Colgan 3407 Down in Buffalo

[M-crit]

What would be considered a nominal speed in this config?

With gear down and flaps 5, I would not be slower than maybe 160 or 165, perhaps even faster especially with the ref speeds increased in icing conditions. You would have to be below 181 for flaps 10, or below 172 if you wanted flaps 15.

 

[JetSpeed219]

The increased ref speed switch increases by 15kts. And 134kts for gear down is very slow. Gear is usually coming down around 180. Somewhere around 150 is when flaps 35 is usually selected too.

 

[Papps]

Hate to speculate, but since we are speculating anyway. Is it possible there was a tail stall. as the nose dropped the crew yanked back to correct from tail stall, the tail regained lift, rapid pitch up followed by a wing stall and spin.

 

[glasspilot1]

The reports are that the deice system was turned on. Question for those that fly this airplane: When you turn on the deice system do all the boots activate at once? Or do the wings blow, and then the tail later? I'm just wondering if the wings had been cleared but the tailplane was still iced.

 

[EdAtTheAirport]

Where are you guys getting this spin notion from? I looked at a Q yesterday, and FWIW could not imagine an airplane with that big a tail, on that long of a moment, entering a spin. I could be wrong of course.

 

[WSurf]

The reports are that the deice system was turned on. Question for those that fly this airplane: When you turn on the deice system do all the boots activate at once? Or do the wings blow, and then the tail later? I'm just wondering if the wings had been cleared but the tailplane was still iced.

Its automatic, it sequences from the wings and tail. Works well, there is a knob to select Fast or Slow in the cycling. Also on the Captains overhead panel are the lights that light up once each boot inflates showing you that the system is up and running. Piedmonts Procedure is to Put it on Fast mode anytime you are in icing.

 

[M-crit]

Piedmonts Procedure is to Put it on Fast mode anytime you are in icing.

That is a great idea btw. Why put it on slow? I hope we will be able to find out where the crew had that switch set to- fast or slow.

 

[surplus1]

Colgan 1549 follow up

Surplus 1 said:

As the aircraft levels, the auto-pilot trims nose up to hold the altitude as the speed decreases. The nose up trim continues slowly unnoticed by the crew. The auto pilot is also inducing aileron trim at the same time – to keep the wings level - also unobserved.

Could this accident have been avoided? YES – but not after the upset occurred.
hypothetical.

*****

Well thought out scenario..., doesn't even require any real effects from ice. Be interesting to see what the power setting was while decelerating, while the autopilot held altitude towards the FAF (did they decel into the stall driving in?) Didn't notice the decaying airspeed and approaching stall condition until the high AOA kicked off the autopilot just prior to stick shaker & upset? Full power on the engines hung from the wings (upon stick shaker as first warning to crew) cause initial pitch up?

ILS23 FAF at BUF just under 1500' AGL 4.4 miles from the threshold... upset the aircraft at that altitude and there is no recovery.[/quote]

Thanks for all of your inputs - everyone.

I may have been a bit too vague. The hypothetical scenario was intended to include ice contamination of the airfoil - most probably asymmetrical ice. This would produce stall speeds and critical AOAs significantly higher and lower respectively than normal. The asymmetrical accumulation would induce the autopilot to apply aileron to keep the wings level. I doubt this would have happened in an ice-free environment.

In the hypothetical scenario, auto pilot disconnect is not commanded. [I believe that is consistent with the reports we have so far, i.e., the auto pilot disconnected itself.] It occurs because the autopilot has exceeded its limits (either in roll or pitch or both). My own belief is in roll.

Those who have pointed out that in a tailplane stall the pitch would be nose down are correct. While I didn’t deal directly with that in the hypothetical, I think it was an error on my part that doesn’t fit what we know now – which I did not know at the time.

