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Atlas Air 767 down/Texas

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Atlas Air 767 down/Texas

Old 22nd Mar 2019, 15:43
  #701 (permalink)  

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Does the 767 have accelerated trim rate with flaps extended?

My brutally condensed account of the Rostov (737) accident is that pushover WITH trim (and flap relief + speedtape confusion) put the AC nose heavy into dive from which the crew then did not have the right combination of alertness, skills and altitude to recover.

If the push came with a sustained nose-down trim, how long for it to become impossible to overpower by the other pilots pull?

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Old 22nd Mar 2019, 16:45
  #702 (permalink)  
 
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Originally Posted by FlightDetent View Post
Does the 767 have accelerated trim rate with flaps extended?

My brutally condensed account of the Rostov (737) accident is that pushover WITH trim (and flap relief + speedtape confusion) put the AC nose heavy into dive from which the crew then did not have the right combination of alertness, skills and altitude to recover.
If the push came with a sustained nose-down trim, how long for it to become impossible to overpower by the other pilots pull?
Is it online somewhere?
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Old 22nd Mar 2019, 16:54
  #703 (permalink)  
 
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Originally Posted by dusk2dawn View Post

And then forgot about it for the next 6000???
I know that's the part that doesn't make any sense.
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Old 22nd Mar 2019, 18:13
  #704 (permalink)  
 
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Originally Posted by V1rhot8 View Post
I know that's the part that doesn't make any sense.
Suspect that the -4g pushover would be a significant factor.
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Old 22nd Mar 2019, 19:00
  #705 (permalink)  
 
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Originally Posted by Feathers McGraw View Post
Suspect that the -4g pushover would be a significant factor.
How is that even possible?

I've been through this illusion many times in IMC and while very convincing, nothing that would cause me to shove a 767 control column to the stops.

And I'm disregarding the mentions of the captain pulling opposite.

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Old 22nd Mar 2019, 19:01
  #706 (permalink)  
 
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With so many hacks in effect anyway, would it make sense to program Hal to not allow any maneuvers that would subject inhabitants of the flight deck to more than +/- 3g of vertical push force? I realize that it could be necessary towards the very end to have leeway. But it seems that in an otherwise normal regime, it should not be possible to achieve it somehow by mistake, as what seems the case here.
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Old 22nd Mar 2019, 19:12
  #707 (permalink)  
 
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Makes sense. Standard on Airbus FBW, since 1986.
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Old 22nd Mar 2019, 19:14
  #708 (permalink)  
 
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Originally Posted by Old Boeing Driver View Post
The systems are split, left and right, but in the override scenario, the operable one still controls all surfaces.
Stupid question: How does one end up in an override scenario compared to a split?
And second: What determines which yoke is overriding which?
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Old 22nd Mar 2019, 19:32
  #709 (permalink)  
 
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I'm having a real hard time with the -4g load, especially in a transport category aircraft designed for -1.0 + safety factor. Even when I hit the -2g limits in an aerobatic, it's really significant.

Edit: in fact does the 767 even have sufficient elevator/stab authority to get itself into that situation, relatively instantaneously?
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Old 22nd Mar 2019, 19:35
  #710 (permalink)  
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Suspect that the -4g pushover would be a significant factor.
I suspect that a -4G pushover would result in a lot of bent 767, a lot of cargo pinned against the ceiling in the hold, and pilots being forced out of their seats, with everything loose in the cockpit pinned against the cockpit ceiling. If that airplane experienced that event, I opine it was hardly flying, or being flown under control, afterward.
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Old 22nd Mar 2019, 21:28
  #711 (permalink)  
 
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Originally Posted by Pilot DAR View Post
I suspect that a -4G pushover would result in a lot of bent 767, a lot of cargo pinned against the ceiling in the hold, and pilots being forced out of their seats, with everything loose in the cockpit pinned against the cockpit ceiling. If that airplane experienced that event, I opine it was hardly flying, or being flown under control, afterward.
Agreed. All the valid talk about inexperienced FO's aside, a -4G push, even as a quick reaction, is insanity.

You would think that would quickly be rectified.

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Old 22nd Mar 2019, 23:37
  #712 (permalink)  
 
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What I find unlikely is the comment that the Captain pulled back so hard he sheared the pins on his control column. I have always been taught on Boeings that you cannot apply excess force to the control column that can result in damage. If the controls are jammed due ice you can pull or push as hard as you physically can. If the Captain and copilot oppose each other there will eventually be a break out and then then the left elevator will follow the Captain’s input and the right elevator will reflect the copilot’s input. This happened on the Egypt Air 767 crash in the atlantic.
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Old 23rd Mar 2019, 00:28
  #713 (permalink)  
 
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Wonder if there are any similarities with Northwest Boeing 720 accident.

