Colgan 3407 Down in Buffalo

[surplus1]

I have never seen a turboprop autopilot that could adjust the aileron trim, and I doubt that the Q400's will either.

I don’t necessarily disagree with you. Although I don’t know the Q-400 I too doubt that its auto pilot moves aileron trim tabs. If you got that impression that’s my fault for not being clear enough. Let me try another way to explain what I wanted to say.

As you read this please do not think that I’m trying to give you flying lessons or aerodynamic instruction. I do NOT mean that at all. I’m just trying to clarify what I said in the previous posts – and only because some of it caused misunderstanding. I’m not an expert – this is just an explanation of what I wanted to mean in the hypothesis. I’m just sharing my thoughts on this most difficult matter.

As a function of controlling bank (in a turn) or keeping the wings level (in level flight) the auto pilot must have some type of input to the ailerons, or spoilers, or combination of both to be able to control the aircraft about its lateral axis.

I made the presumption that the primary control used for roll in the Q-400 is conventional ailerons. If that is NOT the case, please let me know.

If it IS the case, then the autopilot must have input to the ailerons. As far as I know, this can be done in two ways: a) the autopilot displaces a tab on the aileron, which in turn moves the aileron, or b) the autopilot moves the aileron itself.

Since I agree that control by trim tab is unlikely in this a/c type - For purposes of the hypothesis I presumed the latter to be the case, i.e., the autopilot moves the aileron itself. It does not move an aileron trim tab. If this is wrong, please correct me.

Now flying on autopilot, let’s maintain an altitude and make a turn by commanding a heading change from 270 to 180. The autopilot will raise the left aileron and lower the right aileron to induce the turn. Displacement of the aileron will continue until the bank angle reaches the ‘normal’ as programmed in the autopilot. This is usually twenty-five (25) degrees in T-category aircraft.

At the same time the autopilot will apply back pressure to maintain the altitude and alpha will increase.

When the 25 deg bank angle is reached (on most aircraft) the ailerons will be returned to neutral. In a machine with good stability there will be no overbanking tendency at this bank angle and the wings will not try to ‘level’ themselves. If either one of those things does occur, small adjustments will be made by the autopilot to keep the bank angle as constant as possible.

If anything (such as lots of ice on the left wing) tries to make the bank angle increase, the autopilot will raise the aileron on the opposite wing to prevent it. If the force that is causing the left wing to seek a greater bank angle continues or increases, the autopilot will continue to apply ever increasing aileron displacement to prevent it.

Eventually, the autopilot – not the aileron – will exceed its limits and will no longer be able to apply sufficient aileron to stop the overbanking. If this happens the autopilot will disconnect.

As soon as that occurs the ailerons will neutralize with the slip stream – whatever was causing the over banking will still be there – and the aircraft will roll hard to the left (due to the sudden removal of the right up aileron that was holding the bank angle. [There’s your 46 deg bank angle the initially occurred according to NTSB]

Note. It really doesn’t matter if autopilot disconnect was triggered by something else. As soon as it disconnects the aircraft will roll to the left. The only exception is if it was in level flight at the time of the disconnect.

In a case where the autopilot has moved the aileron by a trim tab, the tab would remain deflected and the bank angle will not increase immediately or by much. The pilot will have to re-trim the ailerons by whatever method is provided in that aircraft type – when he no longer wishes to continue the turn..

That is what I was trying to say earlier. Sorry if I used the term “trim” in the wrong place. If I said that the autopilot was trimming the ailerons I did not mean to imply that it was moving a trim tab on the aileron.

 

[FMEpilot]

Does anybody know if the Non-rev Colgan Capt was riding in the jumpseat?

 

[surplus1]

Since we’re here, let’s move to the elevator which has also caused some problems (because of what I said) for some people.

The Q-400 either has a conventional horizontal stabilizer with hinged elevators, stabilators, or an adjustable horizontal stabilizer.

