MAX’s Return Delayed by FAA Reevaluation of 737 Safety Procedures Mk II

[OldnGrounded]

Originally Posted by medod

Whatever the exact reasons, the MAX’s big ass engines mean it fails 25.255 without MCAS.

Yup. That's it.

That is why I believe the MAX will never fly again in commercial service with less than three AoA vanes.

There is, at least, a serious argument that it shouldn't (or without some synthetic third AoA input).

[jimtx]

[QUOTE=Grebe;10645167]The length of this thread and its previous makes it difficult to refer to specifics and what the past and current semi- technical discussions have been- since most of the current questions have long since been addressed- discussed- ad naseasum

So I'm going to post a few links to different blogs- which if 0ne takes the time to read and figure out how to go to previous and following on the site(s) listed will at least provide mostly rational discussion.

https://www.satcom.guru/2019/10/flaw...-disaster.html

https://leehamnews.com/2019/11/29/bj...-crash-part-5/


https://www.moonofalabama.org/2019/0...g-737-ngs.html



B737 Max threads


And from a long ago post somewhere in prune news and rumours one can find the below






And re stick force found

https://www.satcom.guru/2019/03/taki...aiting-on.html

........ This aspect is essential in ensuring the pilot does not have to push the yoke to stop the plane from pitching up, which violates positive stick force per g as required in 25.255....

... stick force per g must be positive . ..

I think the slope of the stick force per G is positive. It's just not linear in the regime they are concerned with.

[Loose rivets]

Fitting a third vane?

You can see how hard it would be to add another AoA vane. It must not disturb the other sensors and they must not disturb it. When a good place is found in airflow analysis, there's probably a complex object behind the metal. When a final decision is made, the wiring to the black box will be a major undertaking when multiplied by the hundreds of existing MAX's.

When the wiring is in, the black box will not have the slightest idea what to do with the information. It has no plughole labelled 'Additional Sensors'. I have a bad feeling it would not even have the capability of being modified to take a new input. You can see where this is going: not a chance of Boeing accepting this mod without one hell of a fight. AoA synthesis would be easier, and then, that information has to go somewhere.

Picture pulled off a Seattle Times post from October. It says MAX, but not sure. However it allows my point to be made.

[OldnGrounded]

[QUOTE=jimtx;10645212]

Originally Posted by Grebe

I think the slope of the stick force per G is positive. It's just not linear in the regime they are concerned with.

Here it is:

§ 25.255 Out-of-trim characteristics.

[. . .]

(b) In the out-of-trim condition specified in paragraph (a) of this section, when the normal acceleration is varied from + 1 g to the positive and negative values specified in paragraph (c) of this section -

(1) The stick force vs. g curve must have a positive slope at any speed up to and including VFC/MFC; and

(2) At speeds between VFC/MFC and VDF/MDF the direction of the primary longitudinal control force may not reverse.

[DieselOx]

I think the slope of the stick force per G is positive. It's just not linear in the regime they are concerned with.

Why do you think that? I hear a lot of people speculating that's the case, but no one has has definitively proven that one way or the other, directly from any data so far publicly available.

Boeing's statement is basically MCAS is an augmentation to maintain proper stick force, but as far as I remember, reading everything here and everywhere else, they very carefully never say where they start from.

Someone fly the plane w/o MCAS and report back. Then I'll believe it.

[Pilot DAR]

I was right, and then left seat, for Transport Canada Aircraft Certification flight testing yesterday. The test pilot and flight test engineer, were extremely thorough. The FTE explained to me after the day's test flying that because of the concern that some compliance was not truly demonstrated for the MAX certification, Transport Canada was not going to allow themselves to be caught out not having thoroughly flying tested one of their programs, if another authority later inquired.

At least, with Transport Canada, the pendulum has swung back (and I suspect with EASA too). Where, in the past, they might have accepted my word as an aircraft certification delegate, now they want to see for themselves, 'cause they're on the hook for documenting the finding of compliance. Considering the MAX certification concerns, I can certainly see their point!

[averow]

You are correct Murphy. I use three alarms in different devices for critical events (like getting to work on time.) I haven't been late for twenty years now, and yes my colleagues notice.

[jimtx]

Originally Posted by DieselOx

Why do you think that? I hear a lot of people speculating that's the case, but no one has has definitively proven that one way or the other, directly from any data so far publicly available.

Boeing's statement is basically MCAS is an augmentation to maintain proper stick force, but as far as I remember, reading everything here and everywhere else, they very carefully never say where they start from.

