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Was MCAS needed?

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Was MCAS needed?

Old 15th Jan 2021, 13:46
  #41 (permalink)  
 
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Originally Posted by chriscrepon88 View Post
Wonder how much longer "blancoliori" will continue to defend Boeing's negligence and tortious actions? Hiding the existence of MCAS until after the first of two crashes? Sounds legit.
I not sure MCAS was hidden. The Brazilian Authority had a differences document for the MAX that listed MCAS as a cat B training item. Forkner was listed as a contributor to the document. Why other states authorities did not have MCAS listed I donít know. But it would be interesting to see what the Brazilian training involved.
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Old 15th Jan 2021, 13:51
  #42 (permalink)  
 
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Originally Posted by vilas View Post
The question was did Boeing had NNC for MCAS? When MCAS itself was not disclosed how will they have a procedure for its abnormality?
Whatís interesting is now that they do have a NNC procedure they donít reference any caution about handling in any flight regime when you end up without MCAS. The tail wagged the dog. The solution was eliminate MCAS. The autopilot doesnít need it and pilots donít need it. But too late for that.
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Old 15th Jan 2021, 13:55
  #43 (permalink)  
 
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They now compare two AoA-vanes anytime so the indication in order to stay away from a stall is more reliable. The whole thing is a move back from fly by wire to manual flying. Mixing two worlds didn't add up.
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Old 15th Jan 2021, 15:18
  #44 (permalink)  
 
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Since he MCAS was there to alleviate longitudinal handling qualities I would have though some sort of note would have been incorporated in some check list to advise what a crew may face with respect to handling qualities upon failure. Some helicopters (S-76 and Blackhawk) had longitudinal handling qualities that didn't comply with FAR's and had what was called a pitch bias actuator (PBA) in order to satisfy the FAR. Experience on the line showed the PBA wasn't necessary and was removed.
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Old 15th Jan 2021, 15:44
  #45 (permalink)  
 
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Originally Posted by jimtx View Post
But it would be interesting to see what the Brazilian training involved.



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Old 15th Jan 2021, 17:58
  #46 (permalink)  
 
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Originally Posted by DaveReidUK View Post
Yes, So what did the Brazilian Authority require GOL to train and check?
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Old 15th Jan 2021, 18:04
  #47 (permalink)  
 
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Originally Posted by megan View Post
Since he MCAS was there to alleviate longitudinal handling qualities I would have though some sort of note would have been incorporated in some check list to advise what a crew may face with respect to handling qualities upon failure. Some helicopters (S-76 and Blackhawk) had longitudinal handling qualities that didn't comply with FAR's and had what was called a pitch bias actuator (PBA) in order to satisfy the FAR. Experience on the line showed the PBA wasn't necessary and was removed.
As far as I can tell there is no note or caution in the new procedure and in the simulator session I don't know if they just RTB with no MCAS and thus don't get into whatever regime it was designed to alleviate. It would seem that they should take the simulator into the relevant handling regime to show the non linear stick force to the crew when they do have a MCAS failure.
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Old 15th Jan 2021, 18:20
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Anyone hazard a guess as to why they didn't try an aerodynamic solution. Let's face it a tab or smallish strake glued onto the upper sides of the nacelles wouldn't look too bad and kill the lift at high AoA? I take it KISS doesn't go far at Boeing.....
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Old 15th Jan 2021, 18:50
  #49 (permalink)  
 
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We went thru this a few years back RVF.

The mods closed the threads to new posts.

Unless they deleted all the posts, you may find some stuff there, but the basic rational was aero fixes deleted the better performance from the new motors and their mounting.
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Old 15th Jan 2021, 19:29
  #50 (permalink)  
 
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Originally Posted by RVF750 View Post
Anyone hazard a guess as to why they didn't try an aerodynamic solution. Let's face it a tab or smallish strake glued onto the upper sides of the nacelles wouldn't look too bad and kill the lift at high AoA? I take it KISS doesn't go far at Boeing.....
Not to contradict the esteemed gums, but they did try aero fixes - various strakes on the inlet and add-ons to the wing. None of them worked sufficiently well to alleviate the loss of stick gradient at high AOA. At some point - with huge barn doors on the inlets to spoil the lift - they probably could have made the aero fix work, but it was deemed impractical due to costs, weight, and fuel burn. Then they tried MCAS and it worked like a charm.
The problem wasn't so much the concept of MCAS, it was the implementation.
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Old 15th Jan 2021, 21:21
  #51 (permalink)  
 
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Thanks, TD......

I got the impression from the Boeing "mole" who I will not name but you can see many posts if we have not deleted them.

If you move that big stab you get a ton of change in pitch moment. The normal mode is small changes for the stab and use changes to the elevator. We saw an extreme example with AF447 when the system moved the stab over and over because the pilot held back stick.

Up to me, I would change the FAA 25 rules to account for mechanical feel at the cockpit and then deal with the Airbus stick that has zero feedback. I flew a few thousand hours in jets with zero feedback that did not come from mechanical connections to control surfaces that then let me know the pressure on them. I estimate that 95% of most commercial jets since 1950 never had direct feel of the control surfaces ever.

I have no problem with the stick getting a little light when approaching a high AoA, but that should be shown to the pilots and if deemed a serious problem , use a pusher and or a horn.

The MCAS was a poorly implemented kludge that should have been dealt with using a waiver for its purpose , but then have procedures for the chance it would go rogue.

