitude to the ground without some problem solving first by the pilots, by going through the operator‘s manual, which time may not allow when so close to the ground soon after take off.


I don't think you are that far off the truth. The problem from what I can find out was that the pilot had no means to overcome the problem ...... he would have needed to be an experienced engineer to do that. The MCAS seems to have been repeating the 'nose down' instruction process because the reading it was getting through a faulty sensor was telling it there was a stall condition when there wasn't one ...... and there was no ON/OFF switch! :?
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Re: Boeing 737 MAX+

Postby Paphitis » Fri Mar 29, 2019 4:31 pm

There are a number of ways to disengage the MCAS.

The issue is that the pilots entered into a flight condition that resulted in the MCAS engaging and they did not know how to disengage it.

The MCAS would disengage with lowering flaps (lowers the stall speed and disengages MCAS) and engaging the autopilot because the Autopilot prevents an excessive AoA and the Auto throttle will adjust power and speed.

There is also an ON/OFF switch. If the pilots disabled the Stabalizer Trim, the MCAS disengages. See photo. The pilots did not know this which friggin amazes me. It wouldn't happen in the company I work for in a million years. :shock:

So it boils down to this in my opinion.

1 How did the aircraft enter a stall flight condition? The only time I stalled a plane it was deliberate and I am sure that is the case for 99.9% of all pilots.

2. why were the pilots unfamiliar with this system? Name me an airline that would operate a plane that has MCAS and not train their pilots about this system. I can't fathom that.

MCAS only engages to correct an already present pilot error. So question is this, what caused the accident? Was it the MCAS or the initial pilot error? Subsequent questions (because there are always a number of factors), is whether or not the pilots were trained or knowledgeable about MCAS, and if not, why not.

The MCAS could easily be disengaged. It would not have been certified if that was not the case.
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Re: Boeing 737 MAX+

Postby cyprusgrump » Fri Mar 29, 2019 7:02 pm

Robin Hood wrote:
Kikapu wrote:Paphitis,

The creation of the MCAS for the 737 MAX is not the problem to get the aircraft out of a stall if the pilot is careless by putting the aircraft into a stall, but the problem is when the aircraft is no longer in a stall. Once the nose is forced down by the MCAS to get out of the stall, it won‘t allow the pilot to resume normal flight to level the aircraft, but instead, retains nose down attitude to the ground without some problem solving first by the pilots, by going through the operator‘s manual, which time may not allow when so close to the ground soon after take off.


I don't think you are that far off the truth. The problem from what I can find out was that the pilot had no means to overcome the problem ...... he would have needed to be an experienced engineer to do that. The MCAS seems to have been repeating the 'nose down' instruction process because the reading it was getting through a faulty sensor was telling it there was a stall condition when there wasn't one ...... and there was no ON/OFF switch! :?



Ignoring the normal waffle from the Koala... :roll:

My understanding is that Boeing were essentially trying to certify the MAX as a 50 year old 737 to save time and money.

The aircraft needed new, more powerful engines but they wouldn't fit in the existing mounting points (the 737 designed to be a low aircraft to ease ground handling) so new mountings were added forward of the old ones...

The new engine mounts disturbed the aircraft handling characteristics so software fixes were added...

The plane depended on a single AOA sensor to trigger MCAS resulting in nose down...

If the single sensor failed the pilots had just 40 seconds to fix a flight control system failure that they weren't told about before the aircraft was sent into an uncontrollable dive...

Pilots can extend 40 seconds by pressing a button on the control column which pushes up the nose...

In the Lion Air crash the pilots pushed the button 20+ times before diving into the sea...
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Re: Boeing 737 MAX+

Postby Robin Hood » Fri Mar 29, 2019 8:01 pm

Paphitis:
There is also an ON/OFF switch. If the pilots disabled the Stabalizer Trim, the MCAS disengages. See photo.


One question:

Where did you get that information from, that it also disengages MCAS ?

The photo shows the switch to operate the 'Stabilizer Trim' ..... not the Stabilizer ( :shock: Heaven forbid). As I understand it the MCAS operated on the Stabilizer not the trim tabs. Which would seem a reasonable assumption. The crew were in both cases fighting the MCAS that was pushing the nose down every 5 secs.(?) because it was seeing no recovery from the stall condition that the sensor was indicating.

