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Atlas Air 767 down/Texas

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Atlas Air 767 down/Texas

Old 11th Mar 2019, 09:48
  #441 (permalink)  
 
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Originally Posted by pattern_is_full
Lord Farringdon - I actually asked myself that same question. And then gave it further thought.

And the conclusion I came to is: that the NTSB takes a methodical, organized and scientific approach to investigations. They aren't going to go haring off after any particular piece of evidence until they have collected all the evidence (and it appears that, at the time of the video, half the aircraft more or less was still out in the mud.)

It's my impression (with no direct experience) that the NTSB first and foremost sets out to determine exactly what happened - relying on evidence such as the videos and track data and coms we've also seen and heard, and also things we have not seen and heard here (FDR and CVR recordings if available; actual radar returns; impact pattern(s), witness descriptions, clock times, and so on). And only once they are sure they know what happened in detail, move on to investigating how and why it happened (which is where the physical jackscrew will - or won't - come in). At which point they will go over to the hangar where the parts are stored, and start testing any and all theories that have developed, against the physical evidence of aircraft parts recovered. As well as sifting through maintenance and crew records and other specifics.

Of course, at that point the physical evidence may suggest additional ideas, and the investigators may go back to the tapes, to see if there was an anomaly (sound, crew comment, control movement or disparity) that went unnoticed on the first reading.

In short, at this point, nothing "figures highly in their minds" - or doesn't "figure highly in their minds," one way or the other. The jackscrew isn't going anywhere - it can wait.

cf: "confirmation bias" - and read your Thomas Huxley: "Sit down before fact as a little child, be prepared to give up every conceived notion, follow humbly wherever and whatever abysses nature leads, or you will learn nothing."

I don't disagree. My only concern would be if this was a ticking time bomb for the aircraft flying right now. Wouldn't you want to defuse that pretty quick? But then again, it strongly suggests the NTSB are not concerned that it is. They will take it step by step. And so as you say, there the jackscrew will lie until they get to it.
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Old 11th Mar 2019, 10:15
  #442 (permalink)  
 
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While the Jackscrew could be at fault, I'm not convinced it is.
I have a fair bit of experience of them in the manufacturing industry. They work in continuous high speed, high load applications for a decade or more without issue.
When they do fail it usually begins by developing endplay. If that symptom is ignored, they fail by sizing up solid (no amount of force will get them to move) because the balls become wedged in the return tube.
They do not strip and there is no warning,.
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Old 11th Mar 2019, 15:39
  #443 (permalink)  
 
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I noticed the jackscrew attachment lug appears to be intact without the bolt in it. Attachment hardware is usually designed to be stronger than the structures they are installed in. I would have expected that if the jackscrew was separated due to impact, that the bolt, nut and fuselage mounted attachment lugs would be present. It would be interesting to see the bolt and nut and determine if the cotter pin had been installed. It is unlikely but not unheard of for this to occur during maintenance. I had a brake torque ling bolt fall out on a 707 that really made a mess of things upon landing due to a forgotten cotter pin.
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Old 11th Mar 2019, 16:07
  #444 (permalink)  
 
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Deep Stall

This accident has got me thinking about something else, such as putting the speed brakes out to slow down and get down quickly and disconnecting the auto throttle. At level off, forgetting to retract the speed brakes and re engaing auto throttles.. The aircraft could have entered a deep stall and given similar nose down profile as captured by the CCTV. I know the guys at the NTSB have their hands full and wish them all the best in finding the cause of this accident so we can all learn from it.

Last edited by hawkerjet; 11th Mar 2019 at 16:08. Reason: meant auto throttle, not auto pilot
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Old 11th Mar 2019, 17:24
  #445 (permalink)  
 
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Given the rapidity with which the AAIB and BEA gave advice regarding the tail rotor of the helicopter model involved in the Leicester City crash, I would assume that the jack screw will get some publicity if the NTSB think it appropriate.
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Old 11th Mar 2019, 18:11
  #446 (permalink)  
 
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Originally Posted by hawkerjet
This accident has got me thinking about something else, such as putting the speed brakes out to slow down and get down quickly and disconnecting the auto throttle. At level off, forgetting to retract the speed brakes and re engaing auto throttles.. The aircraft could have entered a deep stall and given similar nose down profile as captured by the CCTV.
Why would you disconnect the Auto Thottle? That’s not how it is done.
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Old 11th Mar 2019, 18:32
  #447 (permalink)  
 
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Originally Posted by oceancrosser
Why would you disconnect the Auto Thottle? That’s not how it is done.
Agreed, you might get THR HOLD though.

As I posted earlier, it appears that they were late slowing to 250 below 10 so there may have been some speedbrake use just before the upset.

Still, the B-763 has been using autothrottles and speedbrake for three decades with few problems that I am aware of.
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Old 11th Mar 2019, 18:45
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Originally Posted by Airbubba
Agreed, you might get THR HOLD though.

As I posted earlier, it appears that they were late slowing to 250 below 10 so there may have been some speedbrake use just before the upset.
Throttle hold in descent.... If coming from a dual function mode (FLCH VNAV) autothrottle will go SPD automatically at level off. If speed brakes still out more thrust applied to maintain MCP speed. No need to disconnect autothrottle to get it down - would be back at the stops anyway.
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Old 11th Mar 2019, 18:58
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Salute!

I take it that inadvertant reverser on one or both engines is not a player? Not sure how to get to reverse thrust, but seems someone here can answer real quick.

Gums asks...
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Old 11th Mar 2019, 20:23
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Originally Posted by hawkerjet
This accident has got me thinking about something else, such as putting the speed brakes out to slow down and get down quickly and disconnecting the auto throttle. At level off, forgetting to retract the speed brakes and re engaing auto throttles.. The aircraft could have entered a deep stall and given similar nose down profile as captured by the CCTV. I know the guys at the NTSB have their hands full and wish them all the best in finding the cause of this accident so we can all learn from it.
No one does that on the 767. If you want to go down fast you simple select flight change and the throttles go to idle. If you want to help you can pull them to idle however the auto throttle system is still connected and will add power to maintain speed at the level off. I never saw the technique you mentioned used even once in 15,000 hours on the aircraft.
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Old 11th Mar 2019, 20:28
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Originally Posted by gums
Salute!

I take it that inadvertant reverser on one or both engines is not a player? Not sure how to get to reverse thrust, but seems someone here can answer real quick.

Gums asks...
In the air it's tough unless you short a couple of wires and use a screwdriver outside on the wing.

But just from examining the wreckage the investigators could tell if the reverser(s) were deployed, also the DFDR traces
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Old 11th Mar 2019, 21:20
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Salute. looms!

Thx. Kinda what I thot, but don’t have the documents like my friends here linked to me in the 447 thread.

Reason I asked was it seemed improbable to push over and reach the extreme dive angle without bouncing off the top of the cockpit. So I was considering a uncommaned reverser, then yaw, then roll inverted. Of course, the stab disconnect is also on my mind.

Gums sends....

P.S. Also in Florida in Niceville and watch two pure FBW jets every day, one of which even powers the actuators with electrons. If you look up their demos, they both do things that are aerodynamically impossible, he he.

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Old 11th Mar 2019, 21:28
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I take it that inadvertant reverser on one or both engines is not a player? Not sure how to get to reverse thrust, but seems someone here can answer real quick.
Not familiar with the 767 but if this were the case here I would suspect reverser unlock and deployment would have caused significant yaw as per the Lauda 767 out of Thailand some years back. IIRC in that instance the result was in flight break up. You have very little time to catch it. The video suggests no noticeable roll, pitch or yaw changes.
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Old 11th Mar 2019, 21:32
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And, the Lauda 767 that had the inflight reverser deployment had Pratt engines, the Atlas plane was powered by GE's.
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Old 11th Mar 2019, 22:08
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Originally Posted by cappt
I would estimate at least 3" inches between the nut and upper stop.

Seems a little low. I've revised my earlier estimate downwards:

From 767-300 Maintenance Manual scale diagrams and the known maximum of dimension "A" (26.41 inches), ref AMM 27-41-18, the jackscrew is at least 3 inches in diameter. I see about 1.5 diameters of exposed thread. i.e. 4.5", which is about 0.5 degrees nose up (stabiliser position, not aircraft nose or AOA).
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Old 12th Mar 2019, 01:16
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Auto throttles

OK, guys, I was just looking at different ways the aircraft could have been operated and stalled and that came to mind. My lack of knowledge on the B767 auto throttle system has glaringly showed. I guess thats why we use this open forum, to learn more. Thanks for all the positive comments.
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Old 12th Mar 2019, 16:10
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NTSB reporting column input full forward and engines to full. No conclusion yet, but this certainly narrows the possible causes.
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Old 12th Mar 2019, 16:16
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On Mar 12th 2019 the NTSB provided an update stating:

The wreckage was situated in a shallow muddy swamp area, and the main debris field was oriented east to west and about 350 yards long by about 200 yards wide (figure 1). One engine and some landing gear components were found beyond the main debris field to the west. Less dense components and a large portion of the cargo floated southward and were recovered up to 20 miles away.

The NTSB reported:

Air traffic control communications and radar data indicated the flight was normal from Miami to the Houston terminal area. About 12:30 pm the pilots contacted the Houston terminal radar approach control (TRACON) arrival controller and reported descending for runway 26L; the airplane was at 17,800 ft with a ground speed 320 knots.

At 12:34, the airplane was descending through 13,800 ft, and the controller advised of an area of light to heavy precipitation along the flight route and that they could expect vectors around the weather.

About 12:35, the flight was transferred to the Houston TRACON final controller, and the pilot reported they had received the Houston Automatic Terminal Information System weather broadcast. The controller told the pilots to expect vectors to runway 26L and asked if they wanted to go to the west or north of the weather.

Radar data indicated the airplane continued the descent through 12,000 ft with a ground speed of 290 knots, consistent with the arrival procedure. The pilots responded that they wanted to go to the west of the area of precipitation. The controller advised that to do so, they would need to descend to 3,000 ft expeditiously.

About 12:37, the controller instructed the pilots to turn to a heading of 270°. Radar data indicated the airplane turned, and the automatic dependent surveillance-broadcast (ADS-B) data indicated a selected heading of 270°. The airplane was descending through 8,500 ft at this time.

About 12:38, the controller informed the pilots that they would be past the area of weather in about 18 miles, that they could expect a turn to the north for a base leg to the approach to runway 26L, and that weather was clear west of the precipitation area. The pilots responded, “sounds good” and “ok.” At this time, radar and ADS-B returns indicated the airplane levelled briefly at 6,200 ft and then began a slight climb to 6,300 ft.

Also, about this time, the FDR data indicated that some small vertical accelerations consistent with the airplane entering turbulence. Shortly after, when the airplane’s indicated airspeed was steady about 230 knots, the engines increased to maximum thrust, and the airplane pitch increased to about 4° nose up and then rapidly pitched nose down to about 49° in response to column input. The stall warning (stick shaker) did not activate.

FDR, radar, and ADS-B data indicated that the airplane entered a rapid descent on a heading of 270°, reaching an airspeed of about 430 knots. A security camera video captured the airplane in a steep, generally wings-level attitude until impact with the swamp. FDR data indicated that the airplane gradually pitched up to about 20 degrees nose down during the descent.
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Old 12th Mar 2019, 16:46
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Wow.

The only reasons I can think of that you would 'normally' firewall the throttles down low without a stall warning would be windshear or an EGWPS terrain escape maneuver.
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Old 12th Mar 2019, 17:19
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Salute!

Yeah, Bubba, looks like the CVR will provide more than the gruesome data plots.
I mentioned something to 'bird about a possible crew change of position nd then a bit of turbulence that moved bodies about. I am not ruling that out except for the power change.
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