Given the reported sequence of excursions (pitch and roll) that have since been posted – if they are accurate – I personally do not believe that there was a tailplane stall in this accident sequence. I now believe that the wing stalled. I also believe that one of the two wings stalled before the other. That does NOT mean that I think I am correct. It just means that the available information is pointing my thinking in that direction.

The more information that comes out, the more I see this upset as being remarkably close to the upset sequence that happened to Comair 3272 on its approach to the Detroit area. Up to this point the only major difference I note is the altitude. In the CMR event they were at about 4000 ft (don’t remember exactly) when the upset occurred. If I recall correctly, the time lapse from upset to impact was 17 seconds – based on FDR data.

In this accident sequence - When the autopilot disconnects the nose pitches up immediately (due to the unobserved up elevator trim that I mentioned in the 1st post) and the wing immediately exceeds the critical AOA and stalls. At the same time, one wing stalls more than the other (due to the ice – I believe) and the aircraft rolls in that direction - primarily because the only thing that has been keeping that wing from dropping was the control pressure (aileron) applied by the autopilot.

That would leave us with this unanswered question: What made the autopilot disconnect? I obviously do not know but I do have a theory.

There was a lot of ice on the airplane – much more than the crew realized. There was more ice (for some reason) on the left wing than on the right wing – perhaps behind the boot; Enough to make the left wing drop and the aircraft turn to the left. The autopilot applies enough aileron to prevent the turn (keep the aircraft from banking) or if in a turn, to keep the bank angle from exceeding the norm (about 25 degrees on auto pilot). So far so good.

Note: Shortly before this all happened the aircraft was reportedly vectored to a heading of 260 and cleared for the approach. That appears to comply with the 30 degree localizer intercept angle that controllers are required to give. Continue.

As the aircraft captures the localizer, the autopilot makes another left turn to the inbound heading (I have no plate – but let’s say 230). The autopilot studiously accomplishes this turn. It relives the pressure and the aircraft banks to the left. That’s what it is supposed to do. [All the while more ice is accumulating].

[As you review this keep in mind that both wings don’t necessarily stall at exactly the same time. If one wing is flying and a part of the other is not the aircraft will roll in the direction of the wing that is partially stalled.] Continue.

The next thing the autopilot has to do is stop the turn and hold the localizer. To accomplish this it must apply enough aileron to raise the left wing. It tries but the left wing is heavy with ice and it doesn’t come up. The autopilot tries harder - until it reaches and exceeds its limits. At that instant – the auto pilot disconnects itself.

If this assumption is correct, the aircraft immediately rolls hard left. At the very same time the auto pilot (previously) induced elevator up forces take effect and the nose pitches up hard (+31 deg. according to the reports.)

[Keep in mind that most of us have never seen more than 30 pitch up in actual flight. Perhaps in simulators but not otherwise. This is not ‘normal’ in T-category aircraft. Even if it were, it would not happen suddenly and unexpectedly].

The excursion is so rapid that both shaker and pusher activate almost simultaneously. [The prior post says +31 nose up and 46 deg (left) wing low.]

At this point the upset has occurred and there is really nothing the crew can do to recover within the available altitude. Of course that doesn’t mean that they stop flying. To the contrary – they react immediately in an effort to recover from the unusual attitude.

Taken completely by surprise, the PF (pilot flying) grabs the yoke, moves it full forward and at the same time applies full right aileron to raise the left wing. Full power is applied. [The power application helps to increase the nose up tendency and the PF fights it – as is natural].

The nose rapidly drops through a 76 deg. arc to a -46 deg. nose down pitch and the aircraft accelerates. PF applies up elevator (a whole lot of it) to stop the excessive pitch down. The nose comes up rapidly but most of the aileron input is still there (not consciously). A secondary stall (accelerated) occurs (shaker/pusher activate again) with the aircraft rapidly rolling (almost if not snapping) to 105 deg right bank angle [technically that's partially inverted].