Logging.... have a great weekend, and geaux Saints.
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Old 15th Jan 2021, 21:48
  #52 (permalink)  
 
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Gums, in the aftermath of the second MAX crash, I believe it was the Canadian authorities who basically argued for just that - get rid of MCAS and get an exemption for the stick force gradient.
For some reason, it never got any traction with the other authorities.
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Old 15th Jan 2021, 21:55
  #53 (permalink)  
 
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Well sort of. EASA is on the record that the MAX is safe to fly with MCAS (version 2.0) off.
And that is their verdict after recent test flights with their own pilots.

Last edited by Less Hair; 15th Jan 2021 at 22:27.
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Old 15th Jan 2021, 22:19
  #54 (permalink)  
 
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td, "For some reason, it never got any traction with the other authorities."

Perhaps Boeing didn't put this option up front because it wasn't a solution to their $1M/aircraft 'min differences training' incentive.
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Old 15th Jan 2021, 22:38
  #55 (permalink)  
 
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Originally Posted by Less Hair View Post
Well sort of. EASA is on the record that the MAX is safe to fly with MCAS (version 2.0) off.
And that is their verdict after recent test flights with their own pilots.
However MCAS must be operative for dispatch.
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Old 15th Jan 2021, 22:46
  #56 (permalink)  
 
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Originally Posted by PEI_3721 View Post
td, "For some reason, it never got any traction with the other authorities."

Perhaps Boeing didn't put this option up front because it wasn't a solution to their $1M/aircraft 'min differences training' incentive.
This was well after the second crash - when Boeing had conceded that simulator training would be required.
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Old 15th Jan 2021, 23:03
  #57 (permalink)  

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Originally Posted by gums View Post
Up to me, I would change the FAA 25 rules to account for mechanical feel at the cockpit and then deal with the Airbus stick that has zero feedback.
Puzzling. While true it's not a feedback loop, such shorthand description obscures the simple fact that on AB - aerodynamically an entirely conventional craft - to get higher AoA
+ more elevator is needed, achieved by
+ greater stick displacement, for which
+ still increasing force needs to be overcome.
The end result is a fixed correlation between AoA and force on the stick. During a commanded maneuver, the requirement for the A/C to resist a push towards the envelope's edge ever more aggressively is well satisfied.

Last edited by FlightDetent; 16th Jan 2021 at 07:51.
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Old 15th Jan 2021, 23:40
  #58 (permalink)  
 
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Thank you, Detent. You have opened the door we had here long ago.

You have described the basis of the problem most folks have RE: FBW

to get higher AoA
+ more elevator is needed, achieved by
+ greater stick displacement, for which
+ still increasing force needs to be overcome.
The end result is a fixed correlation between AoA and force on the stick. For a commanded maneuver, the requirement for the A/C to resist a push towards the envelope's edge ever more aggressively is well satisfied.
The situation 25 years ago with the ;bus ( most widely used FBW plane by many carriers, and at least two variants), was much more than a simple electric voltage or syncrho angle from a control stick to a servo that moved the elevator or aileron or rudder.

I do not have the tech manual for the 'bus stick, but I do not beleive the 'bus stick had any force feedback nor any change in the gradient for gee command dependent upon AoA or even Q. In short, it was like an old Atari game. You got used to the gee command that your stick movement made after pulling on the stick a few times.

The MCAS requirement was as you described. Higher AoA should required more aft stick. That requirement was based upon decades of conventional aircraft designs and control systems. The Airbus 320 and on changed all that.

Many very educated and experienced pilots and engineers are here from the AF447 threads. They will talk at length about the issuues. I prolly screwed up a few assertions about FBW related to current planes, but I can come back and elucidate at length. Unless we have a Concorde pilot here, or an original Viper pilot, I shall continue to pull rank RE: FBW
RE: for the veterna here of all the commercial planes I have ridden in for 60 years, I shall bow to their experience and knowledge and we can discuss. Many of them have flown the same high performance planes that I flew. Some may even been students of mine.

Gotta go now.

Last edited by gums; 15th Jan 2021 at 23:56.
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Old 16th Jan 2021, 03:07
  #59 (permalink)  
 
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Originally Posted by tdracer View Post
This was well after the second crash - when Boeing had conceded that simulator training would be required.
If Boeing concluded simulator training would be required, what training would that be? Flying the simulator and having MCAS run away and deal with it, then take an airplane without MCAS and land somewhere, and on the way let the crew see how the airplane handled without MCAS in the regime it was supposed to pencilwhip? Lives and money spent over a pencil whip that wasn't needed.
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Old 16th Jan 2021, 07:50
  #60 (permalink)  

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gums Best wishes, sir. I am half-convinced the door better stay shut for the clarity of the nice discussion within the scope of this thread, and definitely so for our weekend enjoyments in the offline life.

If we manage to find some knowledgeable folk later, perhaps there are stones to be overturned still. The shirt I'll be wearing says: "Driver of a Bus (with force gradient on the stick for varying AoA)", colour yet to be determined.

Originally Posted by from zzuf one post below
4. In Direct Law - stick to surface, the aircraft is conventionally stable and requires manual trim operation to trim out forces when the speed is changed. Stick force per G is conventional.
My underline. While FBW could render all the requirements for flight control characteristics not applicable or obsolete, in the particular case of mid 1980s design - the small 'bus - the manufacturer decided and suceeded to design a plane that actually fulfills them. Both in its natural, raw aerofoil form, and as well once the HAL is powered up.

Last edited by FlightDetent; 16th Jan 2021 at 13:44.
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