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Atlas Air 767 down/Texas

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Atlas Air 767 down/Texas

Old 15th Mar 2019, 17:31
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Absolute rubbish. In a nose-low unusual attitude, yes, you should pull the Gs smoothly, and earlier than later (before the speed has a chance to increase further), but never use speed brakes. A G load of 4 (which is well beyond certification limits) will increase stall speed by a factor of two. Suddenly you have a stall speed of 350+ knots and you guys want to destroy the laminar flow further? Iím not sure what to think of the comments here. Iíve never ever heard of this. My opinion is deploying the spoilers in a high-G dive recovery is going to put the airplane in the ground twice as efficiently. But go ahead and think itíll help.
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Old 15th Mar 2019, 18:10
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Originally Posted by FIRESYSOK
Iím not sure what to think of the comments here. Iíve never ever heard of this. My opinion is deploying the spoilers in a high-G dive recovery is going to put the airplane in the ground twice as efficiently. But go ahead and think itíll help.
Have you read @Machinbirds post?
He perfectly explained why in certain circumstances temporarily activating the spoilers can make sense.
They make sense when you are above cornering speed, i.e. when the wing could aerodynamically produce more lift than the structure can take. In that case the radius of the pull up maneuver will increase (or you shed the wings). In that case slowing down will reduce turn radius (yes the spoilers will reduce lift somewhat so that would slightly increase the radius. There is a balance Probably some 20-30 kts above cornering speed you get a net gain with the brakes applied.
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Old 15th Mar 2019, 18:10
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Salute!

@ FIRE
I think what 'bird and I and maybe Henra are saying is there is an optimum speed and gee for best turn radius. The AoA is surprisingly lower than stall AoA for many planes.
Your gee toward the center of the circle is what determines the ft/sec from your flight path a millisecond ago. So stall AoA is great for max lift, maybe gliding, but norrmally comes about at a slower CAS than best turn radius. It's not an intuitive relationship, but we have seen it in many of our lites For example, the F-16 gets best turn at about 360 kt CAS and 9 gees - turn radius of about 1400 feet!!!! . You can get up to 25 degrees AoA slower than that but not at 9 gees.

Without a gee limiter, I would pull for all its worth in a big plane and worry abut ripping the wings off later. Most charts I have seen show overspeed and flutter to be a bigger problem than over gee.

GUms opines...
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Old 15th Mar 2019, 18:48
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Originally Posted by FIRESYSOK
Absolute rubbish. In a nose-low unusual attitude, yes, you should pull the Gs smoothly, and earlier than later (before the speed has a chance to increase further), but never use speed brakes. A G load of 4 (which is well beyond certification limits) will increase stall speed by a factor of two. Suddenly you have a stall speed of 350+ knots and you guys want to destroy the laminar flow further? Iím not sure what to think of the comments here. Iíve never ever heard of this. My opinion is deploying the spoilers in a high-G dive recovery is going to put the airplane in the ground twice as efficiently. But go ahead and think itíll help.
I'm sure you're right when you have acft control, as in a high-angle release. But when your nose is suddenly pointed directly at the ground below 10 and the throttles are stuck at max, popping the boards immediately rather than later may buy you a precious few seconds (and feet) to try and correct the situation. If you can get the nose started up, you can always ease the boards in. But as this accident proved, if nothing else is working, you haven't got much to lose by trying anything and everything.
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Old 15th Mar 2019, 18:50
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Originally Posted by gums
Salute!

@ FIRE
I think what 'bird and I and maybe Henra are saying is there is an optimum speed and gee for best turn radius. The AoA is surprisingly lower than stall AoA for many planes.
Your gee toward the center of the circle is what determines the ft/sec from your flight path a millisecond ago. So stall AoA is great for max lift, maybe gliding, but norrmally comes about at a slower CAS than best turn radius. It's not an intuitive relationship, but we have seen it in many of our lites For example, the F-16 gets best turn at about 360 kt CAS and 9 gees - turn radius of about 1400 feet!!!! . You can get up to 25 degrees AoA slower than that but not at 9 gees.

