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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 23rd Oct 2019, 12:53
  #3361 (permalink)  
 
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Originally Posted by 568 View Post
If the gear was made taller then this may have been an issue with the front air stairs not being long enough to reach the ground.
I dont know if the MAX has air stairs anymore as an option - ? TUI's don't but I think Ryanair have them on their MAX 8-200
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Old 23rd Oct 2019, 13:04
  #3362 (permalink)  
 
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Originally Posted by 568 View Post
If the gear was made taller then this may have been an issue with the front air stairs not being long enough to reach the ground.
The nose gear was made taller anyway, it's the mains that are short (well, same size as they ever were).
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Old 23rd Oct 2019, 13:32
  #3363 (permalink)  
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Originally Posted by edmundronald View Post

We have it on record the the test pilots reported the stick gradient issue and recommended an aerodynamic solution, but were overruled. They were then in the loop on every change and evolution in MCAS as MCAS was a SOLUTION to flight behavior issues. In their role as testers they certainly considered stab trim failure modes. These guys know exactly what the state of play and knowledge was within Boeing at the time of certification. This they are ideal witnesses.

Also, my intuition is they knew things werent quite right eg, stab trim failure could easily become terminal because of the great authority of the stabiliser, and with one quiet word to their FAA contacts over an evening drink, they could have prevented this fiasco.

Edmund
Got it. Thanks. I simply didn't understand your original post.

However, as infrequentflyer points out, just above, the test pilots don't seem to have known as much about MCAS as they should have known.
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Old 23rd Oct 2019, 13:41
  #3364 (permalink)  
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Originally Posted by 568 View Post
If the gear was made taller then this may have been an issue with the front air stairs not being long enough to reach the ground.
I suppose anything is possible, but it's a bit difficult to imagine engineers saying, "We can't lengthen the main gear, because the (optional/aftermarket) airstairs wouldn't be long enough. Let's move the engines, significantly changing the aerodynamics of the airplane, and play around with an add-on to STS."
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Old 23rd Oct 2019, 14:05
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Originally Posted by OldnGrounded View Post
I suppose anything is possible, but it's a bit difficult to imagine engineers saying, "We can't lengthen the main gear, because the (optional/aftermarket) airstairs wouldn't be long enough. Let's move the engines, significantly changing the aerodynamics of the airplane, and play around with an add-on to STS."
Of course, no discussion would be that short but we know that at least some of the decisions were driven by customer desire not to have to pay for extra training so the equation around gear length may have been something like
extra gear length requires $$ extra engineering plus customers wont like it versus we are fitting new engines anyway so why not beef up the s/w to manage the change on aero qualities
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Old 23rd Oct 2019, 14:41
  #3366 (permalink)  
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Originally Posted by OldnGrounded View Post
I suppose anything is possible, but it's a bit difficult to imagine engineers saying, "We can't lengthen the main gear, because the (optional/aftermarket) airstairs wouldn't be long enough. Let's move the engines, significantly changing the aerodynamics of the airplane, and play around with an add-on to STS."
I was informed by a mutual friend on the Renton flight line that this was one of the reasons that the air stairs would have to be changed, plus jet bridges at airports, so that’s what I am passing on.



Last edited by 568; 23rd Oct 2019 at 14:51. Reason: Text
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Old 23rd Oct 2019, 14:51
  #3367 (permalink)  
 
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Yep,
During testing a computer sensed pitch up force was discovered..

This abnormal nose-up pitching is not allowable under 14CFR §25.203(a) "Stall characteristics". Several aerodynamic solutions were introduced such as revising the leading edge stall strip and modifying the leading edge vortilons but they were insufficient to pass regulation. MCAS was therefore introduced to give an automatic nose down stabilizer input during elevated AoA when flaps are up.

14CFR §25.203 Stall characteristics.

