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

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

Old 4th Jun 2019, 12:50
  #161 (permalink)  
 
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Originally Posted by yoko1 View Post
compartmentalization
Key word. The KC-46 team recognized the potential. I can't speak for information sharing within Boeing between development teams. Be curious to know if the MCAS software between the two platforms was designed/developed by the same team.
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Old 4th Jun 2019, 13:36
  #162 (permalink)  
 
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Originally Posted by Smythe View Post
Reading and wordsmithing the Boeing press releases on testing the software fix, and waiting for FAA approval for a validation flight, leads me to believe that much of the "testing" is being done in the sim.
This right there is one of the biggest issues in the whole story. How can you certify a plane according to its sim!?
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Old 4th Jun 2019, 14:37
  #163 (permalink)  
 
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Originally Posted by yoko1 View Post
I think the more germane question is whether anyone actually realized that a single-point failure had been introduced into the design after all the modifications. It appears that there were too many chefs with a hand in the MCAS design and no one stepping back to give it a thorough top to bottom review. We would like to think that during the design phase someone would have seen what has now become obvious to everyone, but given the time pressures and compartmentalization built into the process, I can also see how this might have been missed.
.
It would have to been an oversight at original design of the software
That oversight would have to have been missed by whatever peer review process is invoked within Boeing
Missed when drafting submission for Certification
Missed by Certifying authority
Missed by Boeing when quantum of movement changed (speed/extent of stabiliser deflection) (to be fair this is probably the point at which it would have been least likely to have been spotted)

That's a lot of misses it seems to me. Your question is VERY pertinent and this Human Factors element of the investigation will be interesting to unpick

Last edited by Maninthebar; 4th Jun 2019 at 14:59.
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Old 4th Jun 2019, 14:46
  #164 (permalink)  
 
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Originally Posted by derjodel View Post
This right there is one of the biggest issues in the whole story. How can you certify a plane according to its sim!?
Boeing guarantees, and everyone around agrees, that the 737 sim is perfectly flyable in case of MCAS event.
It's just that the airplane doesn't correctly replicate the sim...
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Old 4th Jun 2019, 15:19
  #165 (permalink)  
 
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As was feared....

Boeing's (BA -1.7%) 737 MAX jets likely will get the green light to fly again by the end of this year, CEO Dennis Muilenburg tells CNBC, while declining to provide a specific timetable.

The company is conducting simulated flights with air safety regulators this week and expects to fly the MAX with the Federal Aviation Administration "very soon" afterward to get the grounded plane cleared to return to service, the CEO says.

Boeing will work closely with customers to repair "damaged trust" of the flying public but this "will take time," Muilenberg says.

emphasis added....
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Old 4th Jun 2019, 15:40
  #166 (permalink)  
 
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Originally Posted by Smythe View Post
As was feared....

Boeing's (BA -1.7%) 737 MAX jets likely will get the green light to fly again by the end of this year, CEO Dennis Muilenburg tells CNBC, while declining to provide a specific timetable.

The company is conducting simulated flights with air safety regulators this week and expects to fly the MAX with the Federal Aviation Administration "very soon" afterward to get the grounded plane cleared to return to service, the CEO says.

Boeing will work closely with customers to repair "damaged trust" of the flying public but this "will take time," Muilenberg says.

emphasis added....
Perhaps Muilenberg could use the example of Lauda and organise himself a ride with erroneous MCAS activation. That would both prove recoverability and demonstrate confidence.

After all, if he wont do it, why should any of the rest of us?
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Old 4th Jun 2019, 16:36
  #167 (permalink)  
 
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Perhaps Muilenberg could use the example of Lauda and organise himself a ride with erroneous MCAS activation. That would both prove recoverability and demonstrate confidence.

After all, if he wont do it, why should any of the rest of us?
Absolutely! Anything short of this is disingenuous.
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Old 4th Jun 2019, 17:44
  #168 (permalink)  
 
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Salute!

"As was feared....." Uh huh. No need to see the real deal. No need to conduct tests that fail things in conditions that the engineers never thot of. You know...... at high alpha ( not speed!!!!).