In the effort to recover, control movements are extreme. There is much over-controlling. That's not pilot error, it's to be expected under those conditions. The PF will always be a little behind the aircraft's reaction to control input – this is acrobatic flight but it is not intentional. All of these things occur in 5 seconds or less. Remember - they are not visual - this is all on instruments.

I've never flown the Q-400 or its predecessors. I don't know what if any limits the attitude instrument may have. Are they capable of normal function in acrobatic flight? Can it maintain accuracy with a 105 deg bank angle? Some can, others can't. How much pitch excursion does it take to make the presentation illegible? I have no idea. Can the back up gyro handle that? I don't know. The AS indicator is probably a tape - is it easy to read or does everything become hieroglyphics in the process? I don't have those answers.

You ask: "(did they decel into the stall driving in?) Didn't notice the decaying airspeed and approaching stall condition until the high AOA kicked off the autopilot just prior to stick shaker & upset?"

I think the answer to that question is YES – they decelerated gradually into the stall regime. Why did that happen? Not too difficult.

There was no reason to believe that the airspeed indication was critical. They were intentionally decelerating and IAS was well above stall (under normal conditions) - under normal conditions. Note caveat: I have no idea what a ‘normal’ approach speed for the Q-400 might be but 134 kts does appear to be somewhat slow at the OM (with zero flap) for an aircraft of that size – by about 40/50 knots.

But, conditions were NOT normal. There was likely a great deal of ice on the airframe - in places that they had no way of seeing or knowing. Critical AOA was much lower and stall speed much higher than 'normal'.

Continued below

 

[surplus1]

Continuation

My educated guess is that the autopilot did not disconnect because of the up elevator trim or because it was kicked off by high AOA. I say this because the reports indicate that the autopilot disconnected before the shaker/pusher activated. If that is correct - It disconnected because its ability to control the bank angle had exceeded its limits. That’s my theory – and that’s all it is; a theory.

When the disconnect occurred, the nose up elevator trim caused the initial pitch up. That pitch up caused the wing to stall - very suddenly and immediately.

The reports tell us that an attempt was made to retract the flaps (and maybe the gear). If that is true – it was mostly likely because the PF associated flap extension with the upset. In any event in stall recoveries in this category of aircraft Training often says “max power, flaps up, gear up”. Again, I have no idea what that airline teaches, so that thought is pure speculation. In any case I consider it to be essentially irrelevant in this instance.

Again, I know nothing about this a/c type but my guess is that the elevator trim is electric - and there is no trim wheel in the airplane (something I personally find objectionable – just a quirk of mine). Therefore, it is especially difficult to tell where the elevator trim may be at a given point in time, especially at night in a dimly lit cockpit, when the a/c is being flown by the auto pilot, holding altitude, undergoing power changes and decelerating – all at the same time.

An upset in a transport category airplane is simply not recoverable at an altitude of 1500 ft AGL; certainly not on instruments and totally unexpected. Most if not all upsets are never anticipated.

The very best among us have worked experimental upset scenarios in simulators trying to develop satisfactory recovery techniques (down in MIA if I recall correctly). They developed some ideas but no real solutions and no brilliant recovery technique. Unless there is a great deal of altitude below you, the only thing they managed to prove was that upsets in T-category aircraft are not recoverable. They must therefore be avoided by all possible effort.

Avoidance isn’t cut and dry. Each aircraft is different and one size just doesn’t fit all. Likewise, Icing is a different ball game in each machine. As someone before me pointed out: “In aviation there are three types of ice: Good Ice, Bad Ice and Hazardous Ice.
Good Ice is found in the galley”.

This is NOT the first incident or accident to result from an upset. Perhaps it is the first in the Q-400 but that aircraft can't be so unusual that it 'can't happen'. We all know Murphy’s Law.

