Posts: 2263
Joined: Wed Mar 01, 2006 4:29 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

patrickjp93 wrote:
patrickjp93 wrote:
Doppler is kid's play and is used to check density of weather systems. It's looking at resonant modes of light, not the turnaround time from particles a known distance away.

Special Relativity is the enveloping theory (and long since tested and proven) around how light interacts with objects in moving reference frames. The best way to understand how it is applied here is probably using the light speed train tunnel paradox. Because the speed of light does not change in a given set of conditions (in this case an air body's elemental composition and pressure) regardless of how fast its source is, you can use the difference in time for light to bounce back from a known distance to get your speed.

If you're running and throw a ball in front of you, the speed/velocity of the ball increases in the line you're traveling on above your running speed. However, this breaks down at the speed of light where it is impossible to exceed that speed. You running forward with a laser pointer in hand does not increase the propagation speed of the laser. Therefore, any change in time for a particle to leave the pointer and collide with what's in front of you and return which exceeds this absolute speed limit is your speed going in the opposite direction. That's why Special Relativity and Lidar can be used for this. Even radar can, but because it relies on some oscillatory modes to not come back as pure noise, it's probably easier to make such a system with Lidar.

OK. Just to make it clear - my PhD is in physics. And I know relativity a bit.
For the plane traveling at 3e2 m/s = 1e-6 c special relativity effects are in the noise. Lidar doesn't use relativistic effects.
So, try again.

I'm afraid Boeing (and a basic textbook) disagree with you, as they'll be using Lidar to detect turbulent flow up to 10 miles away, and the only way you can do that is detect multiple velocities of air streams simultaneously. https://www.aviationtoday.com/2018/03/2 ... onstrator/

You can claim to have a PhD, but that doesn't matter to me. Let's see you prove the argument rather than rest on your laurels.

You never mentioned clear air turbulence before. Turbulence is irrelevant to the converation anyway. We started with airspeed measurements, and somehow you were bringing special relativity into it.
Could you please elaborate on that part of converation?
Just to remind you:
patrickjp93 wrote:
mwananchi wrote:
patrickjp93 wrote:
And you don't need the AoA to get your air speed. Using triangulation from the radar sensors or Boeing's upcoming Lidar implementation, you can derive craft speed based on the bounce time of reflected beams at a given distance ahead since Special Relativity is a well-understood scheme at this point.

Take the case of over-water flights: whether radar would provide actual craft speed readings is probably a question for the forum experts to chew over.

Lidar at high altitude over water for speed measurement purposes sounds like quite an advanced application too.

Special relativity doesn't give a damn about being overwater, or did you forget we have overseas satellites. You can use light's deflection off the air and the time it takes to receive the reflection, because the speed of light is constant regardless of its emitter having non-zero speed.

dtw2hyd
Posts: 7469
Joined: Wed Jan 09, 2013 12:11 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

phollingsworth wrote:
dtw2hyd wrote:
The LEAP program started in 2005 and LEAP engines were launched in 2008. Nine years is enough time to realize engines are too big.

Visually for me, C-Series engines looked disproportionately big for the frame, how is it handling CG issues?

The LEAP programme is different from the LEAP-1B which is a specific engine type. Legally it is a different engine from the LEAP-1A/C. The sizing of the LEAP-2 was done in concert with the sizing of the 737MAX.

As for the engine being too big. I am flummoxed by the idea that it is physically too big for the airframe. However, its size and the resulting installation requirements meant that the predictions of aircraft performance approaching stall were less precise than they would otherwise have been. This ultimately necessitated changes to the flight control system to ensure compliance with the certification standards. Changes to the flight control system are not unheard of between variants of aircraft. We saw it with the DC-9 series which stayed on one TC just like the 737.

The issue is that Boeing 'convinced' the regulators that these changes were transparent to the flight crews and the failure modes were sufficiently similar to those for prior 737s that no further training was necessary. Further, Boeing also convinced the regulator that the severity of failure in the new system was sufficiently low that the fail-active situation did not have to be mitigated against. In reality these were not the case. The system is somewhat different in normal operations, such that it might cause confusion when operating as intended, and its failure mode is sufficiently different so as to create catastrophic chains where they did not exist before.

The issue with the performance as the aircraft approaches stall has little to do with the CG changes from the engines being heavier, which is a function of mass distribution about the aircraft, but instead has to do with the location of the neutral point (NP) and the effective aerodynamic centre of the wing (AC), plus the lift curve slope of the wing/nacelle/body configuration approaching and through 'stall'. The stick force is a function of how close the neutral point is to the centre of gravity. The closer they are together the more elevator authority you have. This means you would need less stick force to increase the pitch angle and angle of attack. The distance between the NP and CG is known as static margin. In the first order we teach people that the AC of a wing and the resulting NP of an aircraft don't change with AoA. However, that isn't true. The AC and NP only remain fixed a few situations, and in reality we don't want it to remain fixed (for the purposes of stall ID). For Aft-swept wing aircraft the NP moves forward as the Angle of attack increases. This will reduce stick forces. When coupled with a closely coupled nacelle it will more even more radically forward, hence the need to 'artificially' increase stick force by moving the aircraft out of trim. Note you get a similar issue with increasing Mach where the neutral point moves aft as Mach increases. The result is that as you slow down, and your angle of attack increases you can get stick lightening also, hence one of the reasons for Mach trim on deceleration.

Another problem with the aerodynamics that cause the NP to move is that they also reduce the ability of the aircraft to stall 'cleanly'. Ideally, you would like the wing to stall in such a way that the stick force required to maintain AoA is effectively infinite. This prevents the pilot from holding the aircraft in a stall or worse 'deepening' the stall. This problem was identified with a number of non-FBW aircraft, including the 737NG by the European airworthiness authorities. It looks as if MAX's stall performance is even less defined hence the 1g MCAS rules. While T-tail aircraft are know to have "deep stall" problems, whereby you cannot bring the nose down from some stall conditions, this problem isn't universal. 727s don't exhibit true deep stall, and it looks like the longer bodied DC-9 series doesn't either. However, both airframes have issues with stall identification, which has lead to a couple of fatal accidents where pilots held the aircraft in a stall. The A330 and A320 without envelope protection also exhibit this problem.

The solution to the stall identification problem is relatively straight-forward. You add some form of angle of attack envelope protection. This can be 'soft' or 'hard'. The softest form is to modify the elevator feel, either by nudging the stick slightly or miss-trimming the aircraft as you approach stall. This is what the Speed trim system in 737NG does. The harder methods include a stick pusher/kicker which physically forces the stick forward (making it increasingly hard to hold back) to not allowing the aircraft to be above a given angle of attack. The problem with this protection is what happens when the sensors that drive it go wrong. The softer the protection the easier it is for the pilot to counter it. If it is soft enough you don't have to ensure that the system is fail-safe. For hard protection systems fail-safe is essential. MCAS is agressive enough and the failure mode different enough from STS that fail-safe was necessary, but not included.

That seems to be a very information post, but I don't want even pretend to understand any of it. Obviously aerodynamics is a complex subject.

Still have few layman questions.

If LEAP was custom built for MAX, why didn't both Boeing/CFM predict potential size/mounting issues?
Is there any relationship between climb rate and AoA. I thought steep climb is high AoA, apparently not.
Read somewhere stall can happen at any speed, height... Why? Also how does a plane in full stall look from outside? The only video I could find is of National 747 cargo plane at Baghram.

Revelation
Posts: 22237
Joined: Wed Feb 09, 2005 9:37 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

patrickjp93 wrote:
Revelation wrote:
patrickjp93 wrote:
When I said you could use a telescoping gear to fix the MAX with the improvements I mentioned, that was a theoretical, clean implementation of telescoping tech. Yes, you'd have to make it active. No, flipping, duh. I never said you could use the MAX 10's gear. I said you could tweak the idea. Now that I've clarified, what do you think? A flipping active landing gear would take less than a month to design, blueprint, 3D print, and test now that we have 3D printers capable of working with and tempering molten metal. The paperwork for safety criticality certification would take longer to do.

FWIW I was responding to a tangential thread about how MAX10 worked not how your idea works. With regard to your idea, I doubt the 1 month estimate is valid. Boeing has access to all that tech and more and it took them much longer to work out the (passive) MAX10 solution. The paperwork isn't just paperwork, it's doing a lot of testing to produce data that is needed to complete the paperwork. As others have indicated, there are boatloads of use cases to consider. Waving your hands and saying they don't matter is how we got MCAS.

No they don't. Boeing and Airbus both are a long ways behind the leading edge of manufacturing tech. GE you could maybe argue for, but not Boeing. Easily 15 years behind.

