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Atlas Air 767 down/Texas

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Atlas Air 767 down/Texas

Old 14th Mar 2019, 22:51
  #541 (permalink)  
 
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Originally Posted by Murexway View Post
Don't know if it's true, but I saw an article yesterday saying that Grieg Feith (former NTSB "Mud Stud") mentioned that "the autopilot was still engaged when the aircraft was on its rapid descent, meaning that the pilots were fighting the automation". As an old timer, I can't imagine sitting there below 10,000, watching the throttles go to 100% and the nose dropping to 49 degrees nose low without disconnecting the automation, deploying the spoilers, and pulling for all I'm worth.
One of the things that may need to be looked into on this is how the 767 control system responds if the pilot pushes the column while the autopilot is engaged. More recent models recognize pilot intervention via significant controller displacement as time to disconnect the autopilot. On older models the autopilot does not immediately disengage in response to pilot input. There may have been a period of time where both Hal and Row 0 were providing significant control inputs. Learning that the autopilot remained engaged would not necessarily mean that Hal was at fault.
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Old 14th Mar 2019, 23:36
  #542 (permalink)  
 
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This event was going on for 18 seconds. I would assume that one or both pilots had hold of the yoke.

I can't imagine that either did dot push the A/P disconnect on the yoke.

Note: I am assuming there is an A/P disconnect on the yoke as on previous Boeing's.
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Old 15th Mar 2019, 00:01
  #543 (permalink)  
 
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Originally Posted by Old Boeing Driver View Post
This event was going on for 18 seconds. I would assume that one or both pilots had hold of the yoke.

I can't imagine that either did dot push the A/P disconnect on the yoke.

Note: I am assuming there is an A/P disconnect on the yoke as on previous Boeing's.
There is an autopilot disconnect button on the yoke and a disconnect bar on the glareshield Mode Control Panel on the classic B-763.

Also, the NTSB release said the throttles went to full power before the pitch over.

I also can't imagine not pulling the throttles and speedbrake lever back with the nose pointed down for whatever reason.
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Old 15th Mar 2019, 01:29
  #544 (permalink)  
 
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Originally Posted by FCeng84 View Post
One of the things that may need to be looked into on this is how the 767 control system responds if the pilot pushes the column while the autopilot is engaged. More recent models recognize pilot intervention via significant controller displacement as time to disconnect the autopilot. On older models the autopilot does not immediately disengage in response to pilot input. There may have been a period of time where both Hal and Row 0 were providing significant control inputs. Learning that the autopilot remained engaged would not necessarily mean that Hal was at fault.
No, I'm sure they were trying everything humanly possible, exactly the way we all would have been. But if the darn automation wouldn't relinquish control, that would be a horrible feeling.
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Old 15th Mar 2019, 02:09
  #545 (permalink)  
 
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Originally Posted by svhar View Post
Why the speedbrake lever? I would rather build up speed and altitude until I figured out what happened.
When you"re 49 degrees pitch down and going thru redline?
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Old 15th Mar 2019, 02:12
  #546 (permalink)  
A4

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??????......er....if I’m pointing down at the ground (let alone 49 degrees down) I’m going to close the throttles, pull the speed brake and pull.....probably the only way you’re going to get any chance of gaining altitude......once you’ve arrested the descent.....

A4 (10,000+ hrs Airbus)
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Old 15th Mar 2019, 03:31
  #547 (permalink)  
 
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Also read that their speed increased from their assigned 230 kts to 430 kts in the descent, and that at impact it was close to 500 kts.
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Old 15th Mar 2019, 03:37
  #548 (permalink)  
 
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Originally Posted by A4 View Post
??????......er....if Iím pointing down at the ground (let alone 49 degrees down) Iím going to close the throttles, pull the speed brake and pull.....probably the only way youíre going to get any chance of gaining altitude......once youíve arrested the descent.....

A4 (10,000+ hrs Airbus)
then do not use the speedbrakes but very slowly, increase pitch and convert your energy into climb.
putting out the speedbrakes increases your load on the airframe even more, increasing the chance of an inflight breakup.
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Old 15th Mar 2019, 07:40
  #549 (permalink)  
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I see that.....but accelerating towards the barbers pole (and beyond) also isn’t going to be great for structural integrity! Additionally, it’s dependent upon how much altitude you have to play with......from 20,000 it’s no issue......from 5,000....different scenario. Does the 777/787 have load factor protection like the Airbus? At least you can pull to the limit with out risking structural integrity (if the aircraft (Bus) is in Normal Law). The 767 would obviously require a more nuanced approach to handling.

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Old 15th Mar 2019, 08:06
  #550 (permalink)  
 
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From around 2000’ and 500 kts it would be pretty much a 3 G pull-up. Moot point though if something is preventing full pitch-up control inputs.
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Old 15th Mar 2019, 11:11
  #551 (permalink)  

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Deliberate act possible. Examination of pilots' histories needed.