Several upsets have occurred in the Brasilia. At least two that I know of resulted in accidents, one of them as tragic as this one. More than one has resulted in structural damage. ALL occurred while the airplane was being flown by the auto pilot and several in VMC. There have been several in versions of the ATR, especially the -42, at least one of which was also a fatal accident in this country. Its obvious or should be, that these new generation turboprop aircraft require their own rules of operating technique and flight crew understanding. The results indicate that some of the invented simulator scenarios just aren’t cutting the mustard. We just can’t keep repeating the same thing over and over an hoping for different results.

It should also be noted that upsets have occurred in heavy jets as well and in small jets too – also involving autopilot operations and situational awareness.

Unless we choose to make ourselves aware of history and act differently as a result of our knowledge, history will surely repeat itself.

It is not my purpose to affix blame or to be critical of anyone. Its not about blame, its about cause and effect.

It is my purpose to do whatever I can to avoid unnecessary repetition of tragedy or even white-knuckle operation. I am willing to err on the side of safety in that effort. I also believe in the axiom – knowledge is power.

If you see error in this phase 2 hypothetical please point it out. I won’t be embarrassed if I’ve made a mistake. At this point I am willing to rule out the tailplane stall theory.

“Aviation in itself is not inherently dangerous. But to an even greater degree than the sea, it is terribly unforgiving of any carelessness, incapacity or neglect.” — Captain A. G. Lamplugh,
PS. Sorry for being so long winded.

 

[bailout]

The part i dont get, is if there were no pitch control input changes prior to the AP disconnect, why would it pitch up? They were already trimmed for level flight (pitch) and possibly coming out of the initial intercept turn (roll), but still 'in level trim', so if the roll excedence were to cause the disconnect, it seems that the pitch shouldnt change? I think i understand when you say that when they were slowing the trim was compensating for the required trim until it reached a limit but usually when you get a AP disconnect because of limits, the plane stays where it was, whether it be level pitch, or in a 20 degree bank turn, or what have you because thats where it was when it disconnected.. Granted you have to take immediate control to prevent something from happening further. You might be right about the wing stall but the nose would dive and the pilot would yank bank which would address the pitch up reports.

 

[VF45]

If you cob the power with full nose up trim, will the Q400 pitch up?

 

[glasspilot1]

Its automatic, it sequences from the wings and tail. Works well, there is a knob to select Fast or Slow in the cycling.

Thanks for the reply Surf.

 

[surplus1]

The part i dont get, is if there were no pitch control input changes prior to the AP disconnect, why would it pitch up? They were already trimmed for level flight (pitch) and possibly coming out of the initial intercept turn (roll), but still 'in level trim', so if the roll excedence were to cause the disconnect, it seems that the pitch shouldnt change? I think i understand when you say that when they were slowing the trim was compensating for the required trim until it reached a limit but usually when you get a AP disconnect because of limits, the plane stays where it was, whether it be level pitch, or in a 20 degree bank turn, or what have you because thats where it was when it disconnected.. Granted you have to take immediate control to prevent something from happening further. You might be right about the wing stall but the nose would dive and the pilot would yank bank which would address the pitch up reports.

As I see it, the key to your statement is in the first sentence: "The part i dont get, is if there were no pitch control input changes prior to the AP disconnect, why would it pitch up?"

Actually there were lots of pitch input changes - all made by the auto pilot and unobserved by the crew. [If the darn airplane had a trim wheel they might have noticed it turning] Additionally, the autopilot was struggling to keep the wing from increasing the bank angle (due to the ice on that wing), which they also did not know.

The aircraft was in a descent - through 6000, 4000 to 2300. Power most likely retarded for the descent. Altitude is pre-selected to 2300.

As we reach 2300, altitude captures and is held by the autopilot. What happens now to airspeed? Unless power is added, airspeed will decrease.

If the autopilot was NOT engaged, and you didn't touch the yoke - what would happen to the nose as the airspeed decreases? It would drop off wouldn't it? If you did not want that to happen but you still wanted to slow down. what would you do? Trim nose up.