Boeing (and Airbus too?) being mired with 2005 manufacturing technology seems to be incredulous, especially in the context of Boeing developing a solution to such an important issue as the 737 being reconfigured to avoid the MCAS problem by adapting a more "natural" engine mounting point, but I'll defer to the various industry practitioners on this thread for their input.
Wake up to find out that you are the eyes of the world
The heart has its beaches, its homeland and thoughts of its own
Wake now, discover that you are the song that the morning brings
The heart has its seasons, its evenings and songs of its own

DenverTed
Posts: 385
Joined: Wed Mar 27, 2019 11:12 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

dtw2hyd wrote:
phollingsworth wrote:
dtw2hyd wrote:
The softest form is to modify the elevator feel, either by nudging the stick slightly or miss-trimming the aircraft as you approach stall. This is what the Speed trim system in 737NG does.

I thought that speed trim was cruise control to trim to constant speed? I had not heard that it was some kind of stall or pre stall avoidance.

seahawk
Posts: 9052
Joined: Fri May 27, 2005 1:29 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

patrickjp93 wrote:
Carlitos471 wrote:
seahawk wrote:
It is long due to discuss the role over regulation had in the process. Boeing could have made a better product without FAA oversight.

The FAA didn't prevent Boeing from doing a clean sheet or to design the MAX properly.
Boeing chose not to do it properly. They knew the regulations before they started the development, regulations did't change half way thru.

They did not prevent a clean sheet, but they were directly an impediment to "designing the MAX properly" as I've discussed upthread. If grandfathering frameworks were more flexible in iterative improvement Boeing would have just raised the landing gear and not spend \$300 million USD on building MCAS v1.0 and risked this nightmare.

Exactly. Random "rules" limit the design of the plane. If they would not be sol hell bent on enforcing linear stick control, no MCAS would be needed. If they would allow no slides with a higher landing gear, the engine could be mounted differently.

rheinwaldner
Posts: 1845
Joined: Wed Jan 02, 2008 4:58 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

patrickjp93 wrote:
When I said you could use a telescoping gear to fix the MAX with the improvements I mentioned, that was a theoretical, clean implementation of telescoping tech. Yes, you'd have to make it active. No, flipping, duh. I never said you could use the MAX 10's gear. I said you could tweak the idea. Now that I've clarified, what do you think? A flipping active landing gear would take less than a month to design, blueprint, 3D print, and test now that we have 3D printers capable of working with and tempering molten metal. The paperwork for safety criticality certification would take longer to do.

How naive are you? The "one month" is just your pipe dream. And - it does not contain the work to integrate the engine differently on the wing. Which means basically doing the entire MAX project scope once more. Which means EIS in 2022-2024. And, it would probably require to scrap all the existing MAXs.

patrickjp93 wrote:
You can claim to have a PhD, but that doesn't matter to me. Let's see you prove the argument rather than rest on your laurels.

At least Kalvados argument turned down your utterly ridiculous idea of the special relativity speed measurement.

I am an engineer and I would consider people like you to be dangerous in any project, because you argue with arrogance, are unwilling to comply with constraints, are underestimating efforts by a long shot and are misjudging interdisciplinary questions.
Many things are difficult, all things are possible!

rheinwaldner
Posts: 1845
Joined: Wed Jan 02, 2008 4:58 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

seahawk wrote:
Exactly. Random "rules" limit the design of the plane. If they would not be sol hell bent on enforcing linear stick control, no MCAS would be needed. If they would allow no slides with a higher landing gear, the engine could be mounted differently.

Yes, anyway evacuating at cruise level would also solve the MCAS problem. If only these bad rules would not prevent that.
Many things are difficult, all things are possible!

scbriml
Posts: 18094
Joined: Wed Jul 02, 2003 10:37 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

patrickjp93 wrote:
I'm really not sure at this point how to make my posts more crystal clear, but here goes.

Obviously you weren’t crystal clear to begin with. You started talking incorrectly about the MAX 10 gear and segued into some fantasy gear that fixes all the MAX issues in a month. Aside from the fact Boeing, with all their resources didn’t take your route, I wasn’t the only one confused by your postings.
Time flies like an arrow. Fruit flies like a banana!
There are 10 types of people in the World - those that understand binary and those that don't.

seahawk
Posts: 9052
Joined: Fri May 27, 2005 1:29 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

rheinwaldner wrote:
seahawk wrote:
Exactly. Random "rules" limit the design of the plane. If they would not be sol hell bent on enforcing linear stick control, no MCAS would be needed. If they would allow no slides with a higher landing gear, the engine could be mounted differently.

Yes, anyway evacuating at cruise level would also solve the MCAS problem. If only these bad rules would not prevent that.

If the crew were correctly trained in the use of the passenger parachutes, yes.

FluidFlow
Posts: 465
Joined: Wed Apr 10, 2019 6:39 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

morrisond wrote:
FluidFlow wrote:
patrickjp93 wrote:
We need to add it to the list of things to address to fix problems across the industry. I gave a perfectly reasonable explanation of what is wrong with the rigid framework of grandfathering. It was more expensive to develop MCAS and move the engines forward than it would have been to raise the landing gear, but raising the gear was made off-limits under grandfathering for the type. That's a failure of the regulation framework, simple as that. Iterative improvement has to be allowed.

Besides the rules: Boeing was not able to just raise the ground clearance because it would have changed the wing and fuselage a lot: taller gear means bigger bay, means changes to the wing and fuselage. Also the front gear would have needed an extension and triggered changes at the fuselage there.

It was not only the slides that would have had to be installed, the wing and probably the wing box would have need redesign due to changes needed to accommodate the taller landing gear. So the regulations are just an excuse here.

I believe the 777X got a new wing box and gear - no idea if it's higher clearance though.

https://www.flightglobal.com/systems-an ... 38.article

Exactly and they still could grandfather the rest of the frame. But for the 737 Boeing decided to also grandfather the wing + gear etc. so they could not change it. It was their decision that limited the ground clearance. If they had made the decision to raise ground clearance change the box and add slides, the problem would not be there. But that would have cost another \$1B+ in R&D and Boeing decided against it.

Posts: 2263
Joined: Wed Mar 01, 2006 4:29 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

FluidFlow wrote:
morrisond wrote:
FluidFlow wrote:

Besides the rules: Boeing was not able to just raise the ground clearance because it would have changed the wing and fuselage a lot: taller gear means bigger bay, means changes to the wing and fuselage. Also the front gear would have needed an extension and triggered changes at the fuselage there.

It was not only the slides that would have had to be installed, the wing and probably the wing box would have need redesign due to changes needed to accommodate the taller landing gear. So the regulations are just an excuse here.

I believe the 777X got a new wing box and gear - no idea if it's higher clearance though.

https://www.flightglobal.com/systems-an ... 38.article

Exactly and they still could grandfather the rest of the frame. But for the 737 Boeing decided to also grandfather the wing + gear etc. so they could not change it. It was their decision that limited the ground clearance. If they had made the decision to raise ground clearance change the box and add slides, the problem would not be there. But that would have cost another \$1B+ in R&D and Boeing decided against it.

\$1B is a very conservative estimate for a clean sheet design

phollingsworth
Posts: 743
Joined: Sat Mar 06, 2004 6:05 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

DenverTed wrote:
dtw2hyd wrote:
phollingsworth wrote:

I thought that speed trim was cruise control to trim to constant speed? I had not heard that it was some kind of stall or pre stall avoidance.

The original Speed/Mach trim function was created to account for the shift in neutral point as the Mach number increases and decreases, e.g. avoid Mach Tuck (which can kill you). However, over the years is have been expanded to provide a number of additional functions, primarily around speed stability. This is critical at low speed, high AoA where if the aircraft gets behind the power curve and is negatively stable in speed you can rapidly approach stall. STS does this by actively trimming the aircraft to a higher speed than it is currently flying at (eg more nose down). When the 737NG was certified in the mid 1990s the FAA was fine with the handling and stall ID characteristics of the aircraft. However, the JAA baulked at it. The JAA, mainly from the legacy of the UK CAA is very stall averse. As such they required an augmentation system to help identify stall (different than avoidance). This is because the 737 does not have hard envelope limits. Since the NGs behaviour around stall only needs the pilot to let go of the yoke, Boeing got away without using a stick pusher. Instead they made STS even more aggressive as Vs is approached, making it even harder to hold AoA. This effectively makes the aircraft behave like it has a clean stall before it even stalls. Boeing even did a press release about this in 1997. Because of the history of the 737 the STS uses only one Pitot-Static system at a time (I believe there are two computers that can be switched between). Therefore if the pitot-static system fails to a low speed the system will runaway nose down. Boeing use the now infamous 'bad maths' to show that this STS was ok. It turns out that it probably is, even if the pilots are less likely to diagnose it properly and quick as the failure rate of the system is much lower than the original estimates.

phollingsworth
Posts: 743
Joined: Sat Mar 06, 2004 6:05 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

dtw2hyd wrote:
phollingsworth wrote:
dtw2hyd wrote:
The LEAP program started in 2005 and LEAP engines were launched in 2008. Nine years is enough time to realize engines are too big.