Normally, transport aircraft do not have stabilators (all-flying tailplanes). Those are usually found on military aircraft capable of supersonic flight, which can’t work with hinged elevators. Of course there is always an exception and one such case that I know of was the L-1011. It uses stabilators for pitch control. There are a couple of light aircraft such as the Piper Cherokee that use stabilators balanced by servo-tabs. Stabilators are controlled by the stick or yoke.

Some aircraft (most commercial jets) have adjustable stabilizers while others have a combination of elevator and adjustable stabilizer. Adjustable stabilizers are moved by the trim system. Elevators are moved directly either by mechanical or hydraulic linkage.

I believe that the Q-400 has hinged conventional elevator moved by hydraulics. Please correct me if I am wrong. The hydraulics part I got from two sources: a) comments in this thread, and b) Bombardiers web site which shows the tailplane with an area of 180 sq ft., which I guessed would make the elevator too heavy to move without boost.

If we have a hinged elevator that’s heavy enough to require hydraulics, then we probably have elevator trim tabs. The autopilot will either move the elevator via its trim tab or by using the hydraulics. I chose the former (tab) as being the most likely. If this is wrong please correct me.

In the scenario – if the aircraft levels at a fixed altitude maintained by the autopilot and the power to hold that altitude is less than required, the autopilot will trim the elevator nose up continuously until balance is achieved, i.e., power required = power available. Airspeed will decrease progressively until it matches the other two. Equilibrium is essential to sustained level flight.

If in that process the airspeed results in entering the impending stall regime (whether normal or reset for icing) – it will trigger the stick shaker and the autopilot will disconnect.

If that happens – what does the elevator do?

If the autopilot used the hydraulics to displace the elevator – will something in the system relieve the pressure and allow the elevator to return to the slip stream?

If the autopilot used the trim tab to displace the elevator – will something in the system reset the tab to neutral and allow the elevator to return to the slip stream?

If the answer to either of those questions is YES – the nose will drop and we go about partial stall (shaker) recovery.

If on the other hand the answer to either one of those questions is NO – the nose will pitch up - further increasing AOA and the pusher will activate. Depending on how much elevator up trim was input by the autopilot prior to disconnect – the pitch up could be quite rapid and extreme.

I believe, in my hypothetical scenario, that the answer was NO and that is why the nose pitched up violently initially. The pusher may overpower the up elevator (I’m uncertain if it can) but elevator position wont change until the pilot inputs manual or electric nose trim to neutralize the elevator.

If the PF doesn’t change pitch trim he will be left to fight the up elevator and the pusher at the same time. In my opinion, that is the most probable of the two. If this had happened to me, I seriously doubt that I would think about trimming right away. That would leave me with a bucking bronco on my hands.

Once again, that’s all my theory of what might have occurred. Educated speculation and no more.

 

[surplus1]

This is an intentional duplicate post. I put it in the wrong thread before.


Read this article

http://online.wsj.com/article/SB123492905826906821.html

This is an excerpt of the first two paragraphs. Reportedly, the source is 'the investigators' (NTSB)

"Investigators examining last week's Continental Connection plane crash have gathered evidence that pilot commands -- not a buildup of ice on the wings and tail -- likely initiated the fatal dive of the twin-engine Bombardier Q400 into a neighborhood six miles short of the Buffalo, N.Y., airport, according to people familiar with the situation.

The commuter plane slowed to an unsafe speed as it approached the airport, causing an automatic stall warning, these people said. The pilot pulled back sharply on the plane's controls and added power instead of following the proper procedure of pushing forward to lower the plane's nose to regain speed, they said. He held the controls there, locking the airplane into a deadly stall, they added."

Now look closely at the second paragraph.

My opinion: A) The first sentence (2nd paragraph) is plausible. B) I do not believe the second sentence. I think the NTSB's assumption is wrong.