Now put the autopilot back in the equation. You told it to hold 2300 ft, and it does. As the airspeed decreases how does it do that? It trims the elevator nose up, to hold the altitude.

If you do nothing else it will continue to trim nose up and the airspeed will continue to decrease - until one of the two reaches the level required to hold that altitude with that amount of power. In other words, if the power available matches the power required to hold altitude at that speed, the auto pilot will stop triming and you will be in level flight with x amount of nose up trim and y amount of power - stable. If the power available/used remains less than required - airspeed will continue to deteriorate slowly until the auto pilot runs out of available trim capability or you exceed the critical AOA and stall.

I am only saying how it works - not what they did. I assume that they added enough power to hold the desired speed (or what they thought would hold it).

Everything is now stable and the auto pilot has stopped triming nose up -but - it has NOT removed much if any of the trim previously input. You're still at 2300 ft and headed for the localizer. Glide slope is not alive and has not captured.

As you approach the localizer the autopilot begins a turn to capture it. The auto pilot is still flying. What happens now?

As the bank increases more back pressure is required to hold the altitude. The auto pilot provides in by additional nose-up elevator trim. Something else also happens - the airspeed begins to deteriorate (slow) again. You decide to accept the slightly lower airspeed and you don't add more power - it's already where you think you want it.

Meanwhile bank angle is increasing and elevator is trimming nose-up (slowly). Bank angle tries to increase beyond 25 deg. (due to the ice) until the auto pilot exceeds its limit and kicks off. The nose pitches up and the wing stalls.

Instantly the bank increases from 25 to 45 degrees - further increasing the stall speed. What happens to stall speed as bank angle increases? Yep, its higher than in was before. It was already on the edge - you just didn't know it.

Just as you act to correct the bank the wing stalls. You call for full power and all that up elevator trim is still there. Where does the nose go before you can stop it? All the way to +31 degrees nose up and you have the yoke full forward. There's a lot of power there and some very big props.

Down goes the nose - very rapidly. Your control input has taken effect There is still too much elevator trim for that amount of power and you're pushing hard.

The instant you see 45 degrees nose down you reverse the pressure and pull like hell. You still have almost full aileron cranked in to pick up the left wing. You havent thought at all about trim. Who would?

Just as you apply that back pressure you now enter an accelerated secondary stall. The aircraft snaps to the right - exceeding the vertical bank angle. It is completely out of control - plus you just lost a thousand feet.

The rest ...............

It's all hypothetical ... just a theory.

 

[surplus1]

If you cob the power with full nose up trim, will the Q400 pitch up?

I've never flown it so I don't really know.

But, if it reacts like other propeller airplanes that I've flown the answer is yes. It would nose up even if the elevator trim was neutral. It's a prop/thrust line thing. Plus it's a high wing, which ususally aggravates that tendency.

 

[trainer8]

Hi Surp,

Very good assesment--your last couple posts. I concur with your assesment, except on a couple minor points.

1) Chealander confirmed AP disconnect occurred at stick shaker/pusher and not from AP sensory loads.

"The NTSB's Chealander confirmed that the autopilot was engaged until the stick-shaker, and the stick-pusher kicked in, signaling the start of an event that could have, and did have dire consequences. He went on to say that when this happens, the autopilot automatically disengages, putting the aircraft back in the hands of the pilot."

2) I wouldn't rule out tailplane icing. Having flown this type for 8100 hours in various icing conditions including moderate icing (tennis ball size ice sculptures on the ice detection probes on an ILS into SWF), it's ability to fly in moderate ice never produced any aerodynamic instability while accreting ice. I would be very surprised if the NTSB ruled that this would be the cause.

The application of wing flap (Dash-8s have full span wing flaps) from 5 to 15 appears to have induced the upset, which fits the NASA tailplane icing flight testing scenarios. (http://www.part135.com/TailplaneIcing.html) Chealander (NTSB) also indicated that the flight crew followed all AFM procedures pertaining to flight into known icing conditions.