Visually for me, C-Series engines looked disproportionately big for the frame, how is it handling CG issues?

The LEAP programme is different from the LEAP-1B which is a specific engine type. Legally it is a different engine from the LEAP-1A/C. The sizing of the LEAP-2 was done in concert with the sizing of the 737MAX.

As for the engine being too big. I am flummoxed by the idea that it is physically too big for the airframe. However, its size and the resulting installation requirements meant that the predictions of aircraft performance approaching stall were less precise than they would otherwise have been. This ultimately necessitated changes to the flight control system to ensure compliance with the certification standards. Changes to the flight control system are not unheard of between variants of aircraft. We saw it with the DC-9 series which stayed on one TC just like the 737.

The issue is that Boeing 'convinced' the regulators that these changes were transparent to the flight crews and the failure modes were sufficiently similar to those for prior 737s that no further training was necessary. Further, Boeing also convinced the regulator that the severity of failure in the new system was sufficiently low that the fail-active situation did not have to be mitigated against. In reality these were not the case. The system is somewhat different in normal operations, such that it might cause confusion when operating as intended, and its failure mode is sufficiently different so as to create catastrophic chains where they did not exist before.

The issue with the performance as the aircraft approaches stall has little to do with the CG changes from the engines being heavier, which is a function of mass distribution about the aircraft, but instead has to do with the location of the neutral point (NP) and the effective aerodynamic centre of the wing (AC), plus the lift curve slope of the wing/nacelle/body configuration approaching and through 'stall'. The stick force is a function of how close the neutral point is to the centre of gravity. The closer they are together the more elevator authority you have. This means you would need less stick force to increase the pitch angle and angle of attack. The distance between the NP and CG is known as static margin. In the first order we teach people that the AC of a wing and the resulting NP of an aircraft don't change with AoA. However, that isn't true. The AC and NP only remain fixed a few situations, and in reality we don't want it to remain fixed (for the purposes of stall ID). For Aft-swept wing aircraft the NP moves forward as the Angle of attack increases. This will reduce stick forces. When coupled with a closely coupled nacelle it will more even more radically forward, hence the need to 'artificially' increase stick force by moving the aircraft out of trim. Note you get a similar issue with increasing Mach where the neutral point moves aft as Mach increases. The result is that as you slow down, and your angle of attack increases you can get stick lightening also, hence one of the reasons for Mach trim on deceleration.

Another problem with the aerodynamics that cause the NP to move is that they also reduce the ability of the aircraft to stall 'cleanly'. Ideally, you would like the wing to stall in such a way that the stick force required to maintain AoA is effectively infinite. This prevents the pilot from holding the aircraft in a stall or worse 'deepening' the stall. This problem was identified with a number of non-FBW aircraft, including the 737NG by the European airworthiness authorities. It looks as if MAX's stall performance is even less defined hence the 1g MCAS rules. While T-tail aircraft are know to have "deep stall" problems, whereby you cannot bring the nose down from some stall conditions, this problem isn't universal. 727s don't exhibit true deep stall, and it looks like the longer bodied DC-9 series doesn't either. However, both airframes have issues with stall identification, which has lead to a couple of fatal accidents where pilots held the aircraft in a stall. The A330 and A320 without envelope protection also exhibit this problem.

The solution to the stall identification problem is relatively straight-forward. You add some form of angle of attack envelope protection. This can be 'soft' or 'hard'. The softest form is to modify the elevator feel, either by nudging the stick slightly or miss-trimming the aircraft as you approach stall. This is what the Speed trim system in 737NG does. The harder methods include a stick pusher/kicker which physically forces the stick forward (making it increasingly hard to hold back) to not allowing the aircraft to be above a given angle of attack. The problem with this protection is what happens when the sensors that drive it go wrong. The softer the protection the easier it is for the pilot to counter it. If it is soft enough you don't have to ensure that the system is fail-safe. For hard protection systems fail-safe is essential. MCAS is agressive enough and the failure mode different enough from STS that fail-safe was necessary, but not included.

That seems to be a very information post, but I don't want even pretend to understand any of it. Obviously aerodynamics is a complex subject.

Still have few layman questions.

If LEAP was custom built for MAX, why didn't both Boeing/CFM predict potential size/mounting issues?
Is there any relationship between climb rate and AoA. I thought steep climb is high AoA, apparently not.
Read somewhere stall can happen at any speed, height... Why? Also how does a plane in full stall look from outside? The only video I could find is of National 747 cargo plane at Baghram.

Let's see if I can answer your questions in appropriate layman's terms (my challenge).
• Boeing, with CFM, will have spent a lot of time deciding on the 'best' configuration for them in terms of fan diameter, placement and the like. From what I have seen it looks like the exact positioning of the engines on the wing wasn't fully dictated by clearance as the -10 moves the engines back a slight amount (I don't know if this is true). This means that factors like aerodynamic efficiency would have played a role in the choice. Unfortunately, engineering design is always a bit of a gamble as the predictions will not always come true. Especially in the areas of interaction between different components of the aircraft, e.g. wing-nacelle. As such some of the non-linear behaviour won't show up until you do physical testing. This looks to be the case for the MAX. As they say 'you pay your money, you take your chances'.
• Yes, but probably not in the way you are thinking. Maximum rate-of-climb and maximum climb angle will occur at a single AoA for each case. For maximum rate this is the AoA that gives the maximum lift-to-drag ratio. This will not be a high AoA, but might be a high pitch angle. This is confusing for many people. Pitch angle is the aircraft relative to the horizon, AoA is the angle relative to the local wind. So an aircraft can have a pitch angle of 20° but an AoA of only 2°.
• Stall is, in the first order, a function of AoA, as such it can happen at any speed and altitude. I have stalled an aircraft in a 4g turn, and in a -1.5g turn. Speed, via Reynold's and Mach numbers, does effect the AoA of stall, but those are second order effects. As to what an aircraft looks like in a stall. That really depends, some are very heavily nose-up, e.g. Baghram. However, others would look almost flat. AF447 had and AoA of ~35°, well past the stall point, but given the rate of descent it would have been almost level in pitch through most of the accident progression.

Don't worry about having trouble with these concepts, we have Aerospace Engineering academics that can't properly describe the conditions, especially how they look on a built-up aircraft.

PepeTheFrog
Posts: 96
Joined: Mon Dec 16, 2019 10:38 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

According to this guy at Leeham restarting production and getting up to speed again will take years:

https://leehamnews.com/2020/01/15/boein ... suppliers/

The MAX fiasco puts Boeing so much behind Airbus in the narrowbody race, I wonder if Boeing will ever catch up?

phollingsworth
Posts: 743
Joined: Sat Mar 06, 2004 6:05 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

asdf wrote:
phollingsworth wrote:
asdf wrote:

so unbelivable ...
what are you guys writing of here?

one never ever needed augmentation of stickforce in any manual controlled airplane before the clown&monkey 737MAX

Except the A300/A310. Peter Lemming presented a whole blog post on that system.

thank you

Sorry, misspelled Peter's name. It is Peter Lemme. He has a blog at satcom.guru and is @satcomguru on Twitter. The discussion if the A300/A310 is in the twitter feed, but there are a lot of very worthwhile discussions on his blog that relate.

I am having trouble searching Twitter right now, but I think this is the correct thread:

PixelFlight
Posts: 958
Joined: Thu Nov 08, 2018 11:09 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

phollingsworth wrote:
DenverTed wrote:
dtw2hyd wrote:

I thought that speed trim was cruise control to trim to constant speed? I had not heard that it was some kind of stall or pre stall avoidance.

The original Speed/Mach trim function was created to account for the shift in neutral point as the Mach number increases and decreases, e.g. avoid Mach Tuck (which can kill you). However, over the years is have been expanded to provide a number of additional functions, primarily around speed stability. This is critical at low speed, high AoA where if the aircraft gets behind the power curve and is negatively stable in speed you can rapidly approach stall. STS does this by actively trimming the aircraft to a higher speed than it is currently flying at (eg more nose down). When the 737NG was certified in the mid 1990s the FAA was fine with the handling and stall ID characteristics of the aircraft. However, the JAA baulked at it. The JAA, mainly from the legacy of the UK CAA is very stall averse. As such they required an augmentation system to help identify stall (different than avoidance). This is because the 737 does not have hard envelope limits. Since the NGs behaviour around stall only needs the pilot to let go of the yoke, Boeing got away without using a stick pusher. Instead they made STS even more aggressive as Vs is approached, making it even harder to hold AoA. This effectively makes the aircraft behave like it has a clean stall before it even stalls. Boeing even did a press release about this in 1997. Because of the history of the 737 the STS uses only one Pitot-Static system at a time (I believe there are two computers that can be switched between). Therefore if the pitot-static system fails to a low speed the system will runaway nose down. Boeing use the now infamous 'bad maths' to show that this STS was ok. It turns out that it probably is, even if the pilots are less likely to diagnose it properly and quick as the failure rate of the system is much lower than the original estimates.