Chuck Wannabe, "this new plane has a light stick when close to the stall"
.
Non-pilot engineer, "No problem, we can crank the stab up a bit so it's harder to pull back to a higher AoA ( NOTE!!! not speed, but AoA). In all the Boeng FCOM stuff I have accessed, the term "speed" is used lots more that AoA. yet MCAS and the stall shaker use AoA as the primary driver. Even STS is named "speed xxx xx" Yet AoA in most condiitions determines the need for trim, or am I too old? And isn't AoA that determines stall regardless of gee or true airspeed or bank angle or.......

Pilot, "errrr, what about the elevator feel system, won't it make it harder to pull back ?".

Engineer, "nope. apparently moving motors and doing other stuff reduces longitudinal pitch moments when a few degrees AoA below stall., and the feel system uses airspeed more than AoA"

Pilot, "why use the stab to increase back stick force versus the existing elevator feel sytem that affects the column?

Engineer, "well, the EFS uses speed more than AoA. You know, the old dynamic pressure we call "q" that the FBW folks use for what they call "gains" and you guys call indicated airspeed or pounds per foot squared or ..... there must be fifty ways......"

Pilot, "Oh, but what about the increasing back column force if the AoA is really high, and not just due to "q"?"

Engineer, : Hmmmmm...... may have to fly another test flight or two or three........"

Gums sends...
P.S. Wait until you see my questions at the trials of the survivors WRT mis-management and possible negligence resulting in a few hundreddeaths. @ mods..... maybe need a thread over on Tech Log, huh? We all appreciate your patience and apolitical stance thus far in this debacle. Salute!

Last edited by gums; 4th Jun 2019 at 20:09.
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Old 4th Jun 2019, 18:46
  #169 (permalink)  
 
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Originally Posted by Smythe View Post
Boeing's (BA -1.7%) 737 MAX jets likely will get the green light to fly again by the end of this year, CEO Dennis Muilenburg tells CNBC, while declining to provide a specific timetable.
Is that the first we have heard of this date now from official sources ? December ?

https://www.cnbc.com/2019/06/03/boei...-ceo-says.html
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Old 4th Jun 2019, 19:31
  #170 (permalink)  
 
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Originally Posted by WHBM View Post
Is that the first we have heard of this date now from official sources ? December ?

https://www.cnbc.com/2019/06/03/boei...-ceo-says.html
The Emirates airline president Tim Clark dropped a big hint at the recent IATA meeting: https://www.reuters.com/article/us-a...-idUSKCN1T301Z
Clark warned it could take six months to restore operations as other regulators re-examine the U.S. delegation practices - though U.S. majors have only suspended MAX schedules to August.

“That is why it is going to take time to get this aircraft back in the air. If it is in the air by Christmas I’ll be surprised - my own view,” he told reporters.
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Old 4th Jun 2019, 21:38
  #171 (permalink)  
 
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Originally Posted by PiggyBack View Post
The thing is that however good the legendary pilots of yesteryear it is far safer now than in the past. I think there is a lot of selective memory and golden age fallacy going on.

I am not going to rehash the problems with MCAS but this was clearly behaviour of a system in the event of a single fault with a probability of a catastrophic outcome that was not small. You can argue that in the past the excellance of pilots meant that they would on average have handled it better, but it is irrelevant, it would still have a significant chance of causing a crash and it would still be considered an unacceptable design that must be rectified.
And if you look at the legendary crashes of yesteryear, quite a number were caused by flightdeck negligence. Need I recite them?

Originally Posted by sky9 View Post
OK just an old fart but:
In the 1970's the company I joined demanded 2000 to sit in the right hand seat of a 737 (...).
Currently how many hours to sit in the right seat (the Ethiopean F/O Ahmed Nur Mohammod Nur, 25 had 361 hrs) [...].
But if the '70s F/O had spent 1,000 hrs teaching amateurs like me to fly single-engine VFR and the Ethiopean F/O had gained 150 hours as part of training at a flight academy for airline pilots, which of these sums is the better preparation for the job?