Without a gee limiter, I would pull for all its worth in a big plane and worry abut ripping the wings off later. Most charts I have seen show overspeed and flutter to be a bigger problem than over gee.

GUms opines...
Never heard of "Gees."
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Old 15th Mar 2019, 18:52
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Originally Posted by Murexway
But when your nose is suddenly pointed directly at the ground below 10 and the throttles are stuck at max, popping the boards immediately rather than later may buy you a precious few seconds (and feet) to try and correct the situation.
Which begs the question, were the throttles still at max all the way down and if so why?

And was the autopilot really on until impact?
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Old 15th Mar 2019, 18:58
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Salute!

Sorry Murex, about the "gees", I am used to phonetically spelling out the force of gravity for those foreign to the aviation world.
'course, that's what many women I have entertained haved exclaimed after a few minutes!

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Old 15th Mar 2019, 20:02
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@Airbubba

Originally Posted by Airbubba
Which begs the question, were the throttles still at max all the way down and if so why?

And was the autopilot really on until impact?
I have the same questions. Since this event was over a span of 18 seconds, I would think that they were man handling the controls and forgetting about the automation running the show.

Just the yanking on the yoke would probably disconnected the A/P and surely someone saw the thrust levers full forward. Especially since they were accelerating from 240KTS to 425KTS.

RGDS
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Old 15th Mar 2019, 20:07
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I still believe that the most effective way to prevent/minimize large speed exceedances would be the extension of the landing gear at the onset ( although the ability for a crewmember to physically reach the gear lever and the time required for extension outside of the design parameters would have probably negated any benefit in this situation...).

If I recall correctly, the 767 doesn't physically limit gear extension above VLo ( I think the override button is there to allow retraction when air/gnd logic would otherwise prevent it, but, extension would be dependent on aerodynamic loads), and, obviously it is not without risks, such as loss of gear doors and attendant hydraulic failures, and an unknown pitching moment at high speed as the gear extends. The gear itself is robust and unlikely to be damaged and more importantly offers a source of "clean" drag without the attendant concerns of varying lift distribution via speedbrakes, etc.,etc...
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Old 15th Mar 2019, 20:10
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I am still thinking about the missing bolt on the horizontal stab actuator theory. If this happened the stab would most likely have moved beyond the design limits and could possibly have caused contact with the elevator control cables resulting in an overload of one of the many pulley quadrants. This would cause the cables to go slack and the elevators to assume and retain any arbitrary position. If there is a control column position channel on the FDR and it does not agree with the elevator position, a probable cause could be stab movement beyond design limits. Once the horizontal stab stalled out due to pitch momentum, the excessive nose down AOA could have a wing area effect on the stab (Due to center of lift and hinge location) to blow it into a nose up position resulting in the final pull up.
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Old 15th Mar 2019, 20:37
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WSJ reporting that pilot error is now suspected as cause of crash.
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Old 15th Mar 2019, 21:17
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Originally Posted by Zlinguy
I still believe that the most effective way to prevent/minimize large speed exceedances would be the extension of the landing gear at the onset ( although the ability for a crewmember to physically reach the gear lever and the time required for extension outside of the design parameters would have probably negated any benefit in this situation...).

If I recall correctly, the 767 doesn't physically limit gear extension above VLo ( I think the override button is there to allow retraction when air/gnd logic would otherwise prevent it, but, extension would be dependent on aerodynamic loads), and, obviously it is not without risks, such as loss of gear doors and attendant hydraulic failures, and an unknown pitching moment at high speed as the gear extends. The gear itself is robust and unlikely to be damaged and more importantly offers a source of "clean" drag without the attendant concerns of varying lift distribution via speedbrakes, etc.,etc...
Seems to me that when pointed down hill at such an angle with the ground rushing at you, generating lift (normal load factor) to turn that flight path vector back up above the horizon is the most critical part of recovering. Adding drag that does not come along with additional lift probably does not help much. Anything that limits achieved "gees" is reducing the chances of escape rather than enhancing them.
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Old 15th Mar 2019, 21:44
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Originally Posted by gums
Salute!