Interesting, thanks for the explanations.
So it look like the wrong assumptions that affected the MCAS design was set in place for the STS. I wonder what the motivation at that 737 NG time to not design a reliable and redundant full authority FBW trimable horizontal stabilizer. In the 199x there should know already that this was inevitably the future, and the only way to comply with more and more challenging aerodynamic. The 737 MAX would have been easier to do and a lot safer to fly. The NG STS punched a insignificant hole in safety and the MAX MCAS used this as a pretext to enlarge that hole in safety far too much.

phollingsworth
Posts: 743
Joined: Sat Mar 06, 2004 6:05 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

PepeTheFrog wrote:
According to this guy at Leeham restarting production and getting up to speed again will take years:

https://leehamnews.com/2020/01/15/boein ... suppliers/

The MAX fiasco puts Boeing so much behind Airbus in the narrowbody race, I wonder if Boeing will ever catch up?

It all depends on when a legitimate competitor appears, if it happens in the nearer term there is a reasonable likelihood that Boeing will exit the commercial aircraft business in the next 10 years. If it take longer then Boeing has a chance to recover. Airbus will benefit to a small extent; however, in reality the airlines will suffer.

phollingsworth
Posts: 743
Joined: Sat Mar 06, 2004 6:05 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

PixelFlight wrote:
phollingsworth wrote:
DenverTed wrote:
I thought that speed trim was cruise control to trim to constant speed? I had not heard that it was some kind of stall or pre stall avoidance.

The original Speed/Mach trim function was created to account for the shift in neutral point as the Mach number increases and decreases, e.g. avoid Mach Tuck (which can kill you). However, over the years is have been expanded to provide a number of additional functions, primarily around speed stability. This is critical at low speed, high AoA where if the aircraft gets behind the power curve and is negatively stable in speed you can rapidly approach stall. STS does this by actively trimming the aircraft to a higher speed than it is currently flying at (eg more nose down). When the 737NG was certified in the mid 1990s the FAA was fine with the handling and stall ID characteristics of the aircraft. However, the JAA baulked at it. The JAA, mainly from the legacy of the UK CAA is very stall averse. As such they required an augmentation system to help identify stall (different than avoidance). This is because the 737 does not have hard envelope limits. Since the NGs behaviour around stall only needs the pilot to let go of the yoke, Boeing got away without using a stick pusher. Instead they made STS even more aggressive as Vs is approached, making it even harder to hold AoA. This effectively makes the aircraft behave like it has a clean stall before it even stalls. Boeing even did a press release about this in 1997. Because of the history of the 737 the STS uses only one Pitot-Static system at a time (I believe there are two computers that can be switched between). Therefore if the pitot-static system fails to a low speed the system will runaway nose down. Boeing use the now infamous 'bad maths' to show that this STS was ok. It turns out that it probably is, even if the pilots are less likely to diagnose it properly and quick as the failure rate of the system is much lower than the original estimates.

Interesting, thanks for the explanations.
So it look like the wrong assumptions that affected the MCAS design was set in place for the STS. I wonder what the motivation at that 737 NG time to not design a reliable and redundant full authority FBW trimable horizontal stabilizer. In the 199x there should know already that this was inevitably the future, and the only way to comply with more and more challenging aerodynamic. The 737 MAX would have been easier to do and a lot safer to fly. The NG STS punched a insignificant hole in safety and the MAX MCAS used this as a pretext to enlarge that hole in safety far too much.

Nothing about the system says 'you must go FBW'. What Boeing should have done, way back when, was to redo the avionics subsystem in the 737 to provide a more unified system. Even bringing it in line with what 757/767 had would have made life much easier. This would have made adopting duplex sensing system to STS and MCAS much easier. In fact the 757 has a sophisticated STS that uses multiple speed sensors and 767-2C and A300/A310 have AoA based pitch augmentation systems similar to MCAS using multiple sensors (767 is duplex, A300/310 is triplex, but only needs duplex for dispatch). The fact is that the computers on the current 737MAX are more than capable of doing the work required. What doesn't exist is a unified architecture to move the information around. This was driven by MTC programmes and not certification and design considerations.

scbriml
Posts: 18094
Joined: Wed Jul 02, 2003 10:37 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

PepeTheFrog wrote:
According to this guy at Leeham restarting production and getting up to speed again will take years:

https://leehamnews.com/2020/01/15/boein ... suppliers/

The MAX fiasco puts Boeing so much behind Airbus in the narrowbody race, I wonder if Boeing will ever catch up?

It will be somewhat discredited because "Leeham's always negative about Boeing", but to be honest, most of what he's saying is just common sense. Some posters here are overly optimistic on how long they think it will take Boeing to ramp production back up and get to the 57 they were aiming for last year, plus deliver 400 stored frames.

When Boeing were still expecting RTS towards the end of 2019, Muilenburg said delivery of stored frames would run into 2021 (without specifying numbers), but that was before they suspended production and said they would prioritise delivering stored frames over new production. But, with the FAA saying they will certify each stored MAX individually, delivery of those frames will drag on for quite a while.

It also seems more than reasonable that starting up production from stop will need to be a gradual build up. It's impossible to go from zero to 42 (let alone return to 52 or increase to 57) MAX a month instantly.

January 29th looks like it will be a pretty painful day for Boeing.
Time flies like an arrow. Fruit flies like a banana!
There are 10 types of people in the World - those that understand binary and those that don't.

dtw2hyd
Posts: 7469
Joined: Wed Jan 09, 2013 12:11 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

phollingsworth wrote:
Let's see if I can answer your questions in appropriate layman's terms (my challenge)....
...
Don't worry about having trouble with these concepts, we have Aerospace Engineering academics that can't properly describe the conditions, especially how they look on a built-up aircraft.

Thank you for the explanation, very informative.

phollingsworth
Posts: 743
Joined: Sat Mar 06, 2004 6:05 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

scbriml wrote:
PepeTheFrog wrote:
According to this guy at Leeham restarting production and getting up to speed again will take years:

https://leehamnews.com/2020/01/15/boein ... suppliers/

The MAX fiasco puts Boeing so much behind Airbus in the narrowbody race, I wonder if Boeing will ever catch up?

...
When Boeing were still expecting RTS towards the end of 2019, Muilenburg said delivery of stored frames would run into 2021 (without specifying numbers), but that was before they suspended production and said they would prioritise delivering stored frames over new production. But, with the FAA saying they will certify each stored MAX individually, delivery of those frames will drag on for quite a while.

It also seems more than reasonable that starting up production from stop will need to be a gradual build up. It's impossible to go from zero to 42 (let alone return to 52 or increase to 57) MAX a month instantly.

January 29th looks like it will be a pretty painful day for Boeing.

The delivery of the stored frames was always going to be a pain. There are just so many of them. When there was a faint hope in quick RTS this was probably manageable in a reasonable timeframe while delivering new frames as they are built. The greater the modifications, especially hardware and the larger the number the harder this becomes. Boeing could commit small number of resources to modifying the stored airframes, but this would run deliveries out for 5 years. By stopping production Boeing can move resources to keeping the delivery of stored aircraft to a reasonable timeframe, at the expense of new builds.

Keep in mind that the FAA has always individually certified aircraft that are built prior to issuance of the TC and the initial airframes built after the TC is issued but not yet included on the PC. The two things that can be implied by the FAA's statements regarding this are:
• They feel the review of certification is significant enough so as to say the 737-8/9Ms are not being built to an existing TC on Boeing's PC.
• The FAA may intend to do conformity themselves instead of letting delegates undertake this conformity

I am very confident in the former and, at least at the start, it is reasonable to assume the latter. There is also the question of how long Boeing thinks it will take to get the TC revision on their PC. You just can't individually conform 40+ aircraft a month, plus do the backlog.

patrickjp93
Posts: 648
Joined: Thu Aug 22, 2019 12:00 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

FluidFlow wrote:
morrisond wrote:
FluidFlow wrote:

Besides the rules: Boeing was not able to just raise the ground clearance because it would have changed the wing and fuselage a lot: taller gear means bigger bay, means changes to the wing and fuselage. Also the front gear would have needed an extension and triggered changes at the fuselage there.

It was not only the slides that would have had to be installed, the wing and probably the wing box would have need redesign due to changes needed to accommodate the taller landing gear. So the regulations are just an excuse here.

I believe the 777X got a new wing box and gear - no idea if it's higher clearance though.

https://www.flightglobal.com/systems-an ... 38.article

Exactly and they still could grandfather the rest of the frame. But for the 737 Boeing decided to also grandfather the wing + gear etc. so they could not change it. It was their decision that limited the ground clearance. If they had made the decision to raise ground clearance change the box and add slides, the problem would not be there. But that would have cost another \$1B+ in R&D and Boeing decided against it.