I've heard there are today 200-hr pilots out there flying nuclear-armed aircraft. If true, what does that mean?
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Old 4th Jun 2019, 22:08
  #172 (permalink)  
 
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Salute!

Careful there, VFR.

Lottsa difference in supervision and such besides total flying hours for the military folks. Figure about 200-250 hours of military training and then to the buff or nuke capable attack plane. Oh yeah!!! How many hours do the missile folks have that sit 100 feet underground and can launch a dozen ICBM's?

In my own case, I had about 500 military hours when I first sat nuclear alert up north waiting for the horde of Bears and Bisons destined for Chicago, Kansas City, St Paul, Detroit, and such - the "central flyway".No offense to our Russian folks here, as we all know what was going on back then 50 years ago. I was an Air Defense Command interceptor pilot.

The difference is that the military crew is not flying a nuclear mission several times a week and has tons more supervision and cross checks than a nugget civilian regional route pilot.

So let's get back to the issue here that will have a dramatic influence on all commercial aircraft development and testing. Huh?

Make no mistake. The Boeing 737 MAX certification process and their engineering solution of an aerodynamic problem is gonna have a long lasting and serious impact on Boeing as well as the entire commercial industry. Just me speaking.

Gums sends...
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Old 4th Jun 2019, 22:18
  #173 (permalink)  
 
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When in doubt , add vortex
tabs
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Old 4th Jun 2019, 22:26
  #174 (permalink)  
 
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VFR

Just for the record , there is 125hrs pilots starting the Line training in Europe as we speak.
Many are good , most are not.
All are up to standard and the standard is to low.

Do not confuse this with Military training, please.

So ,how come FAA demands 1500hrs for 737 and Europe 120hrs.
Trust me , it is not a good idea!

BTW
I am looking forward to see the Max training requirement.
Ps Training is defined as Sim or Flight, can anyone tell Boeing and the Authorities!

Regards
Cpt B
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Old 5th Jun 2019, 00:30
  #175 (permalink)  
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Originally Posted by Smythe View Post
When in doubt , add vortex
tabs
it often appears to be the solution, but not so much in this case.

VG's generally control separation, or introduce shock forming structures into the boundary layer.

The general problem with the Max is change in the Cp on the wing around the engines at varying AOA, that is the result of the lift being generated by the nacelle. There may be some interference effects from the nacelle at low AOA that add to the relative shift and that would be able to be altered by VGs, but otherwise not going to do much there. A possible solution would be to reduce the strake effectiveness on the nacelle, but that comes with total lift penalties over that gained at present for modest AOA values.

The Stab itself is not going to benefit from VG's.... The elevators may, for low profile VGs that are well forward on the elevator surface, which would improve elevator authority at high deflections, but then that also results in a load change that may affect the existing stick force per G which is the symptom that is being dealt with. Increasing elevator authority can improve the controllability against a jammed stabiliser, but that does not benefit directly freeing up the stabiliser itself when it has become immovable due to aero loads when using manual trim. Trailing edge tabs, as T, L's or ramps increase the elevator authority (thickening the TE), but that is the same outcome, improved control margin over the jam, but no change to the immovable stab case directly. Presumably sufficient elevator authority would permit getting the plane to a condition where the crew can then unload the control system sufficiently to permit manual trim in the period that the aircraft is following the incorrect trim. Maybe.

VGs' are not certainly the solution in this case, there is a fair bit of CFD needed to sort out the underlying issue, and then a whole bunch of playing with the subsequent control forces to ascertain the real extent and solution of the problem, if, and only if it is considered that having a stab that cannot be controlled due to excessive airloads in manual mode is a bad thing. I still think it is, in the absence of training and analysis of the operational envelope safety that comes along for the ride of this phenomena.

The kludge is that the operators should be aware of the issue, and should ensure that they never get that far out of trim, but sods law is that crews won't stay in that area at all times. As it is an underlying characteristic of the design of the B737 particularly, where a manual backup exists, then it is a product related issue, but, I hazard to guess that the fundamental issue of a locked stab from airloads floats nearby all trim systems, and the margin in actuator force required would bear looking at for other types as well to ensure that the emperor has clothes.
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Old 5th Jun 2019, 02:42
  #176 (permalink)  
 
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Engineer, : Hmmmmm...... may have to fly another test flight or two or three........"
Correction: Hmmmmm...... may have to sim test another flight or two or three....