...... and the pilots were unaware that they had an unmarked switch that would allow them to override the MCAS? That is hard to believe. :?:

Where can I find on the Internet, a schematic of the MCAS system?
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Re: Boeing 737 MAX+

Postby Kikapu » Fri Mar 29, 2019 11:33 pm

Well, it just came over the news, that there was no pilot error that caused an stall of the aircraft which would have activated the MCAS system, but instead, the MCAS activated itself prematurely, most likely by faulty information making the MCAS thinking there was an stall. As long as the faulty information kept on being fed to the MCAS, the longer the nose stayed down, all the way to the ground.
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Re: Boeing 737 MAX+

Postby Paphitis » Sat Mar 30, 2019 2:01 am

MCAS only works when the flaps are up. This is different to standard Stall Avoidance Systems that work in all configurations. The SAS on the plane I fly can activate in any condition. When you are on FINALS and you get the Stick Shaker, it scares the shit out of you. Had it once in the last 12 months on Finals in Sydney. That is a Stall Avoidance System like the MCAS. The MCAS has the same Shaker and Pusher system. You instinctively move the throttles forward and prepare for a Missed which in Sydney would cause extreme mayhem. It's one of the busiest airports in the world.

So in the B737 MAXI, MCAS disengages when the flaps are lowered. This is one way the MCAS can disengage.

The second way it can disengage is by turning the Stab Trims off. See above photo. This disengages the thumb control Stab Trim on the control column. See picture below.

The pitch of the aircraft can still be trimmed manually by rotating the trim wheel. See picture below.

Now, I don't read the media or listen to anything the media has to say about this crash or any other crash. The only thing I want to read is the preliminary report and the final crash report from the Official Investigation Team which comprises experts from Boeing, FAA, ATSB, Ethiopian Authorities and Authorities of some other countries that lost citizens (these are the ICAO rules) and the ICAO is an arm of the UN.

Even if there was a faulty sensor, the entire MCAS can be disengaged. People are getting too far ahead of themselves. There is a lot more going on here than just a faulty sensor or a rogue MCAS.

The Thumb Trim or Electric Stab Trim doesn't disengage MCAS. MCAS will keep over riding it till the Stab Trim is disengaged.
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Re: Boeing 737 MAX+

Postby Paphitis » Sat Mar 30, 2019 2:23 am

I am very selective of my sources. These sources are official sources.

Boeing issued an Air Directive (AD-2019-23-51) in December 2018 to all operators as part of a Flight Manual Amendment which outline the procedures to disengage the MCAS. This procedure covered off on the possibility of an erroneous sensor input. I do not know what this Air Directive replaced.

But all pilots would have been required to be trained in its implementation before flying the line. If necessary, the QRH on the Flight Deck and the Abnormal Checklists would have to be amended before the aircraft can be flown. This is what you would expect from most airlines around the world.

Boeing basically said, "oi you idiots, make sure you are following these procedures if you have a trim runaway (MCAS activation)".

Trim Runaway is a procedure in the QRH. Trims do runaway. Need to be able to disengaged and if that doesn't work the aircraft is grounded. TRIM STAB CUTOUT would be tested as a Pre-flight item. The way that is done is by activating the Electric Trim, noticing the spinning wheel forwards or aft and then switch to cutout should result in TRIM STOP. Plus, you need to check all trims for full travel, another requirement that can ground the aircraft.

This is straight from the B737 MAXI Manual.

https://cimg0.ibsrv.net/gimg/pprune.org ... c4cb07.jpg

Procedure is:

STAB TRIM Switches to CUTOUT
If runaway continues, hold the manual trim to arrest
Trim aircraft manually (using the Manual Trim Wheel)

Pilots would have also had continuous STICK SHAKER followed by Stick PUSHER in the stall until the MCAS was disengaged.

Stick Shaker is a pretty violent vibration and shaking of the Control Column. It's quite literally very pronounced and alarms go off too loud enough to grab your attention. All captured by the Flight data Recorder as well.
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