That's not correct. The 737 is a unique beast in that it's the only craft flying today that is at the 6' off the ground grandfathering limit for not requiring over-wing exit slides as well as cargo loading equipment while also having grandfathered cabling designs for the landing gear and control surfaces. If you change the avionics architecture beyond a cosmetic degree, you break grandfathering and risk requiring an all-new type rating. If Boeing broke its 6' height limit, slides or not, it also broke the type rating. Both outcomes are completely unacceptable and yet were forced on it by the FAA. Boeing screwed up, and so did the FAA.

patrickjp93
Posts: 648
Joined: Thu Aug 22, 2019 12:00 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

patrickjp93 wrote:
You never mentioned clear air turbulence before. Turbulence is irrelevant to the converation anyway. We started with airspeed measurements, and somehow you were bringing special relativity into it.
Could you please elaborate on that part of converation?
Just to remind you:

I didn't mention it before because it's not relevant other than to prove the physics of SR are being used for a different application in the same environment to detect even more minute/precise changes in the air. The only reason I'm bringing it up now is someone with a Physics PhD (which is also irrelevant. Plenty of areas of study other than light, such as Quantum Mechanics, Semiconductor research, fluid dynamics, etc.) is puffing out his/her chest and spouting nonsense.

OK, i guess time to ask... do you know how lidar works?

That would depend upon the use case, because it works in multiple ways. Just as you can use bouncing light beams and changes thereof in a static environment to detect objects moving through the environment, you can then extrapolate the degree of those changes per unit time to gain other information, such as your craft speed in this case, or in the much more minute case, still-air turbulence at incredible distances. At the end of the day it's still building information from the precise capture of deformations of reflected light waves.

Posts: 2263
Joined: Wed Mar 01, 2006 4:29 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

patrickjp93 wrote:
patrickjp93 wrote:
I didn't mention it before because it's not relevant other than to prove the physics of SR are being used for a different application in the same environment to detect even more minute/precise changes in the air. The only reason I'm bringing it up now is someone with a Physics PhD (which is also irrelevant. Plenty of areas of study other than light, such as Quantum Mechanics, Semiconductor research, fluid dynamics, etc.) is puffing out his/her chest and spouting nonsense.

OK, i guess time to ask... do you know how lidar works?

That would depend upon the use case, because it works in multiple ways. Just as you can use bouncing light beams and changes thereof in a static environment to detect objects moving through the environment, you can then extrapolate the degree of those changes per unit time to gain other information, such as your craft speed in this case, or in the much more minute case, still-air turbulence at incredible distances. At the end of the day it's still building information from the precise capture of deformations of reflected light waves.

Nope. Correct answer: time of flight.

keesje
Posts: 13462
Joined: Thu Apr 12, 2001 2:08 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

I think Boeing will be happy if they can deliver 2000 MAX in the next 5-6 years and convert the rest to something better. https://leehamnews.com/2019/11/28/conve ... o-the-fsa/
"Never mistake motion for action." Ernest Hemingway

FluidFlow
Posts: 465
Joined: Wed Apr 10, 2019 6:39 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

patrickjp93 wrote:
FluidFlow wrote:
morrisond wrote:

I believe the 777X got a new wing box and gear - no idea if it's higher clearance though.

https://www.flightglobal.com/systems-an ... 38.article

Exactly and they still could grandfather the rest of the frame. But for the 737 Boeing decided to also grandfather the wing + gear etc. so they could not change it. It was their decision that limited the ground clearance. If they had made the decision to raise ground clearance change the box and add slides, the problem would not be there. But that would have cost another \$1B+ in R&D and Boeing decided against it.

That's not correct. The 737 is a unique beast in that it's the only craft flying today that is at the 6' off the ground grandfathering limit for not requiring over-wing exit slides as well as cargo loading equipment while also having grandfathered cabling designs for the landing gear and control surfaces. If you change the avionics architecture beyond a cosmetic degree, you break grandfathering and risk requiring an all-new type rating. If Boeing broke its 6' height limit, slides or not, it also broke the type rating. Both outcomes are completely unacceptable and yet were forced on it by the FAA. Boeing screwed up, and so did the FAA.

Are you sure and can you support your opinion?

When Boeing went from the classic to the NG a completely new wing was installed and they still could keep the type rating because the avionics stayed the same (with STS). So changing the wing again to have more space for taller gear but keeping the avionics is not a problem under grandfathering the type rating as long as slides are installed and as you stated the loading equipment.

The problem is then not for the pilots rating but a) the aircraft becomes heavier and b) ground handling will have to change for the MAX over the NG. The longer gear will not affect handling of the aircraft from the pilots view as long as it actually does fly the same way. Other changes will have to be made.

And clearly the 6' rule is crap anyway and only exists because of the 737 and is in my opinion a farce as it should be max 3' and all above should need a slide. Not every person is fit to jump off the wing or how ever you get off and I personally would kick people off the wing to get away from the 737 in an emergency if they hesitate to jump and block the way. And I think and am pretty sure scenes like this would happen and god forbid if it does I wanna hear the explanation from the FAA and Boeing if a video shows up with such content and people get hurt.

SomebodyInTLS
Posts: 1802
Joined: Wed Jun 15, 2016 12:31 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

patrickjp93 wrote:
raising the gear was made off-limits under grandfathering for the type.

That's reaaaaaalllly not how grandfathering works.

That's a failure of the regulation framework, simple as that. Iterative improvement has to be allowed.

Grandfathering is simply an option for the manufacturer to SAVE TIME AND MONEY by not re-certifying parts already in use in existing aircraft. You can pick and choose which parts of the aircraft to certify anew and which retain the old, proven, designs - it's not like the 737 must, by definition, have a short landing gear or the whole thing will be re-certified.

If, in your hypthetical situation, moving the engines and adding MCAS is more expensive than extending the gear then OF COURSE BOEING WOULD CHOOSE TO EXTEND THE GEAR! Not off-limits at all as it's the manufacturer's decision.

Unless you mean that additional certification and design work resulting from extending the gear is more expensive than additional certification and design work resulting from moving the engines and adding MCAS... but that can hardly be described as "off limits"...
Last edited by SomebodyInTLS on Wed Jan 15, 2020 1:26 pm, edited 5 times in total.
"As with most things related to aircraft design, it's all about the trade-offs and much more nuanced than A.net likes to make out."

keesje
Posts: 13462
Joined: Thu Apr 12, 2001 2:08 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

Emergency exit regulation on the 737-800 was what triggered the FAA 20 years back to kill grandfathered certification.

Grandfather rights have finally been killed on both sides of the Atlantic. A new US Federal Aviation Administration rule has replaced the regulation which allowed completely new aircraft models in a well established family, like Boeing's 737 series, for example, to continue to be produced to some of the out-of-date certification standards in force when the first 737 was produced.

https://www.flightglobal.com/faa-rules-kill-grandfather-rights-in-usa-and-europe-/32615.article

A decade later, when the 737 needed to be saved from the NEO, everybody suffered from sudden mass amnesia.

https://www.gettyimages.nl/detail/nieuw ... /119436527

The crashes, MCAS design failure surfaced the way the 737MAX was certified 2011-2017. JATR put their finger on the certification process of changed products. It requires a top-down approach whereby every change is evaluated from an integrated whole aircraft system perspective.. no patching. That's why the grounding is taking a year so far, instead of 2 months.
Last edited by keesje on Wed Jan 15, 2020 1:23 pm, edited 2 times in total.
"Never mistake motion for action." Ernest Hemingway

Exeiowa
Posts: 191
Joined: Fri Jul 06, 2018 4:49 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

The rules may have boxed the manufacturer into an unfortunate spot, but they could have made a decision to remove themselves from that box with a new design preventing all the restrictions to stay within it, but choose not to for commercial reasons not safety ones. so are the rules wrong? Maybe, but which rule is wrong the one where grandfathering was allowed indefinitely or the restriction on how a plane is expected to behave.

Ertro
Posts: 70
Joined: Thu Apr 04, 2019 9:28 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

You all look at this issue from benefit of hindsight that was not available at the time when decisions were made. Even if there would have not been any FAA rules affecting landing gear height it is totally possible that Boeing would not have done anything differently.

It is pretty clear that at that moment when major architectural decisions were made about the landing gear and engine placement nobody saw the problems they are going to run into years later and the need to have anything like MCAS at all. All they were set to do was just an easy and cheap minimum upgrade for a plane that is soon to become obsolete anyway with NSA blowing it out from the water after just a couple of years.