@fdr...I was being factitious. In reference to the NYT article, the test pilot found the aircraft had issues with low speed stall...he recommended adding VG...engineers said software..

my point being, in the beginning, the 747 had low speed stall issues on initial test flights, they added vg tabs to the wings as a 'temporary measure". (and never left)
now, vg tabs continue on Boeing wing designs, as well as showing up in odd places as 'fixes' such as in front of the windscreen....

hence my comments..

Flight test shows stall issues....

Old school Boeing test pilot: "add vortex tabs"

Millennial engineers: 'add software"

Where does the part about "design wings correctly" come in?

Last edited by Smythe; 5th Jun 2019 at 02:53.
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Old 5th Jun 2019, 03:40
  #177 (permalink)  
 
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Where does the part about "design wings correctly" come in?
That's the heart of this whole issue, there is no design. If this was a clean sheet aircraft none of the problems with the MAX would have existed
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Old 5th Jun 2019, 08:14
  #178 (permalink)  
 
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Originally Posted by Maninthebar View Post
.
It would have to been an oversight at original design of the software
That oversight would have to have been missed by whatever peer review process is invoked within Boeing
Missed when drafting submission for Certification
Missed by Certifying authority
Missed by Boeing when quantum of movement changed (speed/extent of stabiliser deflection) (to be fair this is probably the point at which it would have been least likely to have been spotted)

That's a lot of misses it seems to me. Your question is VERY pertinent and this Human Factors element of the investigation will be interesting to unpick
There were a lot more misses than this starting with the specification of the MCAS system itself. Often this sort of issue is caused by a change the effect of which is not fully assessed and understood invalidating an earlier safety analysis. I am really just speculating but in this case it seems to be change after change after change without a fundamental reappraisal of the effect on safety. This should be the subject of an in depth review to make sure that lessons for the developoment process are learnt.

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Old 5th Jun 2019, 08:22
  #179 (permalink)  
 
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Originally Posted by Smythe View Post
Old school Boeing test pilot: "add vortex tabs"

Millennial engineers: 'add software"

Where does the part about "design wings correctly" come in?
But the wings were correctly designed. The engines were designed too large, or undercarriage designed too short - take your pick.

They had to extend the nose gear for all Max and design and certify a magic folding link thing on the main gear for the -10, I'm not sure why they didn't just do that job properly and give -8/-9 and -10 long enough legs to put the engines same place as the NG so that it flew like the NG, with no need for crazy software bodges.

I think the root of the problem will turn out to be the modelling/simulation at the very start of the process, this was what lead them to believe that they could just mount the engines forward and up a bit, and the only resulting problem was it got a bit light on the stick in a small part of the envelope - so just tweak software to nudge the stab if anyone ever goes there, job done.

It was a brilliant plan with only one teeny tiny flaw - the modelling was bcks. Over confidence and over promise on schedule meant that by the time they found that out they were in a corner where the only possible "fix" looked like changing that nudge on the stab to a full blown miles-out-of-trim yank, and over large areas of the envelope based on only on sensor. Cross fingers, collect bonus, and hope it doesn't break too often and that the regulator won't notice (if we don't tell)...
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Old 5th Jun 2019, 10:38
  #180 (permalink)  
 
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that they could just mount the engines forward and up a bit, and the only resulting problem was it got a bit light on the stick in a small part of the envelope - so just tweak software to nudge the stab if anyone ever goes there, job done.
Once again, that part of MCAS was not the issue from what we know so far. It was that ONE FAILED AOA vane could cause MCAS to activate. THAT was the issue. A software fix is fine, the fact that it could operate on erroneous data from a single source is not.

If you don't like software "nudging the stab" up or down then I guess you hate Tailstrke Avoidance inputs right? Or Airbus Alpha floor? Or Embraer stall avoidance?
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