ASN Aircraft accident Boeing 720-051B N724US Everglades, FL

The final report on the crash determined the cause of the accident to be the unfavourable interaction of severe vertical air drafts and large longitudinal control displacements, resulting in a longitudinal upset from which a successful recovery was not made.
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Old 23rd Mar 2019, 00:37
  #714 (permalink)  
 
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This latest discussion supports my theory of the stab actuator jackscrew fuselage attach bolt falling out. As the bolt worked its way out to the point where only the threads were engaged with the jackscrew, there would be enough slack to allow an aerodynamically preloaded stab to move slightly stab nose down resulting in a slight pitch up. The PF would instinctively push forward on the column aerodynamically unloading the stab rotational force and allow the bolt to fall out and the stab to rotate stab nose up past its design limit. When the stab moved pat the design limits, contact with the stab structure and the elevator control cables would have compromised the control cable integrity rendering the elevator controls useless. Due to the sudden unexpected negative Gs, the PF would instinctively think they were in a wind shear stall ant push forward on the column and throttles. The other pilot would respond to the precipitous nose down attitude by pulling aft on the column. Being in a sudden loss of control situation, and both pilots equally convinced that their recovery attempt was correct would result in a column disconnect with no resulting elevator movement as the control cable integrity was compromised. When the sudden and severe pitch down occurred, the pitch momentum would allow the stab to stall out. As the pitch down momentum continued, the greater flat square area of the stab forward of the hinge point would push the stab to a stab nose down causing the final pitch up. Look at the picture of the jackscrew and notice no blot or compromise of the attachment lug.
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Old 23rd Mar 2019, 00:37
  #715 (permalink)  
 
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Originally Posted by EternalNY1 View Post
Agreed. All the valid talk about inexperienced FO's aside, a -4G push, even as a quick reaction, is insanity.

You would think that would quickly be rectified.
Just a thought, any g applied is effectively due to a pitch change around the centre of lift/gravity. I think that means a magnified g load at the front of the aircraft, so what is felt on the flight deck is effectively more than the average g felt by the airframe.
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Old 23rd Mar 2019, 01:48
  #716 (permalink)  
 
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Originally Posted by Feathers McGraw View Post
Just a thought, any g applied is effectively due to a pitch change around the centre of lift/gravity. I think that means a magnified g load at the front of the aircraft, so what is felt on the flight deck is effectively more than the average g felt by the airframe.
Oh no doubt about that, a -4G push is putting everyone hard against the restraints and possibly the jumpseater against the ceiling, depending on if they are strapped in.

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Old 23rd Mar 2019, 02:39
  #717 (permalink)  
 
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Originally Posted by EternalNY1 View Post
Oh no doubt about that, a -4G push is putting everyone hard against the restraints and possibly the jumpseater against the ceiling, depending on if they are strapped in.
Against the ceiling until the negative Gs ended, and then forward into the throttle quadrant? A frightening thought.
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Old 23rd Mar 2019, 04:44
  #718 (permalink)  
 
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FO pushes full forward. Captain pulls back and splits the yokes (as designed). So you have a stab trimmed for 240 knots, one elevator full down and one elevator full up. And a lot of power has been added, which of course is "nose up".

That does not result in what the airplane did.
Note that the split elevator system on the 767-300 has a limit of 20 degrees between each side. There is a torque tube in the tail tying the two sides together, but there is an override mechanism on this torque tube which allows independent left/right side movement up to 20 degrees. The column force required to activate this override is 25 lbs at breakout, increasing to 41 lbs at 20 of elevator movement. This is related to the tail stuff. The override at the front (between the columns) is also 25lbs. With no air load, the elevator can move a maximum of 28.5 up and 20.5 down with a full forward and aft movement of the control column. If the autopilot was engaged, they would be fighting the camout springs in the elevator servos (until a camout was detected and the A/P disconnected). On top of all this, you have elevator feel.

You'd need to be a rocket scientist to figure out the cumulative effect of all these devices.

Shear pins? Que?
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Old 23rd Mar 2019, 08:44
  #719 (permalink)  
 
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Originally Posted by Educated Airman View Post
This latest discussion supports my theory of the stab actuator jackscrew fuselage attach bolt falling out.
Do you really think this scenario would look identical on the FDR traces as a full ND Elevator Control column input?
Cue: NTSB are no idiots.
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Old 23rd Mar 2019, 17:34
  #720 (permalink)  
 
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Sorry, I cannon post the link. There is an article on Quora "What-caused-an-Atlas-Air-767-to-crash". For updates and details click on (more)... Among the latest updates regarding the NTSB investigation, the article includes a picture of the recovered jackscrew and its position at impact.
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