Redesigning landing gear was not seen as an easy upgrade so it was left out. Just hang the engines on the wings and that's it. All done. At that time when decisions were made engineers did not see the the problems they are going to run into later like needing MCAS and all what follows. If they would have forecasted everything we can be sure that they would have started doing something differently in a major way already many many years ago.

par13del
Posts: 9521
Joined: Sun Dec 18, 2005 9:14 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

Revelation wrote:
As I wrote earlier, perhaps this is because the emails from that phase were scrubbed and nothing dubious was found,

Without any additional evidence, I would take this approach, after the first crash the initial investigation pointed to MCAS something which most say they knew nothing about, then the second crash happened and MCAS was again front and center. So, unless Boeing was / has been able to successfully hide all documentation related to MCAS from the FAA, the media, whistle blowers and not have the FAA bow to politicians, EASA and other regulators pressure to get / produce the relevant documents, I would say nothing dubious.

A conspiracy hat may then be used for the June submission of the initial MCAS fix where the FAA decided to introduce the bit flip, was it because they knew that once the error of MCAS was identified it would be a simply fix and they needed something else to add to the mix since this was the first time in decades that we had fatal crashes due to design errors? In all the reference links in the other thread we still have not seen much of anything saying how MCAS 2.0 functioned during the June test, nor any details of how it functioned during the line pilots testing of the modified computers in the simulator. We know they all recovered the a/c but using different methods from the published check list and memory items, however, knowing that MCAS was the culprit that drove the a/c into the ground killing hundreds, one would think that the replacement version would get more rift?

I will admit that what still is missing and related to MCAS is the adjustments made to the authority during the test phase, and even that is not discussed much these days, has the reasons for that been accepted? If the EASA test flights start today or later this month, maybe we will finally get additional details then the flood gates will open on the information superhighway.

morrisond
Posts: 2130
Joined: Thu Jan 07, 2010 12:22 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

scbriml wrote:
PepeTheFrog wrote:
According to this guy at Leeham restarting production and getting up to speed again will take years:

https://leehamnews.com/2020/01/15/boein ... suppliers/

The MAX fiasco puts Boeing so much behind Airbus in the narrowbody race, I wonder if Boeing will ever catch up?

It will be somewhat discredited because "Leeham's always negative about Boeing", but to be honest, most of what he's saying is just common sense. Some posters here are overly optimistic on how long they think it will take Boeing to ramp production back up and get to the 57 they were aiming for last year, plus deliver 400 stored frames.

When Boeing were still expecting RTS towards the end of 2019, Muilenburg said delivery of stored frames would run into 2021 (without specifying numbers), but that was before they suspended production and said they would prioritise delivering stored frames over new production. But, with the FAA saying they will certify each stored MAX individually, delivery of those frames will drag on for quite a while.

It also seems more than reasonable that starting up production from stop will need to be a gradual build up. It's impossible to go from zero to 42 (let alone return to 52 or increase to 57) MAX a month instantly.

January 29th looks like it will be a pretty painful day for Boeing.

On the other hand Boeing has stated that they are going to priortize delivery of the stored frames vs returning to previous production levels.

They do have 12,000 workers to draw upon. They won't need all of those to restart at 20-30 frames per month. They were geared to deliver 57 per month. I'm pretty certain that assuming that they get the Okay for RTS within a few months they can clear out the backlog in a year - it won't extend into 2022. That is a little extreme.

Revelation
Posts: 22237
Joined: Wed Feb 09, 2005 9:37 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

PepeTheFrog wrote:
According to this guy at Leeham restarting production and getting up to speed again will take years:

https://leehamnews.com/2020/01/15/boein ... suppliers/

The MAX fiasco puts Boeing so much behind Airbus in the narrowbody race, I wonder if Boeing will ever catch up?

I think that is setting up a false narrative.

It was not thought that MAX was going to catch up even before the JT crash because the market shifted to favor the competitor's product, especially the A321. It's kind of like the A340 vs the 777. If the market prefers your competitor's product all you can do is try to hit your own profit goals (which 737 seemed to be doing before the crash) while waiting for the next generation of technology to come along and allow you to produce a stronger competitor (like Airbus did with A350).
Wake up to find out that you are the eyes of the world
The heart has its beaches, its homeland and thoughts of its own
Wake now, discover that you are the song that the morning brings
The heart has its seasons, its evenings and songs of its own

Checklist787
Posts: 372
Joined: Sat Jun 01, 2019 2:37 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

scbriml wrote:
PepeTheFrog wrote:
According to this guy at Leeham restarting production and getting up to speed again will take years:

https://leehamnews.com/2020/01/15/boein ... suppliers/

The MAX fiasco puts Boeing so much behind Airbus in the narrowbody race, I wonder if Boeing will ever catch up?

It will be somewhat discredited because "Leeham's always negative about Boeing", but to be honest, most of what he's saying is just common sense. Some posters here are overly optimistic on how long they think it will take Boeing to ramp production back up and get to the 57 they were aiming for last year, plus deliver 400 stored frames.

When Boeing were still expecting RTS towards the end of 2019, Muilenburg said delivery of stored frames would run into 2021 (without specifying numbers), but that was before they suspended production and said they would prioritise delivering stored frames over new production. But, with the FAA saying they will certify each stored MAX individually, delivery of those frames will drag on for quite a while.

It also seems more than reasonable that starting up production from stop will need to be a gradual build up. It's impossible to go from zero to 42 (let alone return to 52 or increase to 57) MAX a month instantly.

January 29th looks like it will be a pretty painful day for Boeing.

You forgot to mention that:

"A new airplane is needed for Boeing to be competitive again. (This was needed before the grounding, by the way.)"

Leehamnews

As I always said,

with or without 737MAX, Boeing will be NOT necessarly to launch a brand new clean cheet design at least around 2022 without necessarily being a 737 replacement.

...

It is very "good for me" , we will talk about it again ...

phollingsworth
Posts: 743
Joined: Sat Mar 06, 2004 6:05 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

par13del wrote:
Revelation wrote:
...
I will admit that what still is missing and related to MCAS is the adjustments made to the authority during the test phase, and even that is not discussed much these days, has the reasons for that been accepted? If the EASA test flights start today or later this month, maybe we will finally get additional details then the flood gates will open on the information superhighway.

Obviously, there isn't the whole chain of the decision making authority. However, the extension and increase rates at 1g would jive with increase stall identification. If you want the aircraft to pitch down rapidly in the pre, at, and post-stall regime you would need much faster stab movement than you would for just keeping stick force in the acceptable level. That would explain the rate change. The question to ask is why is repeated application required in this instance? My guess is that the keep the whole thing simple is the driver. MCAS0.9 had repeated application to avoid fusing multiple sensor readings. It would be more work to set it up without it for the 1g case. A much better design would have been application based on levels of AoA, but a single one for any given AoA reading. This would have removed the new failure mode, but not necessarily fixed the hazard assessment issue.

asdf
Posts: 584
Joined: Tue Mar 18, 2014 12:03 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

phollingsworth wrote:
par13del wrote:
Revelation wrote:
...
I will admit that what still is missing and related to MCAS is the adjustments made to the authority during the test phase, and even that is not discussed much these days, has the reasons for that been accepted? If the EASA test flights start today or later this month, maybe we will finally get additional details then the flood gates will open on the information superhighway.

Obviously, there isn't the whole chain of the decision making authority. However, the extension and increase rates at 1g would jive with increase stall identification. If you want the aircraft to pitch down rapidly in the pre, at, and post-stall regime you would need much faster stab movement than you would for just keeping stick force in the acceptable level. That would explain the rate change. The question to ask is why is repeated application required in this instance? My guess is that the keep the whole thing simple is the driver. MCAS0.9 had repeated application to avoid fusing multiple sensor readings. It would be more work to set it up without it for the 1g case. A much better design would have been application based on levels of AoA, but a single one for any given AoA reading. This would have removed the new failure mode, but not necessarily fixed the hazard assessment issue.

if it would simply be a "stick feeling" thing there had not been a need to change the not certified adjustment of MCAS to 600% from the initial augmentation

if it would simply be a "stick feeling" thing they could find a nice new bing-bang-beng audio alarm and let a se*y automated female voice comment it with "maneuver caution, expect light stick, observe AoA - maneuver caution, expect light stick, observe AoA - maneuver caution, expect light stick, observe AoA" or such

I think it isn't
I think its the flawed aerodynamical attitude of the 737MAX what is the problem

mjoelnir
Posts: 9193
Joined: Sun Feb 03, 2013 11:06 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

Revelation wrote:
PepeTheFrog wrote:
According to this guy at Leeham restarting production and getting up to speed again will take years:

https://leehamnews.com/2020/01/15/boein ... suppliers/

The MAX fiasco puts Boeing so much behind Airbus in the narrowbody race, I wonder if Boeing will ever catch up?

I think that is setting up a false narrative.

It was not thought that MAX was going to catch up even before the JT crash because the market shifted to favor the competitor's product, especially the A321. It's kind of like the A340 vs the 777. If the market prefers your competitor's product all you can do is try to hit your own profit goals (which 737 seemed to be doing before the crash) while waiting for the next generation of technology to come along and allow you to produce a stronger competitor (like Airbus did with A350).

