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Boeing 737 Max Software Fixes Due to Lion Air Crash Delayed

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Boeing 737 Max Software Fixes Due to Lion Air Crash Delayed

Old 12th Feb 2019, 00:02
  #21 (permalink)  
 
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The issue here is that certification rules require that increasing pull pitch controller input must be needed to command ever increasing AOA / normal load factor. Without MCAS there are 737MAX flight conditions where AOA / normal load factor can increase with constant column pull such that the pilot would need to relax the pull force in order to avoid exceeding their target nose up pitch maneuver. This characteristic does not comply with certification requirements and thus MCAS was introduced to assure that a steady increase in AOA / normal load factor requires a steady increase in column pull force.
Putting the certification requirement to one side, would a pilot actually have much difficulty with control if the force required decreased with increasing AoA? Any studies ever done with the difficulty it would impose? I'm thinking Airbus where the pilot has no control force feedback.
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Old 12th Feb 2019, 01:11
  #22 (permalink)  
 
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Boeing favors a relatively simple solution that would primarily reduce the power and, under some circumstances, probably the repetitive nature of the flight-control system in question, called MCAS
This software change seems to actually be worse than doing nothing. Training is the most important corrective action, followed by better MCAS trigger logic regarding disagreeing AoA.
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Old 12th Feb 2019, 01:23
  #23 (permalink)  
 
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Am I right in my interpretation that they will still rely on a single AOA sensor?

It would seem logical at first blush that the only sane fix here for such a critical sensor is to add two more AOA sensors and use a voting system (or other way to sanity-check the data) as per the 747's triple INS setup as RatherBeFlying mentioned above?

It seems that any other solution which still relies on one AOA sensor is likely to simply end up a poor-quality patch job, assuming no other sensor input is available that can be relied upon should the sole AOA sensor go faulty.

/Alex - not qualified to talk on this matter at all, so take my post with the bucket of salt it deserves...
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Old 12th Feb 2019, 01:29
  #24 (permalink)  
 
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Thank you Gums! If I may be so bold: What was the design philosophy on the F-16 early on? Did it require a "chorus" of sensors to pass data on re AOA, airspeed, etc to render a decision?

As with many complex systems it appears to this observer that "post marketing experience" with the 737 Max has uncovered a design flaw....
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Old 12th Feb 2019, 02:51
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Salute averow
Our AoA data for the FBW system used two conical sensors and one hemisphericl probe that used differentail air pressure for pitch, yaw and total pressure. The pressure probe data was decoded in a special box, and the mechanical AoA values were basically sent to the main FLCS computers ( four of them).

I may have to get with one of the guys over on the F-16.net forums to verify my data, but seems I recall middle value logic until down to two sensor input, then the most benign value.
Our system used only three of the computers until one went tits up, and we brought in the 4th. Looking back, we had a very graceful degradation until all was lost.

Unlike the 737, we depended entirely upon the FBW and associated computers that interpreted our control inputs and then moved the control surfaces. But the 737 was supposed to be aerodynamically a "normal" airplane and not intentionally unstable as was the Viper ( below 0.95M +/-).

It looks to me that the newer variations of the 737 are more like the VooDoo I flew a half century ago. That thing got "light" on the stick when you got close to the critical AoA, and if you kept pulling then the plane increasd AoA all by itself with no stick command or even forward stick. Wahoo!!!

The VooDoo had two AoA and gee limiters depending whether you had the autopilot engaged or not. Also had a stick pusher for rate limiting and actual AoA limits. Worked for me. And all that was back in 1965 or so. Our roll "feel" was only some springs and no change if we were at 300 knots or 700 knots. Pitch was helped by a bellows to account for CAS and a bob-weight to help for our pitch rate commands at higher gee. In short, nothing fancy like we see with the 737 feel system and STS and now the MCAS.

Thanks for the questions...

Gums sends...

Last edited by gums; 12th Feb 2019 at 02:54. Reason: typos and readability
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Old 12th Feb 2019, 03:00
  #26 (permalink)  
 
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Originally Posted by ImbracableCrunk View Post
They should put longer landing gear on the 737 so the engines can be a bit farther back. And maybe change the nose so it's a bit quieter. Maybe put some cutting-edge 1970's avionics in it. How about a more pleasing brown color for the cockpit?
how about more rubber and bigger brakes so that it doesnít need more runway than a 767? Oh wait, the gear canít be longer because thatís where the wheel wells are. Maybe fewer humps in the floor and a JS that isnít 90 degrees? How about single channel go around too? The 737 is a brand new record player with a digital display.
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Old 12th Feb 2019, 03:17
  #27 (permalink)  
 
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Originally Posted by FCeng84 View Post
WhatsaLizad - Any low level operation would be with flaps extended => MCAS not operable.
Thanks, FC. Forgot about that part of the system description, but still might be a concern after going to flaps up at 1000' AGL.