Someone fly the plane w/o MCAS and report back. Then I'll believe it.

I would agree that Sully should fly the plane without MCAS and report back. I'm sure the Boeing test pilots have been fitted with a chastity belt and you won't hear anything from them about their opinion about whether the airplane should not be flown without MCAS. I'm assuming that the "§25.175 Demonstration of static longitudinal stability." requirements of a "stable" (what most of us were calling linear) stick force curve were not met in flight test in rarely visited flight regimes and they thought they had to pencil whip that. I would have argued about what was a stable stick force curve if I thought the bare airframe would not give a normal pilot any trouble. They decided to pencil whip it rather than bite the bullet and are continuing to let the tail wag the dog. But I'm with you, we are babes in the woods until Boeing and FAA clear up some stuff.

[Nomad2]

You know, Boeing clearly have the expertise and experience to build the best passenger jet in this sector of the market, so why have they persisted all this time with ever more modified 737s?

Plainly, the original design was good, and it could stand some enlargement, but with any design there comes a point where the possibilities for modification and improvement are exhausted. Looking at some of the larger NGs or the P-8 shows how far they came- and safely.

But adding the LEAP engines was clearly a step too far. The 737 really needed a redesign into what would effectively be a new aircraft to accommodate the new engines, so why wasn't it done?

If this jet is to return to the skies, it should get what it needs- new undercarriage, probably the wing repositioned on the fuselage, the engines where they should be, and many other changes. It will be too much of a change for the existing jets, but the MAXes could probably be modified into useful 737 variants using normal engines.

Boeing need to get a grip. There's more to a company than just money and profit- there's also product.

They should do what they know, better than anyone, needs done.

Accept the sunk losses, repurpose the MAXs' into something else.

Start on their A320, GTF engined competitor from scratch, restore their reputation, and make a damn good job of it.

Go on to sell thousands of them, and make a fortune.

edit. The MAX has LEAP engines, not GTF. Although both are much bigger and powerful than previously fitted power plants.

[Grebe]

Originally Posted by Nomad2

You know, Boeing clearly have the expertise and experience to build the best passenger jet in this sector of the market, so why have they persisted all this time with ever more modified 737s?

Plainly, the original design was good, and it could stand some enlargement, but with any design there comes a point where the possibilities for modification and improvement are exhausted. Looking at some of the larger NGs or the P-8 shows how far they came- and safely.

But adding the GTF engines was clearly a step too far. The 737 really needed a redesign into what would effectively be a new aircraft to accommodate the new engines, so why wasn't it done?

If this jet is to return to the skies, it should get what it needs- new undercarriage, probably the wing repositioned on the fuselage, the engines where they should be, and many other changes. It will be too much of a change for the existing jets, but the MAXes could probably be modified into useful 737 variants using normal engines.

Boeing need to get a grip. There's more to a company than just money and profit- there's also product.

They should do what they know, better than anyone, needs done.

Accept the sunk losses, repurpose the MAXs' into something else.

Start on their A320, GTF engined competitor from scratch, restore their reputation, and make a damn good job of it.

Go on to sell thousands of them, and make a fortune.

If this jet is to return to the skies, it should get what it needs- new undercarriage, probably the wing repositioned on the fuselage, the engines where they should be, and many other changes. It will be too much of a change for the existing jets, but the MAXes could probably be modified into useful 737 variants using normal engines

Sorry Charlie - doesn't work that way in real airplanes.....

[Superpilot]

When the wiring is in, the black box will not have the slightest idea what to do with the information. It has no plughole labelled 'Additional Sensors'. I have a bad feeling it would not even have the capability of being modified to take a new input.

It is possible to daisy chain data. There does not need to be a one to one relationship between sensor and input. You simply offset the values from one sensor by a known constant so it can be decoded later (in software) as coming from a separate source. This would be a major weight saving too. Acceptable to the FAA? Who knows...

[fizz57]

Originally Posted by DieselOx

Why do you think that? I hear a lot of people speculating that's the case, but no one has has definitively proven that one way or the other, directly from any data so far publicly available.

Boeing's statement is basically MCAS is an augmentation to maintain proper stick force, but as far as I remember, reading everything here and everywhere else, they very carefully never say where they start from.

Someone fly the plane w/o MCAS and report back. Then I'll believe it.