It is actually the right narrative. For a while some posters talked about that not orders counted in the narrow body race, but deliveries. Now deliveries and orders are both down at Boeing. Orders have been negative this year and when deliveries start and than production has to be ramped up, the numbers will be significantly down for Boeing. In this narrow body race, market presens, aka how many frames are flying with the airlines, have also a force all by it's own.

There are about the same number of A320 family frames in use than 737, that will shift significantly now.

phollingsworth
Posts: 743
Joined: Sat Mar 06, 2004 6:05 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

asdf wrote:
phollingsworth wrote:
par13del wrote:

Obviously, there isn't the whole chain of the decision making authority. However, the extension and increase rates at 1g would jive with increase stall identification. If you want the aircraft to pitch down rapidly in the pre, at, and post-stall regime you would need much faster stab movement than you would for just keeping stick force in the acceptable level. That would explain the rate change. The question to ask is why is repeated application required in this instance? My guess is that the keep the whole thing simple is the driver. MCAS0.9 had repeated application to avoid fusing multiple sensor readings. It would be more work to set it up without it for the 1g case. A much better design would have been application based on levels of AoA, but a single one for any given AoA reading. This would have removed the new failure mode, but not necessarily fixed the hazard assessment issue.

if it would simply be a "stick feeling" thing there had not been a need to change the not certified adjustment of MCAS to 600% from the initial augmentation

if it would simply be a "stick feeling" thing they could find a nice new bing-bang-beng audio alarm and let a se*y automated female voice comment it with "maneuver caution, expect light stick, observe AoA - maneuver caution, expect light stick, observe AoA - maneuver caution, expect light stick, observe AoA" or such

I think it isn't
I think its the flawed aerodynamical attitude of the 737MAX what is the problem

The 1g regime will not be stick feel, it will be 'make sure the pilots know you have stalled the aircraft'. EASA will not allow a voice saying you are approaching stall, you have stalled for normal operations. Otherwise a stick shaker would be sufficient. This is not 737MAX issue alone. The fact is that the hard AoA limit on Airbus FBW aircraft are what make them certifiable, without this they fail EASA's stall identification requirement, the 737NG fails without STS. Yes 737MAX has less desirable behaviour than the NG, but that does not automatically make it flawed. Stall identification is a real issue and has lead to several accidents over the years, AF447 just being one example.

Revelation
Posts: 22237
Joined: Wed Feb 09, 2005 9:37 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

par13del wrote:

Revelation wrote:

As I wrote earlier, perhaps this is because the emails from that phase were scrubbed and nothing dubious was found,

Without any additional evidence, I would take this approach, after the first crash the initial investigation pointed to MCAS something which most say they knew nothing about, then the second crash happened and MCAS was again front and center. So, unless Boeing was / has been able to successfully hide all documentation related to MCAS from the FAA, the media, whistle blowers and not have the FAA bow to politicians, EASA and other regulators pressure to get / produce the relevant documents, I would say nothing dubious.

The story reported by ST (repeated below) just seems hard to believe without some overt orchestration by management to curtail the test matrix, which often gets some sort of push back from engineering. Of course I could be wrong and the engineers silently complied, or they just lacked the motivation to dig very deeply at all. I agree that eventually we should find out one way or the other.

The decision to not redo the safety analysis after extending MCAS to the low end of the flight envelope also seems like something that should have left some sort of paper trail. Clearly it involved changing the MCAS software so if nothing else there should be a clear record of which engineer changed the code so you know who to start asking.

Ertro wrote:
Redesigning landing gear was not seen as an easy upgrade so it was left out. Just hang the engines on the wings and that's it. All done. At that time when decisions were made engineers did not see the the problems they are going to run into later like needing MCAS and all what follows. If they would have forecasted everything we can be sure that they would have started doing something differently in a major way already many many years ago.

It's not that they didn't see the problems, it's like they seemingly did not look very hard at all for problems. I personally still think the problems with the engine placement are solvable using an improved MCAS and dual active flight computer configuration, but this is only happening now because Boeing have now been forced by the crashes to step back and sort through all the implications in order to save their investment in MAX, and that of their partners and customers.

With regard to MCAS, in viewtopic.php?f=3&t=1437867&p=21935495&hilit=revelation#p21935495 I wrote the way ST explains it, during the Functional Health Assessment phase Boeing only did the simplest of MCAS use cases, one single activation, then used nothing more formal than an email from minutes of a test pilot's meeting to justify that multiple activation was no worse than single activation. This allowed them to classify MCAS as "major" rather than "hazardous" inside the normal flight envelope, which in turn allowed them to avoid doing a Fault Tree Analysis and a Failure Modes and Effects Analysis for MCAS which may have turned up all the issues with sensor erross and with multiple activations, and allowed use of a single AoA sensor. The dubious math of the "accepted method" was used to then say that the risk outside the normal flight envelope also was not "hazardous" since the odds of being outside the normal flight envelope were low. Then the evaluation was not changed after MCAS was extended to the low speed end of the flight envelope which would have changed the dubious math in an unfavorable way.

It seems like Boeing was following the letter of the law but not its intention. If they had, they would have probably found the MCAS multiple activation problem, but they also probably would have found they needed multiple active sensors too, which would have conflicted with their goal to minimize changes and thus cost. Of course we now know they certainly did not end up minimizing cost due to their poor engineering. The people doing the analysis seemed to be driving with blinders on. They might actually had gotten away with it if someone had done a use case (on paper or in the engineering simulator or in flight) where bad AoA data triggered multiple MCAS activations and used that get the MCAS code cleaned up, but their own decision to minimize cost seems to have prevented them from doing a credible job at systems analysis.
Last edited by Revelation on Wed Jan 15, 2020 3:11 pm, edited 1 time in total.
Wake up to find out that you are the eyes of the world
The heart has its beaches, its homeland and thoughts of its own
Wake now, discover that you are the song that the morning brings
The heart has its seasons, its evenings and songs of its own

Posts: 393
Joined: Sat Oct 26, 2013 2:44 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

John Leahy was prophetic about it all.

Revelation
Posts: 22237
Joined: Wed Feb 09, 2005 9:37 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

John Leahy was prophetic about it all.

Do tell.
Wake up to find out that you are the eyes of the world
The heart has its beaches, its homeland and thoughts of its own
Wake now, discover that you are the song that the morning brings
The heart has its seasons, its evenings and songs of its own

Posts: 2263
Joined: Wed Mar 01, 2006 4:29 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

par13del wrote:
Revelation wrote:
As I wrote earlier, perhaps this is because the emails from that phase were scrubbed and nothing dubious was found,

Without any additional evidence, I would take this approach, after the first crash the initial investigation pointed to MCAS something which most say they knew nothing about, then the second crash happened and MCAS was again front and center. So, unless Boeing was / has been able to successfully hide all documentation related to MCAS from the FAA, the media, whistle blowers and not have the FAA bow to politicians, EASA and other regulators pressure to get / produce the relevant documents, I would say nothing dubious.

A conspiracy hat may then be used for the June submission of the initial MCAS fix where the FAA decided to introduce the bit flip, was it because they knew that once the error of MCAS was identified it would be a simply fix and they needed something else to add to the mix since this was the first time in decades that we had fatal crashes due to design errors? In all the reference links in the other thread we still have not seen much of anything saying how MCAS 2.0 functioned during the June test, nor any details of how it functioned during the line pilots testing of the modified computers in the simulator. We know they all recovered the a/c but using different methods from the published check list and memory items, however, knowing that MCAS was the culprit that drove the a/c into the ground killing hundreds, one would think that the replacement version would get more rift?

I will admit that what still is missing and related to MCAS is the adjustments made to the authority during the test phase, and even that is not discussed much these days, has the reasons for that been accepted? If the EASA test flights start today or later this month, maybe we will finally get additional details then the flood gates will open on the information superhighway.

Well, bit flip is not punitive. Computers demonstrated that a error can be very dnagerous; so this is about bringing computer to the standard required for such high-hazard application. It is about having a FBW-grade computer for the plane which demonstrated worst possible FBW issue - flying into the ground despite pilot's efforts to avoid that. TWICE.
MCAS authority change is a more messy subject, especially how that change was accepted. General narrative - problem which was envisioned only at high speed turned up at lower speed as well, hence all the change. but there should be more to that story.

Jetty
Posts: 1118
Joined: Wed Nov 11, 2015 12:27 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

John Leahy was prophetic about it all.

Definitely not all. He said the the MAX would be the low risk option for Boeing. It turned out to be a very high risk one.

Revelation
Posts: 22237
Joined: Wed Feb 09, 2005 9:37 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

Well, bit flip is not punitive. Computers demonstrated that a error can be very dnagerous; so this is about bringing computer to the standard required for such high-hazard application. It is about having a FBW-grade computer for the plane which demonstrated worst possible FBW issue - flying into the ground despite pilot's efforts to avoid that. TWICE.
MCAS authority change is a more messy subject, especially how that change was accepted. General narrative - problem which was envisioned only at high speed turned up at lower speed as well, hence all the change. but there should be more to that story.