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Old 12th Feb 2019, 08:04
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Old 12th Feb 2019, 10:17
  #29 (permalink)  
 
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Old 12th Feb 2019, 13:16
  #30 (permalink)  
 
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Originally Posted by hans brinker View Post
Otherwise know as the B757-NG/NEO/MAX
Originally Posted by Smythe View Post
They did this on the MAX to use the larger engines
Maybe I needed a

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Old 12th Feb 2019, 14:16
  #31 (permalink)  
 
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Gums, Betcha forgot about your downsprings on your VooDoo.
Other than the pusher, it had a lot in common with the Phantom in its design concept.

Overall, when I look at the design concept for the NG and Max, it seems that the control forces can get awfully high, and when you begin to get into cable stretch force levels, you lose control authority.
As FCEng84 pointed out elsewhere, the elevator is hinge moment limited as to how much deflection it can generate and that too limits a pilot's ability to control his aircraft
I have read that when stall AOA threshold is reached, the control system further increases control forces in order to make it harder to pull further into a stall. How do you spell more loss of control authority?
On the surface, it seems logical, but it all works to take away a pilot's ability to control his aircraft.
Does a transport really have to fly like a truck?
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Old 12th Feb 2019, 18:00
  #32 (permalink)  
 
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Time to stop when too many aerodynamic band-aids required

It looks like the 37 has finally been stretched [promoted] to its level of incompetence.

Two possible ways out:
  1. Shorten the 87
  2. Use Embraer 195 as a base design.

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Old 12th Feb 2019, 18:18
  #33 (permalink)  
 
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Originally Posted by RatherBeFlying View Post
Use Embraer 195 as a base design.
Hmmm.

To mitigate the 6-abreast 737's inability to be stretched further, you're going to base a replacement on the 4-abreast Embraer?

How exactly is that going to work?
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Old 12th Feb 2019, 18:37
  #34 (permalink)  
 
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Originally Posted by WhatsaLizad? View Post
Thanks, FC. Forgot about that part of the system description, but still might be a concern after going to flaps up at 1000' AGL.
Hmmm. Does the P8 have this control "assistance" system grafted on/In?
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Old 12th Feb 2019, 18:48
  #35 (permalink)  
 
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Originally Posted by weemonkey View Post
Does the P8 have this control "assistance" system grafted on/In?
Unlikely, given that it first flew 10 years ago and it's based on the NG (737-800), not the Max, so it doesn't have the LEAP engines that have necessitated MCAS.
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Old 12th Feb 2019, 23:07
  #36 (permalink)  
 
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WeeMonkey

Pimped up 737-800 , the P8.
It will be interesting to see what they plan to do low level with it.
The power power coupling with rapid pwr changes is nasty if one is used to a P3 I suppose.
The slow trim with flap up is also an issue if yanking and banking at low level. Gets quite heavy.
I know it is supposed to do most of its work from 30 000 feet , but I suspect we will see them at 100 feet up the fjord as well?
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Old 12th Feb 2019, 23:40
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Originally Posted by DaveReidUK View Post
Unlikely, given that it first flew 10 years ago and it's based on the NG (737-800), not the Max, so it doesn't have the LEAP engines that have necessitated MCAS.
And none of those aircraft listed have external stores or internal bomb bay.....see where I'm coming from?...what else might MrB been up to in the "hell yeah" department.
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Old 13th Feb 2019, 00:08
  #38 (permalink)  
 
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as I vaguely recall- ONE of the requirements by the navy was low level flight in bad weather on one engine- and was demonstrated with a standard 737 prior to contract award.

and see also
https://www.seattletimes.com/busines...ng-submarines/

Boeing’s P-8 is the 737 with missiles, sonar and a specialty in hunting submarines

737-P8 sub hunter article
https://www.seattletimes.com/busines...ng-submarines/

and post numbers 12 and 13 - answer = 200 feet and maybe even lower


737-P8 sub hunter article





Last edited by CONSO; 13th Feb 2019 at 00:19. Reason: provide links
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Old 13th Feb 2019, 00:46
  #39 (permalink)  
 
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Originally Posted by ImbracableCrunk View Post
Maybe I needed a
No, I just wish they kept the 757 as opposed to overstretching the 737, 👍
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Old 13th Feb 2019, 00:49
  #40 (permalink)  
 
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Originally Posted by Smythe View Post
They did this on the MAX to use the larger engines
Well, they had to McGyver an extra hinge/extension thingy in there. There was no room to just put longer legs in there.
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