What seems to be conspicuous was the situational awareness of airspeed degradation to onset of stick shaker.

Overall, I think your assessment is very good.

T8

 

[belchfire]

Does anyone have the flight and duty times for the crew for the days leading up to the accident date?

The reports tell us that an attempt was made to retract the flaps (and maybe the gear). If that is true – it was mostly likely because the PF associated flap extension with the upset. In any event in stall recoveries in this category of aircraft Training often says “max power, flaps up, gear up”. Again, I have no idea what that airline teaches, so that thought is pure speculation. In any case I consider it to be essentially irrelevant in this instance.

You are doing some very good presentation but my training has been to not change configuration until the stall recovery is complete-though I am not familiar with the Dash either.

With upwards of what, around 10,000shp(?) and those big props my guess is that while application of max power is probably called for in stall recovery training that about 50-70% torque and maintaining a level flight pitch attitude would be enough to recover.

 

[surplus1]

Hi Trainer,

I've only ridden in a Dash 8/200 once in my life. EYW-MIA many years ago. I've never even seen a live Q-400; just pics.

Your points 1 and 2 are important especially # 1. I think the time line here - the exact moment of auto pilot disconnect - is very important. If it is true that the autopilot did NOT disconnect until AFTER the shaker activated, then I would modify my hypothesis to something I have not wanted to say.

That would be that the aircraft reached 2300 ft, with insuffient power to sustain level flight. It slowed gradually - with the auto pilot trimming nose up - unobserved by the flight crew until the shaker activated disconnecting the auto pilot - followed by a stall.

This would mean that the stall speed - with the ice - [as re-programmed by the crew] had increased to somewhere around 130 kts. (given that NTSB says CAS was 134 kts on the FDR) and activated the shaker disconnecting the auto pilot. It would explain the pitch up - and cause the actual aerodynamic stall. But, it would also point to what none of us want to hear = PE.

The initial roll off would simply be a by-product of the stalled wing (1st stall) and the 2nd the product of the accelerated secondary stall. This would NOT be good for the crew.

On your point #2 - I know that if there's ice on the wings there is also ice on the tail. However, the manufacturer claims that flight test data indicates that the Q-400 is NOT susceptible to tailplane stall.

Personally I'm just not ready to buy into the tailplane stall theory, although I'm very much aware that the manufacturer will launch into full CYA mode if it believes that's necessary. Manufacturers never voluntarily admit design anomalies.

If you're right about #1, then I hope I am wrong about #2.

Good to see you.

 

[LJ45]

wish the NTSB would say what the power setting was at time of stall !!! Looking more and more like they were too slow and coupled with some residual ice let the airplane stall. I think if the NTSB would just tell us what the airspeed trend was right before the upset, the power setting and the speed at which the stall warning activated we would have much better info.

 

[surplus1]

You are doing some very good presentation but my training has been to not change configuration until the stall recovery is complete-though I am not familiar with the Dash either.
[/color]

Do you train in a jet? Or something like an L-188, DC-6/7? If so your training is the same as mine has been.

My training experience in the smaller propeller airplanes has been the opposite. I didn't agree with it but I didn't get to make the rules.

 

[trainer8]

Hi Trainer,

I've only ridden in a Dash 8/200 once in my life. EYW-MIA many years ago. I've never even seen a live Q-400; just pics.

Your points 1 and 2 are important especially # 1. I think the time line here - the exact moment of auto pilot disconnect - is very important. If it is true that the autopilot did NOT disconnect until AFTER the shaker activated, then I would modify my hypothesis to something I have not wanted to say.

That would be that the aircraft reached 2300 ft, with insuffient power to sustain level flight. It slowed gradually - with the auto pilot trimming nose up - unobserved by the flight crew until the shaker activated disconnecting the auto pilot - followed by a stall.