Yes, MCAS 1.0 made it very obvious that the FCC (which used to only host lower hazard tasks such as autopilot) had now become host to hazardous applications. If any sort of sensible analysis of MCAS 1.0 was performed (hmm, what happens when the AoA input is unreliable?) and it was coded to a professional standard we probably would not have discovered that FCC was indeed hosting hazardous applications and needed to be hardened.

I agree that there probably is more to the low speed MCAS change story. The dubious math only worked because the odds of being in the high speed part outside of the normal flight envelope were low. MCAS activation in the low speed range changed that. We still don't know why the implications were not understood.
Wake up to find out that you are the eyes of the world
The heart has its beaches, its homeland and thoughts of its own
Wake now, discover that you are the song that the morning brings
The heart has its seasons, its evenings and songs of its own

WIederling
Posts: 8913
Joined: Sun Sep 13, 2015 2:15 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

dtw2hyd wrote:
Read somewhere stall can happen at any speed, height... Why? Also how does a plane in full stall look from outside? The only video I could find is of National 747 cargo plane at Baghram.

Climb describes your CoG path relative to earth.

In a sane environment increasing AoA increases lift.
If you have reserve lift in climb or any other flight phase your AoA will be benign.
If increasing AoA does not create more lift you are in stall :-=
Murphy is an optimist

DenverTed
Posts: 385
Joined: Wed Mar 27, 2019 11:12 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

phollingsworth wrote:
DenverTed wrote:
dtw2hyd wrote:

I thought that speed trim was cruise control to trim to constant speed? I had not heard that it was some kind of stall or pre stall avoidance.

The original Speed/Mach trim function was created to account for the shift in neutral point as the Mach number increases and decreases, e.g. avoid Mach Tuck (which can kill you). However, over the years is have been expanded to provide a number of additional functions, primarily around speed stability. This is critical at low speed, high AoA where if the aircraft gets behind the power curve and is negatively stable in speed you can rapidly approach stall. STS does this by actively trimming the aircraft to a higher speed than it is currently flying at (eg more nose down). When the 737NG was certified in the mid 1990s the FAA was fine with the handling and stall ID characteristics of the aircraft. However, the JAA baulked at it. The JAA, mainly from the legacy of the UK CAA is very stall averse. As such they required an augmentation system to help identify stall (different than avoidance). This is because the 737 does not have hard envelope limits. Since the NGs behaviour around stall only needs the pilot to let go of the yoke, Boeing got away without using a stick pusher. Instead they made STS even more aggressive as Vs is approached, making it even harder to hold AoA. This effectively makes the aircraft behave like it has a clean stall before it even stalls. Boeing even did a press release about this in 1997. Because of the history of the 737 the STS uses only one Pitot-Static system at a time (I believe there are two computers that can be switched between). Therefore if the pitot-static system fails to a low speed the system will runaway nose down. Boeing use the now infamous 'bad maths' to show that this STS was ok. It turns out that it probably is, even if the pilots are less likely to diagnose it properly and quick as the failure rate of the system is much lower than the original estimates.

Do you think the bit flip issue could be found on the NG as well? I am surprised it is only an issue on the MAX. Not that I think they need to fix it on the NG, but they should just say that the NG is grandfathered in at a lower safety factor if that is the case.

DenverTed
Posts: 385
Joined: Wed Mar 27, 2019 11:12 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

Ertro wrote:
You all look at this issue from benefit of hindsight that was not available at the time when decisions were made. Even if there would have not been any FAA rules affecting landing gear height it is totally possible that Boeing would not have done anything differently.

It is pretty clear that at that moment when major architectural decisions were made about the landing gear and engine placement nobody saw the problems they are going to run into years later and the need to have anything like MCAS at all. All they were set to do was just an easy and cheap minimum upgrade for a plane that is soon to become obsolete anyway with NSA blowing it out from the water after just a couple of years.

Redesigning landing gear was not seen as an easy upgrade so it was left out. Just hang the engines on the wings and that's it. All done. At that time when decisions were made engineers did not see the the problems they are going to run into later like needing MCAS and all what follows. If they would have forecasted everything we can be sure that they would have started doing something differently in a major way already many many years ago.

I'm not sure that the FAA was giving them the option to build a new wingbox, longer gear, and keep all the old substandard stuff and still call it a 737. As Keesje points out, what was supposed to be the threshold of changes for complete review and compliance with current regulations?

PW100
Posts: 4038
Joined: Mon Jan 28, 2002 9:17 pm

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

patrickjp93 wrote:
PW100 wrote:
patrickjp93 wrote:
That the EASA allowed and the FAA did not. They share a treaty to respect each other's certifications, but does not bind either one to follow the same process as the other.

Please list the reasons. This should be fun.

That treaty is the result of 25 years of harmonisation and cross checking.

There is no, I repeat no difference between FAA and EASA when it comes to "iterative improvement". I really struggle to understand where you got that idea from.
Maybe you should check out the number of SBs on B737-800, or CF6 for that matter to understand how much "iterative improvements" thoseFAA certified products underwent.

That's all irrelevant. The processes are not the same, not even close, and we have years of certification threads on here for the A330 NEO, A320 NEO, and 777X. They are different methodologies, though both are logically sound for the most part.

Neither of them received that much iteration at a cursory reading. It's all mostly cosmetic or longevity items apart from a very minor geometry change on engine blades and the split scimitar winglets for the 737 NG.

I you think that's all irrelevant, that really kills off all discussion.

I have worked on the front end both from commercial perspective and aviation authority perspective (organisation design approval, EASA Parts 21J, FAA, TCCA), so I like to think I have some basic understanding in this field.
Immigration officer: "What's the purpose of your visit to the USA?" Spotter: "Shooting airliners with my Canon!"

Posts: 2263
Joined: Wed Mar 01, 2006 4:29 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

DenverTed wrote:
phollingsworth wrote:
DenverTed wrote:
I thought that speed trim was cruise control to trim to constant speed? I had not heard that it was some kind of stall or pre stall avoidance.

The original Speed/Mach trim function was created to account for the shift in neutral point as the Mach number increases and decreases, e.g. avoid Mach Tuck (which can kill you). However, over the years is have been expanded to provide a number of additional functions, primarily around speed stability. This is critical at low speed, high AoA where if the aircraft gets behind the power curve and is negatively stable in speed you can rapidly approach stall. STS does this by actively trimming the aircraft to a higher speed than it is currently flying at (eg more nose down). When the 737NG was certified in the mid 1990s the FAA was fine with the handling and stall ID characteristics of the aircraft. However, the JAA baulked at it. The JAA, mainly from the legacy of the UK CAA is very stall averse. As such they required an augmentation system to help identify stall (different than avoidance). This is because the 737 does not have hard envelope limits. Since the NGs behaviour around stall only needs the pilot to let go of the yoke, Boeing got away without using a stick pusher. Instead they made STS even more aggressive as Vs is approached, making it even harder to hold AoA. This effectively makes the aircraft behave like it has a clean stall before it even stalls. Boeing even did a press release about this in 1997. Because of the history of the 737 the STS uses only one Pitot-Static system at a time (I believe there are two computers that can be switched between). Therefore if the pitot-static system fails to a low speed the system will runaway nose down. Boeing use the now infamous 'bad maths' to show that this STS was ok. It turns out that it probably is, even if the pilots are less likely to diagnose it properly and quick as the failure rate of the system is much lower than the original estimates.

Do you think the bit flip issue could be found on the NG as well? I am surprised it is only an issue on the MAX. Not that I think they need to fix it on the NG, but they should just say that the NG is grandfathered in at a lower safety factor if that is the case.

with NG, service history is a big reason to keep things untouched.
Otherwise STS logic failure / trim runaway and response to that should be reviewed. General narrative we hear so far is that software runaway in NG is stopped by column switches and, as such, can be quickly arrested by pilot's first responce action. Which may or may not be the second good reason to keep NG as-is.

AirBoat
Posts: 53
Joined: Sun Jan 18, 2015 11:58 am

### Re: Boeing 737MAX Grounding, General Discussion Thread, January 2020

patrickjp93 wrote:
Exeiowa wrote:
I remember when I thought after 3 years in my profession I knew everything.....

I don't think I know everything. I think I'm perfectly capable of sitting at the adult table and reasoning through issues just as complex as they do.

Do you know what another good word for experience is? Codified bias.

Sorry could not resist, but I was taught that:
experience is learning by making mistakes.
education is learning by other's mistakes.
So lets rather be educated.
An aircraft or any structure for that matter can not be simply designed by good engineering.
Any structure is designed to strict rules governing loads, safety factors and allowable stresses.
If there is a loading condition that is not covered by design codes, then expert help by leading experts should be obtained.
The reason for not doing structural modifications on the max is that any change will trigger a complete re analysis and design of every single structure, which could take years..

### Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos