Atlas Air 767 down/Texas

[DaveReidUK]

Despite being misinterpreted (wilfully?), McGinty's post was perfectly clear.

He (or she) did not assert that the wings would fall off in a dive.

[MLHeliwrench]

Reverse control

Say the horizontal stab somehow became able to float up and down the screw shaft on its own - would the elevators act as a servo surface like how some aircraft have a smaller flight control surface move opposite the desired deflection of the main surface?

In this hypothetical scenario, pulling back the yolk would cause the horizontal stabilizer to deflect leading edge up. This would cause a dive.

Can anyone attest to the capability of full yolk back (under normal travel limits) to overcome a horizontal stab trimmed all the way leading edge up?

[B2N2]

Originally Posted by DaveReidUK

Despite being misinterpreted (wilfully?), McGinty's post was perfectly clear.

He (or she) did not assert that the wings would fall off in a dive.

Insinuated the wings would rip off.
Which they didn’t “before the ground interfered”.

[DingerX]

That situation is colloquially known as "over easy".

Through the noise: the relevance of the free fall calculation would have been to get a back of the envelope estimation of what an in-flight break up would look like. The videos pretty much make that exercise pointless. They also make a compelling case for a primary or secondary flight control issue, whether the yolk stayed where it was, got scrambled with the white, or ended up in a nose-down omelette.

[FCeng84]

Originally Posted by MLHeliwrench

Say the horizontal stab somehow became able to float up and down the screw shaft on its own - would the elevators act as a servo surface like how some aircraft have a smaller flight control surface move opposite the desired deflection of the main surface?

In this hypothetical scenario, pulling back the yolk would cause the horizontal stabilizer to deflect leading edge up. This would cause a dive.

Can anyone attest to the capability of full yolk back (under normal travel limits) to overcome a horizontal stab trimmed all the way leading edge up?

I concur with your suggestion that a floating stabilizer would be impacted by the elevators in much that same manner as a tab-driven trailing edge control surface. Airplane nose up elevator deflection puts loads on the stabilizer in the opposite direction and thus would drive a floating stabilizer in the airplane nose down direction. For small motions, elevator has about half as much pitch authority as stabilizer on a degree for degree basis. The story is not quite that simple, however. Below are a few factors to consider:

First is the question of where the stabilizer is positioned for trim. If the stabilizer were near its airplane nose down limit when trimmed and then went to that limit there should be enough elevator to counter. If, however, the stabilizer were a long way from its airplane nose down limit when in trim, having it go all the way to its airplane nose down limit would probably generate more nose down pitching moment than the elevator could counter.

Second is the question of elevator blow-down due to limited hinge moment capability. At approach speed the elevator control actuators are able to generate enough force to drive the elevators to their travel limits. At cruise (and faster) speeds elevator travel will be hinge moment limited as the actuators cannot generate enough force to reach elevator travel limits. This can become a serious issue in a dive as the higher the airspeed gets, the less elevator deflection the system can generate to command the needed pull-up to recover.

Third is the question of elevator effectiveness with the stabilizer at its full airplane nose down limit. With the stabilizer leading edge up (i.e., airplane nose down) it may disturb flow over the elevator in such a way as to reduce elevator effectiveness. This would be particularly true if elevator is at first able to generate nose up pitching moment to generate significant wing AOA needed to pull out of a dive. In that case the AOA seen by the tail will be that of the airplane (i.e., the wing) plus the angle of the stabilizer. If this is high enough, flow over the stabilizer will begin to separate severely reducing elevator effectiveness - particularly in the airplane nose up direction.

The bottom line is that having the stabilizer significantly out of trim is a bad situation. Herein lies the crux of why control systems that require detection and arrest of uncommanded stabilizer motion have requirements to do so within just a couple of degrees of errant stabilizer motion.

[DaveReidUK]

Originally Posted by MLHeliwrench

Say the horizontal stab somehow became able to float up and down the screw shaft on its own - would the elevators act as a servo surface like how some aircraft have a smaller flight control surface move opposite the desired deflection of the main surface?

Bear in mind that when the Alaskan MD-80's jackscrew let go, it pulled through the mechanical stop and just kept going. The elevators didn't make a blind bit of difference.

[Lonewolf_50]

Originally Posted by mustangsally

Maybe that is why I only look at this web sight for entertainment with a couple of pints.

I thought that was a requirement.

@Old Boeing Driver: had there been another aircraft impacting the accident aircraft, I am pretty sure that lost or damaged plane would be accounted for/reported, by now. (So I think I agree with you)

Unless it's a drone at 6000'? (That is a piece of raw guesswork to answer the hypothesis of "something hit the 767" which hypothesis so far neither ATC nor the NTSB has alluded to as a possible cause factor)

PS: thanks for the video, but it also made my guts clench up.