This is telling us that when the shaker activated and the autopilot disconnected - the pilot pulled back hard on the yoke, added power and then held the back pressure throughout.

To put it simply, I think that's unadulterated BS!

I believe the NTSB (at present) is misinterpreting the pitch -up data (which aggravated the stall) as being caused by or resulting from incorrect pilot input.

If true this is damning.

It is also the complete opposite of training and I just don't believe it.

In critical situations pilots (initially) automatically react in accordance with their training. When the shaker goes off - you push not pull.

I think that whatever 'investigator' said this is overlooking the nose-up trim induced by the autopilot prior to the disconnect.

It may turn out that mistakes were made by the crew prior to the upset - but I just don't buy that one.

For now I'll stick to my theory of elevator trim as the cause of the pitch up and the progression from shaker to pusher - the initial stall of the wing.

After the pusher took effect and pitched the nose down - then yes - the pilot applied back pressure. But not before.

These folks were flying on instruments. You just can't convince me that any pilot who looks at the ADI and sees a servere pitch-up is going to try to correct it by pulling on the yoke - no matter what noise the shaker might be making.

If this really came from an investigator - then they're doing a lot more "speculating" than anyone in this thread.

 

[DiverDriver]

Surplus you've been around a long time and have lots of time. But this wouldn't be the first time a pilot reacted by pulling in a stall rather than pushing. And it wouldn't be the first time a full nose up trim condition lead to a extreme nose pitch up with no override by a pilot trying to bring the nose down. People do funny things under real stress despite training. But I agree that we should not castigate the crew before a thorough investigation is complete and this investigator does seem to be out of line so far.

 

[q100]

This is an intentional duplicate post. I put it in the wrong thread before.


Read this article

http://online.wsj.com/article/SB123492905826906821.html

This is an excerpt of the first two paragraphs. Reportedly, the source is 'the investigators' (NTSB)

"Investigators examining last week's Continental Connection plane crash have gathered evidence that pilot commands -- not a buildup of ice on the wings and tail -- likely initiated the fatal dive of the twin-engine Bombardier Q400 into a neighborhood six miles short of the Buffalo, N.Y., airport, according to people familiar with the situation.

The commuter plane slowed to an unsafe speed as it approached the airport, causing an automatic stall warning, these people said. The pilot pulled back sharply on the plane's controls and added power instead of following the proper procedure of pushing forward to lower the plane's nose to regain speed, they said. He held the controls there, locking the airplane into a deadly stall, they added."

Now look closely at the second paragraph.

My opinion: A) The first sentence (2nd paragraph) is plausible. B) I do not believe the second sentence. I think the NTSB's assumption is wrong.

This is telling us that when the shaker activated and the autopilot disconnected - the pilot pulled back hard on the yoke, added power and then held the back pressure throughout.

To put it simply, I think that's unadulterated BS!

I believe the NTSB (at present) is misinterpreting the pitch -up data (which aggravated the stall) as being caused by or resulting from incorrect pilot input.

If true this is damning.

It is also the complete opposite of training and I just don't believe it.

In critical situations pilots (initially) automatically react in accordance with their training. When the shaker goes off - you push not pull.

I think that whatever 'investigator' said this is overlooking the nose-up trim induced by the autopilot prior to the disconnect.

It may turn out that mistakes were made by the crew prior to the upset - but I just don't buy that one.

For now I'll stick to my theory of elevator trim as the cause of the pitch up and the progression from shaker to pusher - the initial stall of the wing.

After the pusher took effect and pitched the nose down - then yes - the pilot applied back pressure. But not before.

These folks were flying on instruments. You just can't convince me that any pilot who looks at the ADI and sees a servere pitch-up is going to try to correct it by pulling on the yoke - no matter what noise the shaker might be making.

If this really came from an investigator - then they're doing a lot more "speculating" than anyone in this thread.