This would mean that the stall speed - with the ice - had increased to somewhere around 130 kts. (given that NTSB says CAS was 134 kts on the FDR). It would explain the pitch up but would also point to what none of us want to hear = PE.

The initial roll off would simply be a by-product of the stalled wing (1st stall) and the 2nd the product of the accelerated secondary stall. This would NOT be good for the crew.

On your point #2 - I know that if there's ice on the wings there is also ice on the tail. However, the manufacturer claims that flight test data indicates that the Q-400 is NOT susceptible to tailplane stall.

Personally I'm just not ready to buy into the tailplane stall theory, although I'm very much aware that the manufacturer will launch into full CYA mode if it believes that's necessary. Manufacturers never voluntarily admit design anomalies.

If you're right about #1, then I hope I am wrong about #2.

Good to see you.

My assesment differs only because of my experience flying and teaching the same Type, only smaller, less powerful models.

Watching Chealander's report on Saturday, he was clear about the stick shaker induced/automatic AP disconnect. That unfortunately means the crew was unaware of airspeed degradation and suddenly had a hand-full of tempest. Q400's have 5 panel glass cockpits. Manual trim (big wheels) were changed out for electric trim for this model.

I'm sure Vref is indicated (green dot on the airspeed tape for some aircraft) in some way to the crew. Perhaps others can comment. I hope I'm wrong. But, ATC and NTSB cursery indications are level flight at 2300' approaching KLUMP (FAF) to AP disconnect.

T8

 

[belchfire]

Do you train in a jet? Or something like an L-188, DC-6/7? If so your training is the same as mine has been.

My training experience in the smaller propeller airplanes has been the opposite. I didn't agree with it but I didn't get to make the rules.

Jet now, Jetstream before...

I double checked my current manual before I made my statement and it's clear on the point-don't change configuration of gear or flaps until stall recovery is complete.

I don't have my Jball manuals with me to check them-if I recall correctly it was the same thing-but that little bugger recovered so quickly with full power that it wasn't but a few seconds before the wing was flying again and one would be cleaning up. The little beast was also more stable with the gear out and had wild pitch changes between flaps 20 and 35.

 

[trainer8]

ABC News reported quoting the NTSB that the Captain had 110 hours total hours in Q400, having previously flown the Saab 340.

T8

 

[Flyin2low]

Hi Trainer,

I've only ridden in a Dash 8/200 once in my life. EYW-MIA many years ago. I've never even seen a live Q-400; just pics.

Your points 1 and 2 are important especially # 1. I think the time line here - the exact moment of auto pilot disconnect - is very important. If it is true that the autopilot did NOT disconnect until AFTER the shaker activated, then I would modify my hypothesis to something I have not wanted to say.

That would be that the aircraft reached 2300 ft, with insuffient power to sustain level flight. It slowed gradually - with the auto pilot trimming nose up - unobserved by the flight crew until the shaker activated disconnecting the auto pilot - followed by a stall.

This would mean that the stall speed - with the ice - [as re-programmed by the crew] had increased to somewhere around 130 kts. (given that NTSB says CAS was 134 kts on the FDR) and activated the shaker disconnecting the auto pilot. It would explain the pitch up - and cause the actual aerodynamic stall. But, it would also point to what none of us want to hear = PE.

The initial roll off would simply be a by-product of the stalled wing (1st stall) and the 2nd the product of the accelerated secondary stall. This would NOT be good for the crew.

On your point #2 - I know that if there's ice on the wings there is also ice on the tail. However, the manufacturer claims that flight test data indicates that the Q-400 is NOT susceptible to tailplane stall.

Personally I'm just not ready to buy into the tailplane stall theory, although I'm very much aware that the manufacturer will launch into full CYA mode if it believes that's necessary. Manufacturers never voluntarily admit design anomalies.

If you're right about #1, then I hope I am wrong about #2.

Good to see you.