(a) It must be possible to produce and to correct roll and yaw by unreversed use of the aileron and rudder controls, up to the time the airplane is stalled. No abnormal nose-up pitching may occur. The longitudinal control force must be positive up to and throughout the stall. In addition, it must be possible to promptly prevent stalling and to recover from a stall by normal use of the controls.
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Old 23rd Oct 2019, 14:52
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The lengthened gear would have required additional certification effort and would probably have lifted the evacuation height from the over-wing exits above 6ft/1.8m, which would have driven a requirement to fit an escape slide.
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Old 23rd Oct 2019, 15:08
  #3369 (permalink)  
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Originally Posted by Maninthebar View Post
Of course, no discussion would be that short but we know that at least some of the decisions were driven by customer desire not to have to pay for extra training so the equation around gear length may have been something like
extra gear length requires $$ extra engineering plus customers wont like it versus we are fitting new engines anyway so why not beef up the s/w to manage the change on aero qualities
Maninthebar, 568, Fortissimo: I get it, folks. I didn't say that it's difficult to imagine Boeing making the choice, rather that it's difficult to imagine engineers making it, as an engineering solution, absent real pressure from the bean counters and marketing team.

Of course, if not for such pressure, engineers would likely not have chosen to try to squeeze out yet another airplane under type certificate A16WE.
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Old 23rd Oct 2019, 15:15
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Originally Posted by Fortissimo View Post
The lengthened gear would have required additional certification effort and would probably have lifted the evacuation height from the over-wing exits above 6ft/1.8m, which would have driven a requirement to fit an escape slide.
Notable we all seem to have heard different things.

Mine was that the existing gear was the maximum that could be folded between the lower fuselage main frame/spar members; any larger gear than the NG and it would have been necessary to do a redesign of the basic structure, seen as not an option.

It was possibly all of the above, in combination.

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Old 23rd Oct 2019, 15:27
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Lion Air crash investigation faults Boeing 737 Max design and oversight
The families of victims in last year's Lion Air crash have been told by Indonesian investigators that poor regulatory oversight and the design of Boeing's 737 Max contributed to the fatal disaster.

Investigators on Wednesday provided victims' relatives with a summary of their final report on the crash, which killed 189 people. Details from the briefing for family members were shared with CNN by Anton Sahadi, a spokesperson for the relatives.

The report summary said that faulty "assumptions" were made during the design and certification of the 737 Max about how pilots would respond to malfunctions by the Maneuvering Characteristics Augmentation System (MCAS), according to the presentation seen by CNN.

MCAS lowers the nose of the plane when it receives information that the aircraft is flying too slowly or steeply, and at risk of stalling. The system was vulnerable because it relied on a single angle of attack (AOA) sensor, investigators said.

The AOA sensor on the doomed Lion Air plane had been miscalibrated during a repair, according to investigators. But the airline's maintenance crews and pilots couldn't identify the problem because one of the aircraft's safety features — the AOA Disagree alert — was not "correctly enabled during Boeing 737-8 (Max) development," they said...

...A spokesman for Indonesia's National Transportation Safety Commission said Wednesday that its final report will publish on Friday.

It has been sent to the US National Transportation Safety Board and other relevant parties, and those parties have replied with comments, the spokesman said.
============
Note:
The Indonesian NTSC investigated that the replacement vane had been a recertified Rosemount Aerospace's AOA sensor which had been serviced by a USA company in Florida. Please read the following news article for details: Faulty 737 Sensor In Lion Air Crash Linked To US Repairer .

- https://edition.cnn.com/2019/10/23/b...air/index.html
- https://www.thejakartapost.com/news/...-repairer.html
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Old 23rd Oct 2019, 15:58
  #3372 (permalink)  
 
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Originally Posted by rog747 View Post
I don't know if the MAX has air stairs anymore as an option - ? TUI's don't but I think Ryanair have them on their MAX 8-200
The initial photos of Ryanair's (first?) "737-8200" appear to have the forward airstairs door.

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Old 23rd Oct 2019, 16:27
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It is indeed an evacuation driven constraint; a longer MLG would raise the wing above the maximum allowed height for non-slide assisted evacuation. Fitting slides would be a major and costly exercise, which Boeing does not wish to entertain. They've even gone to the length of inventing the fancy MLG on the -10, which will extend only at rotatation, then revert to its "folded" position when retracted and remain in that position until the next rotation. All to keep runway requirements below what would otherwise have been, well, a very large and indigestible number.