Sorry Murex, about the "gees", I am used to phonetically spelling out the force of gravity for those foreign to the aviation world.
'course, that's what many women I have entertained haved exclaimed after a few minutes!

Gums sends...
There are 2 completely different double entendres at play here, I'm not sure which one you meant but my hat's off if it is both!
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Old 15th Mar 2019, 21:59
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Originally Posted by FCeng84
Seems to me that when pointed down hill at such an angle with the ground rushing at you, generating lift (normal load factor) to turn that flight path vector back up above the horizon is the most critical part of recovering. Adding drag that does not come along with additional lift probably does not help much. Anything that limits achieved "gees" is reducing the chances of escape rather than enhancing them.
A few thoughts.

First, if the speed is below Va and therefore lift is AOA-limited, then you're right and strictly speaking, the boards will further limit lift and therefore reduce the pullout-radius-shrinking normal force. However, without a AOA meter and a confident pilot willing to pull all the way to the limit, it is extremely unlikely that the full AOA lift potential will be used to begin with. In that case, the speed brakes' effect on reducing pullout-radius-growing airspeed, will be overall beneficial.

Second, if the speed is above Va and therefore lift is G-limited, then the speedbrakes will have no negative effect and only positive. Third, with the nose significantly below the horizon, if airspeed is below Va, it will be above it very soon anyway.
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Old 16th Mar 2019, 02:15
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Originally Posted by runner1021
WSJ reporting that pilot error is now suspected as cause of crash.
Here's the article from Andy Pasztor:

Pilot Error Suspected in Fatal Atlas Air Cargo Crash

Investigators exploring likelihood that crew accidentally increased thrust on approach to Houston airport, sources say




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Old 16th Mar 2019, 02:21
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Turbulence causing a pilots hand to push the engines to t/o power and then a massive pitch down control input sounds like the most strange and extraordinary cause of a crash I've read, has to more to it surely?
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Old 16th Mar 2019, 02:30
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"The seemingly disoriented crew failed to regain control—despite commands to pull up from the jet’s high-speed dive—and the wide-body plane plowed into a marshy area".

It would appear that this information came from the CVR. Hard to believe it would take more than a few seconds to get the throttles back to idle and initiate a recovery. Negative G causing sustained forward pressure on the yoke???
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Old 16th Mar 2019, 02:37
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Originally Posted by log0008
Turbulence causing a pilots hand to push the engines to t/o power and then a massive pitch down control input sounds like the most strange and extraordinary cause of a crash I've read, has to more to it surely?
Agreed. The turbulence would have had to further jostle a pilot's thumb to disconnect the A/T.

I hope they can recover some useful info from the CVR.

Last edited by extreme P; 16th Mar 2019 at 02:51.
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Old 16th Mar 2019, 02:46
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Originally Posted by Airbubba
Which begs the question, were the throttles still at max all the way down and if so why?

And was the autopilot really on until impact?
Don't know for sure, but the quote about fighting the automation was from Greig Feith, former NTSB guy (https://aeronauticsonline.com/ntsb-r...air-767-crash/) He must still have contacts on the board, I would think. Supposedly, according to the article, they managed to reduce the pitch to only 20 degrees nose low, but it sure doesn't look like that on the video clip that was posted online showing it just prior to impact. The story originally said that the speed was close to 500 kts at impact, but that part seems to have been edited out of the story now. Sure hope it wasn't intentional.
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Old 16th Mar 2019, 02:50
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This is very hard to believe, Airbubba. Not taking you to task, but very skeptical of Andy the twitter entity.
49 degrees nose down is a non trivial departure from anything remotely resembling normal corrective action in a transport aircraft. It's the kind of pitch angle down that you'd see in an aerobatic display.
While I will await further amplifying information, massive nose down pitch of that magnitude is an over-control that is way out of limits for the flight regime the crew were in: getting themselves set up for a standard approach into an airport.
If my hand bumps the control, engine or otherwise, it takes a certain amount of time of "nobody is near the yoke" for that to go from normal flying to 49 degrees nose down and for that to not be immediately corrected.
We'll see what further NTSB releases reveal.
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