The non-linearity issue was brought up by FCEng84 way back when the whole thing started in one of the now-closed threads. It is the stick force reversal and instability that are speculations, and came later.

That poster was usually a very reliable and well-informed source. Unfortunately he hasn't posted for a very long time (probably the price for being too well-informed).

[MechEngr]

Originally Posted by Nomad2

You know, Boeing clearly have the expertise and experience to build the best passenger jet in this sector of the market, so why have they persisted all this time with ever more modified 737s?

Plainly, the original design was good, and it could stand some enlargement, but with any design there comes a point where the possibilities for modification and improvement are exhausted. Looking at some of the larger NGs or the P-8 shows how far they came- and safely.

But adding the GTF engines was clearly a step too far. The 737 really needed a redesign into what would effectively be a new aircraft to accommodate the new engines, so why wasn't it done?
...

Because that's not what their customers wanted. They wanted a 737 that their pilots could easily move to, that their gate equipment would work with, that their mechanics were qualified to work on and had experience working with. A ground-up new airplane would have none of that, particularly if the landing gear got longer. If that's not what they wanted the purchasing airlines could go with Airbus and start some segments of their business from scratch.

It's not clear the new version is a step too far. A lack of imagination seems to have prevented anyone from noticing the potential for disaster, even after the first crash when all the variables were laid out, plain to see. This is the first foray into a semi-aided system for a generally manually controlled plane. Unlike FBW, it doesn't require scrutiny of every detail of its function merely to fly. The autopilot was essentially unaffected by the engine change and defers to the pilots when a problem happens. MCAS sits in a similar position to the driving systems being used on cars that keep lanes and try to avoid collisions; they work but, since they depend on the operator, when there's an overlap of authority there's a much more complex potential interaction.

[Bend alot]

Originally Posted by MechEngr

even after the first crash when all the variables were laid out, plain to see.

Cummon - plain to see!

There are still many secrets - after the first crash very little was disclosed and what was was in tongues in the FAA AD that lacked much information that could have been included.

Something like we expect more than 10 aircraft to crash over the next thirty years due to the MCAS system, based on known information relating to the first crash.

[MechEngr]

Originally Posted by Superpilot

It is possible to daisy chain data. There does not need to be a one to one relationship between sensor and input. You simply offset the values from one sensor by a known constant so it can be decoded later (in software) as coming from a separate source. This would be a major weight saving too. Acceptable to the FAA? Who knows...

The sensor is a resolver which itself is has multiple transformers. They have a precision circuit to drive them and a complicated circuit to read them. They aren't capable of being daisy chained as the processing is done in the ADIRU, which has one input for that resolver. Look up how a position resolver is operated; they are a nearly ideal sensor with no wear components required and no friction from making measurements, unlike potentiometers, and continuous readings, unlike encoders. They make up for it in the support electronics, though they can be used in a selsyn configuration, which can be useful for remote analog sensing, though synchros are more likely to be used as selsyns..

[Nomad2]

Grebe.
It may not be how things happen at Boeing, North America- but it's exactly how things DO happen at Boeing Brazil.
The GTF engined 190 E2 has a new undercarriage, with a repositioned wing, the engines where they should be, and many other changes- so maybe it's about time things changed in the US, Charlie?

MechEngr.
The Embraer 190 E2 carries a common type rating with the original E190, despite being effectively a completely different aeroplane and properly redesigned to accommodate the fuel efficient (and jolly powerful) GTF motors.
I agree, that's what the customers want....
What they probably didn't want is a re-engined 737 that they are not permitted to operate.

[MechEngr]

Originally Posted by Bend alot

Cummon - plain to see!

There are still many secrets - after the first crash very little was disclosed and what was was in tongues in the FAA AD that lacked much information that could have been included.

Something like we expect more than 10 aircraft to crash over the next thirty years due to the MCAS system, based on known information relating to the first crash.

That report came out while Boeing was working on new software to describe what would happen if the full fleet, about 10X more planes, with unchanged software, were to fly. Same thing happens when a car recall is made; but the predicted result never happens because most cars get the recall done and the rest get taken out of service for some other reason. Since 100% of the planes were intended to get the 'recall' done to update the software the report was a gross, though necessary, exaggeration.

What information available now was not in the preliminary Lion Air report that made a difference? The Emergency Airworthiness Directive and associated AD does not leave much to the imagination, and anyone flying a Max should have read that preliminary accident report as if their life depended on it. In addition Boeing issued their own guidance directly to Max operators, with further details, such as that it operates only in flaps-up flight. They also issued a separate bulletin, number TBC 19, that described the 10 second run and then retrigger on any trim change with a 5 second delay.