Internal Airstairs can either be extended or, if that's not possible, discontinued as an optional extra. Passenger bridges are height adjustable (otherwise a 737 Max wouldn't fit a 737NG bridge), as are mobile passenger stairs. A folding mechanism can be engineered, allowing for a longer gear without creating interference in the gear bays. But you can't increase the body height over ground without major revisions, eventually resulting in the loss of a common type rating.
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Old 23rd Oct 2019, 16:30
  #3374 (permalink)  
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Smile

Originally Posted by OldnGrounded View Post
Maninthebar, 568, Fortissimo: I get it, folks. I didn't say that it's difficult to imagine Boeing making the choice, rather that it's difficult to imagine engineers making it, as an engineering solution, absent real pressure from the bean counters and marketing team.

Of course, if not for such pressure, engineers would likely not have chosen to try to squeeze out yet another airplane under type certificate A16WE.
No problem
I know what you were getting at and yes I agree with your comments in full.
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Old 23rd Oct 2019, 17:14
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Originally Posted by SMT Member View Post
It is indeed an evacuation driven constraint; a longer MLG would raise the wing above the maximum allowed height for non-slide assisted evacuation. Fitting slides would be a major and costly exercise, which Boeing does not wish to entertain. They've even gone to the length of inventing the fancy MLG on the -10, which will extend only at rotatation, then revert to its "folded" position when retracted and remain in that position until the next rotation. All to keep runway requirements below what would otherwise have been, well, a very large and indigestible number.

Internal Airstairs can either be extended or, if that's not possible, discontinued as an optional extra. Passenger bridges are height adjustable (otherwise a 737 Max wouldn't fit a 737NG bridge), as are mobile passenger stairs. A folding mechanism can be engineered, allowing for a longer gear without creating interference in the gear bays. But you can't increase the body height over ground without major revisions, eventually resulting in the loss of a common type rating.
I wonder why the maximum allowed height is the one of the NG... seems that some certification parameters have been made to fit existing models and subsequent grandfathering
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Old 23rd Oct 2019, 17:44
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Originally Posted by cats_five View Post
I got the impression from way back in this thread that the physical constraints of the airframe mean the gear is already as long as can be accommodated.
Maybe. I don't think it was explored in the design because doing so would have negated constraints of the prospective buyers.
Given the design constraints, taller gear wasn't an option to even explore.

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Old 23rd Oct 2019, 17:56
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Originally Posted by patplan View Post
MCAS lowers the nose of the plane when it receives information that the aircraft is flying too slowly or steeply, and at risk of stalling. The system was vulnerable because it relied on a single angle of attack (AOA) sensor, investigators said.
If that's really in the report, and not just a bad reporting job, then it contradicts what has been stated about MCAS.

Other repeated inaccuracies too, but that bit caught my attention.
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Old 23rd Oct 2019, 17:59
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Originally Posted by OldnGrounded View Post
I didn't say that it's difficult to imagine Boeing making the choice, rather that it's difficult to imagine engineers making it, as an engineering solution, absent real pressure from the bean counters and marketing team.
Engineers seldom get free reign on design. They deal with design constraints set by company policies and marketing.

That's just life as an engineer, especially at a large company.
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Old 23rd Oct 2019, 18:03
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Originally Posted by FrequentSLF View Post
I wonder why the maximum allowed height is the one of the NG... seems that some certification parameters have been made to fit existing models and subsequent grandfathering
I'd have to research the history of that regulation, but I suspect it predates the NG.
More likely the NG (or even the Classic) was designed to stay under the limit.
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Old 23rd Oct 2019, 18:15
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Originally Posted by ST Dog View Post
Engineers seldom get free reign on design. They deal with design constraints set by company policies and marketing.

That's just life as an engineer, especially at a large company.
Yes, I know -- from experience. OTOH, some companies (sometimes) understand when decisions really should be engineering-driven. Not least because, in the longer term, profits, and more, may depend upon doing that way. The MAX appears to be an example of a failure to understand that.

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