[B2N2]

A lot of things are possible but fewer and fewer are plausible

[Old Boeing Driver]

Originally Posted by Lonewolf_50

I thought that was a requirement.

@Old Boeing Driver: had there been another aircraft impacting the accident aircraft, I am pretty sure that lost or damaged plane would be accounted for/reported, by now. (So I think I agree with you)

Unless it's a drone at 6000'? (That is a piece of raw guesswork to answer the hypothesis of "something hit the 767" which hypothesis so far neither ATC nor the NTSB has alluded to as a possible cause factor)

PS: thanks for the video, but it also made my guts clench up.

The video was gruesome to me as well. By the looks of the speed coming down on the video, I still lean to a failure in the tail somewhere.

Have a great evening.

[Gipsy Queen]

Originally Posted by SteinarN

An object which is free falling is by definition experiencing zero G, this is according to laws set by Albert Einstein.

I suspect that a fellow called Newton thought of this first.

[BluSdUp]

Nothing wrong with the Stab?

So they did 240kts at ca 6000feet.
ATC lost radio and Radar contact.
So problems with Electrics and or Electronics.
Maybe due to turbulence and cargo shift, maybe not?

But as it have been showed in quite a few accidents it only takes a few seconds with the wrong elevator inputs and it is all over.
FlyDubai is case in point, and that Russian 737.300 was the same.
But the Bombardier RJ in Sweden as described in an earlier post was the worst.

Lets for argument sake say they lost a generator or a bus, so that the aircraft was dumped in the hands of PF without any warning!
All it takes is a few seconds of zero or negative G and it becomes critical, THEN depending if they have all displays , You have to be quick and correct in the recovery.
This would also explain why the Transponder stopped working.

There was nothing wrong with the Stabilizer, is my wild guess, mainly because no Boeing to date has had this problem.
Minor OR major problem in Display, AP, Electronics and Electrics, with a small or big human factor problem I am afraid is most likely.
Regardless , a gruesome way to end.
As terrible as this is for friends and family, It could be worse.
It could be a regular passenger flight.
So lets learn.

Peace
Cpt B

[a330pilotcanada]

Good Evening All:

I have been out of the "industry" for about nine years now but I found this link for an Airworthiness Directive for all models of the B-767.

For those who are more up to date than I am please comment.


https://www.federalregister.gov/docu...-767-airplanes

[Skywagon1915]

Any other way to view the video ? I can't open it at all.

[sablatnic]

Originally Posted by Skywagon1915

Any other way to view the video ? I can't open it at all.

It is here on youtube:

You Tube

[lpvapproach]

Those videos appear to show the airplane intact and flying, descending down to the ground

[DaveReidUK]

Originally Posted by a330pilotcanada

Good Evening All:

I have been out of the "industry" for about nine years now but I found this link for an Airworthiness Directive for all models of the B-767.

For those who are more up to date than I am please comment.

https://www.federalregister.gov/docu...-767-airplanes

See post #316 from two days ago.

Originally Posted by DaveReidUK

AD 2008-06-06. Still in force.

[JH_CAMO]

I’m sure people will understand that for professional reasons I can’t post maintenance records online, but the AD line of thought is a bit of a red herring.

Reference my earlier post, this aircraft was in full compliance with all applicable ADs.

Generically I can say that the SB mandated by the AD requires three separate actions - a detailed inspection, lubrication, and a free play check. All of these have been performed on time since the AD was effective.

[ManaAdaSystem]

Originally Posted by BluSdUp

So they did 240kts at ca 6000feet.
ATC lost radio and Radar contact.
So problems with Electrics and or Electronics.
Maybe due to turbulence and cargo shift, maybe not?

Lets for argument sake say they lost a generator or a bus, so that the aircraft was dumped in the hands of PF without any warning!
All it takes is a few seconds of zero or negative G and it becomes critical, THEN depending if they have all displays , You have to be quick and correct in the recovery.
This would also explain why the Transponder stopped working.

Did they loose the transponder?
Where does the transponder get power from on the 767?
On the NG the transponder will work even when you are down to battery power. Is the 767 different?

[DaveReidUK]

Originally Posted by ManaAdaSystem

Did they loose the transponder?

Where does the transponder get power from on the 767?
On the NG the transponder will work even when you are down to battery power. Is the 767 different?

ATC stopped receiving the transponder signal shortly before impact. That doesn't mean it had stopped transmitting at that point.

SSR data captured by FR24 continued up to around 2-3 seconds before the aircraft hit the ground. Allowing for the granularity of the captured data, it's perfectly possible that the transponder was transmitting right up to impact.

[ManaAdaSystem]

Thanks.
And to clarify, it’s transponder #1 that is wired to the battery. If transponder #2 is operating, you need to switch it to #1 if you loose AC power.
Easy to forget in a high stress situation.