Actually, and I've been concerned about this for years, each of the airlines I've been at (including 2 Dash8 operators) trains stall recoveries with the emphasis on holding attitude and powering out. The reduction in angle of attack comes from increased forward speed, not from change in pitch. Completely bass-ackward from the primary flight training we all received where reducing pitch attitude is the first step to recovery. Now I know the theory behind the "airline method" is that the recovery is from the first indications of a stall, but...

The first indication of a stall is usually the stick SHAKER. The pusher might never be experienced in a training environment, unless recovery is slow/delayed. To my knowlege - correct me if wrong - SAAB 340s do not have a stick pusher. It may very well be that the crew had never encountered one in action before. I'm speculating here - only those familiar with Colgan's Q400 program can say if this would have been the case or not.

To go one step further, lets say the crew of 3407 was attempting this maneuver against a stick pusher. To maintain pitch attitude and altitude would require enough back pressure to overcome the pusher. When it breaks away, all of a sudden there's 80 pounds or so of back pressure on the yoke. That could lead, I would think, to a 30 degree pitch up and an accelerated stall rather easily.

Pure speculation I know. But, if it turns out that this was just a case of a tired and distracted (by ice, new aircraft type, unfamiliar airport, high workload approach, whatever) crew getting too slow and then attempting to recover from the stall indications as per simulator training, then I think we pilots need to take a long hard look at stall recovery training and return the emphasis to the most important thing in any stall recovery, reducing the angle of attack.

As a former Dash8 100 driver, can any of you Q400 folks tell me if your stall recovery training in type involved the pusher? Or was it as described above?

Q.

PS: I am not blaming the crew - I don't know the facts of what happened. But if the scenario I laid out did actually take place, I think we have an industrywide need to re-evaluate stall recovery training.

 

[WSurf]

Actually, and I've been concerned about this for years, each of the airlines I've been at (including 2 Dash8 operators) trains stall recoveries with the emphasis on holding attitude and powering out. The reduction in angle of attack comes from increased forward speed, not from change in pitch. Completely bass-ackward from the primary flight training we all received where reducing pitch attitude is the first step to recovery. Now I know the theory behind the "airline method" is that the recovery is from the first indications of a stall, but...

Its because you are training in a 121 Commerical environment. You're not doing full stalls on the commerical level like you did in the underpowered Piper or Cessna.
Its the first indication of stall, the shaker or buffet you are instructed to recover then.
Added power and either leveling your pitch or maybe lowering a bit should get you out of the impending stall easily.

So no, the 'airline method' is not a$$ backwards.

 

[BirdCatcher]

To my knowlege - correct me if wrong - SAAB 340s do not have a stick pusher.

Saab has a stick pusher

 

[q100]

To my knowlege - correct me if wrong - SAAB 340s do not have a stick pusher.

Saab has a stick pusher

thx - next question: would it ever be encountered in training?

 

[LJ45]

from the WSJ:

According to the plane's flight recorders, Flight 3407's descent into Buffalo was routine until roughly a minute before impact, when the crew lowered the landing gear, followed by the command to extend the wing flaps, which enable the plane to fly at slower speeds.
Almost immediately, these people say, the plane's air speed slowed rapidly, causing a stall-warning device known as a "stick-shaker" to cause the pilots' control column to vibrate. This was followed by a "stick-pusher," which automatically forces the stick forward.
At this point, the captain appears to have pulled back with enough force to overpower the stick-pusher and shoved the throttles to full power, according to people familiar with the matter. Safety board officials said the nose pitched up to a 31-degree angle. Already at a dangerously low speed, the wings immediately stopped generating lift. The plane whipped to the left and then entered a steep right turn, losing 800 feet of altitude in less than five seconds. At one point the right wing was perpendicular to the ground, according to information taken from the flight data recorder.
The pilots continued to fight with the controls almost all the way to the ground, and in the final moments, "it appeared that they were beginning to make headway when they ran out of altitude," said one person who looked at the data.