The only secret that is left is that if the maximum velocity is exceeded with the plane far out of trim that the trim wheels are too hard to turn. But if the initial guidance is used, the plane is never out of trim and never outside the velocity envelope, so planning for that is unexpected.

I'd say it was up to every operator to carefully examine all the data about a crash involving their same type equipment and understand whether their training and other preparations were sufficient to deal with the situation. Had that happened the difficulty in using the trim wheels might have been exposed; certainly Mentour Pilot did his part and CP Bernd Kai von Hoesslin seems to have fought hard to do so as well, but it didn't seem to occur to Max operators to push back and go public with any flaws in the published documentation.

[Bend alot]

MAX operators just like the shinny brochure parts.

The FAA AD on the matter was and is absolute rubbish, of the same level of the original certification of the MAX - just how Boeing told them it will say.

The FAA does not have a massive credibility issue for non genuine reason/s. They blew it during the start, after the first accident, after the second and now the non reply to the Freedom Of Information request - that request was excluding the FAA and its discussions and decisions documents. It was a genuine request that if nothing to hide would have gone along way to regaining public trust.

I went to the local mint the other day and said I am a customer I buy your gold bars but they are too small. I will remain a customer if you make them bigger, but you must not be more expensive than the local bank. That's what customers want.

P.S. given half the pilots did "unexpected" things in the MAX test sims the other day with all the 20/20 of the last year - The prelim report and the AD were based on incorrect assumptions for many/most crews.

[MechEngr]

Originally Posted by Nomad2

Grebe.
It may not be how things happen at Boeing, North America- but it's exactly how things DO happen at Boeing Brazil.
The GTF engined 190 E2 has a new undercarriage, with a repositioned wing, the engines where they should be, and many other changes- so maybe it's about time things changed in the US, Charlie?

MechEngr.
The Embraer 190 E2 carries a common type rating with the original E190, despite being effectively a completely different aeroplane and properly redesigned to accommodate the fuel efficient (and jolly powerful) GTF motors.
I agree, that's what the customers want....
What they probably didn't want is a re-engined 737 that they are not permitted to operate.

Not sure where you are going with this. The E190 customers aren't 737 customers. Looks like there are under 600 190s in the world and orders for less than 40 E2s so far.
There are about 7000 NGs and were orders for about 5000 Max's. That's one to two orders of magnitude greater investment in 737 operations.

I see it's a FBW which covers a multitude of sins, so the comparison to the 737 is weak. " The E2 have 75% new parts" which would cripple logistics for an airline that had thousands of the old ones to maintain and were looking to expand with new ones; not a problem for the E190 series. (quote per the Wikipedia E2 page)

It would have been an impossible sell for Boeing to make a plane that did not fit existing operations. I guess we'll see if Embraer can sell in quantity.

[MechEngr]

Originally Posted by Bend alot

MAX operators just like the shinny brochure parts.

The FAA AD on the matter was and is absolute rubbish, of the same level of the original certification of the MAX - just how Boeing told them it will say.

The FAA does not have a massive credibility issue for non genuine reason/s. They blew it during the start, after the first accident, after the second and now the non reply to the Freedom Of Information request - that request was excluding the FAA and its discussions and decisions documents. It was a genuine request that if nothing to hide would have gone along way to regaining public trust.

I went to the local mint the other day and said I am a customer I buy your gold bars but they are too small. I will remain a customer if you make them bigger, but you must not be more expensive than the local bank. That's what customers want.

P.S. given half the pilots did "unexpected" things in the MAX test sims the other day with all the 20/20 of the last year - The prelim report and the AD were based on incorrect assumptions for many/most crews.

Since there's no indication of what the current list is like or how they scored the performance of the pilots, however since every simulation was handled successfully, then it's possible the instructions are now so detailed they required more time to memorize than was given.

The gold bar analogy is terrible, but it is right - if the mint can do that they will undersell the competition; that's how the market generally works.

The AD is not issued in a vacuum. It does not include a complete how-to training course in learning to trim a plane. That was assumed to be trained into pilots, but it is clear the Ethiopian pilots did not do this and it is unclear why they did not do this. They did, however, ignore the clear admonition to never turn the trim enable switches back to enable if they had been disabled. The AD covered that and that allowed the last trim application the pilots did not counter.