This possible cause should be evaluated in the same way as a technical issue. Methodically and objectively.
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Old 15th Mar 2019, 12:12
  #552 (permalink)  
 
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Deliberate act possible.
Well, in fact, almost anything is possible until we hear differently!
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Old 15th Mar 2019, 13:27
  #553 (permalink)  
 
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Originally Posted by Icelanta View Post

then do not use the speedbrakes but very slowly, increase pitch and convert your energy into climb.
putting out the speedbrakes increases your load on the airframe even more, increasing the chance of an inflight breakup.
Can you explain this statement. How do speedbrakes increases airframe load?
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Old 15th Mar 2019, 13:43
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Originally Posted by A4 View Post
I see that.....but accelerating towards the barbers pole (and beyond) also isnít going to be great for structural integrity! Additionally, itís dependent upon how much altitude you have to play with......from 20,000 itís no issue......from 5,000....different scenario. Does the 777/787 have load factor protection like the Airbus? At least you can pull to the limit with out risking structural integrity (if the aircraft (Bus) is in Normal Law). The 767 would obviously require a more nuanced approach to handling.

A4
The Airbus will limit you to two Gís in the situation you describe. The airframe is required to take nearly double that load at max certified weight. 2.5 Gís is the requirement with no damage and 3.75 before structural failure. At landing weights those limits would be even higher.
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Old 15th Mar 2019, 14:18
  #555 (permalink)  
 
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Originally Posted by Sailvi767 View Post
Can you explain this statement. How do speedbrakes increases airframe load?
They move the lift distribution outboard, so if you're pulling 2g with the speedbrakes out the root bending moment will be higher compared to a 2g manouevre with a clean wing.
In any case I doubt you'd still be accelerating if you're pulling 2g+ as the drag would be significantly higher
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Old 15th Mar 2019, 14:56
  #556 (permalink)  
 
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Originally Posted by Old Boeing Driver View Post
This event was going on for 18 seconds. I would assume that one or both pilots had hold of the yoke.

I can't imagine that either did dot push the A/P disconnect on the yoke.

Note: I am assuming there is an A/P disconnect on the yoke as on previous Boeing's.
Yes, there is. The 767 doesn't have "high tech" computer "augmentations." It's a straight-forward, easy airliner to fly. A/T easy to disconnect or override. Autoflight easy to turn off.
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Old 15th Mar 2019, 15:05
  #557 (permalink)  
 
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Originally Posted by Running Ridges View Post
They move the lift distribution outboard, so if you're pulling 2g with the speedbrakes out the root bending moment will be higher compared to a 2g manouevre with a clean wing.
In any case I doubt you'd still be accelerating if you're pulling 2g+ as the drag would be significantly higher
At a given AOA the lift the wing can produce is significantly reduced with the speedbrakes out which would unload the wing. If you pulled to a higher AOA to maintain the same G force it may be possible you would shift the bending moment but I doubt it has much impact.
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Old 15th Mar 2019, 16:02
  #558 (permalink)  
 
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Cornering Speed

Written from a fighter pilot viewpoint. When applying to a transport, there are going to be additional factors to consider such as control hinge moments, wing bending moment, and control system design. (For Airbus FBW, all such decisions have been already made for you.)

With the nose buried downward, and with concern about hitting the ground, you would like to achieve a minimum radius turn, but without tearing the aircraft apart.
The minimum radius turn is generally achieved where max AOA and max allowable G meet on the performance curves.

You can consider using up some of your safety margin when planning what G level to attain. Then look up the performance curves and determine a cornering velocity based upon your most probable gross weight.
Below cornering velocity, you can slightly improve performance by accelerating slightly and pulling into buffet. Above cornering velocity, you must slow down to improve turn performance and meanwhile avoid going beyond your max acceptable G (without a G meter).

Knowing your cornering speed is strictly emergency knowledge and would be used solely to ensure you are not completely out of the ballpark in your pull out efforts.
No doubt, the test pilots and aerodynamics guys can flesh this out better. As I recall, the F-4 cornering velocity was 420 knots. You definitely will not want to be anywhere near that speed when you pull out in your transport.
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Old 15th Mar 2019, 17:42
  #559 (permalink)  
 
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Transport aircraft like the 767 have a reasonably light wing loading relative to fighters. I suspect that at the 230 knots assigned they could generate 3.75G’s. Since there is no where to read G force unless they had recent aerobatic flying that would be very subjective.
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Old 15th Mar 2019, 17:51
  #560 (permalink)  
 
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Originally Posted by Sailvi767 View Post


At a given AOA the lift the wing can produce is significantly reduced with the speedbrakes out which would unload the wing. If you pulled to a higher AOA to maintain the same G force it may be possible you would shift the bending moment but I doubt it has much impact.
Correct. Less lift less load. That is how gust load relief via the ailerons works on the bus.

The interesting question would be, how the speed brakes influence the cornering radius pulling out of the dive. However, even here they won't make things worse I would guess.
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