I'll vote for point #1 and #2 and raise you point #3 (ABC News reported quoting the NTSB that the Captain had 110 hours total hours in Q400, having previously flown the Saab 340.)

NTSB Identification: DCA94MA027 .
The docket is stored on NTSB microfiche number 52866.
Scheduled 14 CFR
Accident occurred Friday, January 07, 1994 in COLUMBUS, OH
Probable Cause Approval Date: 4/12/1995
Aircraft: JETSTREAM 4101, registration: N304UE
Injuries: 5 Fatal, 2 Minor, 1 Uninjured.The airplane stalled and crashed 1.2 nautical miles east of runway 28L during an ILS approach. The captain initiated the approach at high speed & crossed the FAF at a high speed without first having the airplane properly configured for a stabilized approach. The airspeed was not monitored nor maintained by the flightcrew. The airline had no specified callouts for airspeed deviations during instrument approaches. The captain failed to apply full power & configure the airplane in a timely manner. Both pilots had low flight time and experience in in the airplane and in any EFIS-equipped airplane. Additionally, the captain had low time and experience as a captain. Inadequate consideration was given to the possible consequences of pairing a newly upgraded captain, on a new airplane, with a first officer who had no airline experience in air carrier operations, nor do current FAA regulations address this issue.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
(1) An aerodynamic stall that occurred when the flightcrew allowed the airspeed to decay to stall speed following a very poorly planned and executed approach characterized by an absence of procedural discipline; (2) Improper pilot response to the stall warning, including failure to advance the power levers to maximum, and inappropriately raising the flaps; (3) Flightcrew inexperience in 'glass cockpit' automatic aircraft, aircraft type, and in seat position, a situation exacerbated by a side letter of agreement between the company and its pilots; (4) The company's failure to provide adequate crew resource management training, and the FAA's failure to require such training; (5) The company's failure to provide adequate stabilized approach criteria, and the FAA's failure to require such criteria; and (6) The unavailability of suitable training simulators that precluded fully effective flightcrew training. Note: Items 1, 2, and 3 were approved by a Board vote of 4-0. Item 5 was adopted 3-1, with the dissenting Member believing the item was a contributory cause. The Board was divided 2-2 on items 4 and 6, two Members believing them causal and two Members, contributory. (NTSB Report AAR-94/07)

 

[Singlecoil]

Another idea on why it rolled left first:

What happens when you go from idle to full power in a propeller-driven airplane that doesn't have counter-rotating props?

You need to stomp down on the right rudder hard, or the airplane will be uncoordinated. Remember departure stalls when you didn't use enough right rudder? Which way did the stall break?

 

[bailout]

As I see it, the key to your statement is in the first sentence: "The part i dont get, is if there were no pitch control input changes prior to the AP disconnect, why would it pitch up?"

Now put the autopilot back in the equation. You told it to hold 2300 ft, and it does. As the airspeed decreases how does it do that? It trims the elevator nose up, to hold the altitude.

If you do nothing else it will continue to trim nose up and the airspeed will continue to decrease - until one of the two reaches the level required to hold that altitude with that amount of power. In other words, if the power available matches the power required to hold altitude at that speed, the auto pilot will stop triming and you will be in level flight with x amount of nose up trim and y amount of power - stable. If the power available/used remains less than required - airspeed will continue to deteriorate slowly until the auto pilot runs out of available trim capability or you exceed the critical AOA and stall.

Everything is now stable and the auto pilot has stopped triming nose up -but - it has NOT removed much if any of the trim previously input. You're still at 2300 ft and headed for the localizer. Glide slope is not alive and has not captured.

As you approach the localizer the autopilot begins a turn to capture it. The auto pilot is still flying. What happens now?

As the bank increases more back pressure is required to hold the altitude. The auto pilot provides in by additional nose-up elevator trim. Something else also happens - the airspeed begins to deteriorate (slow) again. You decide to accept the slightly lower airspeed and you don't add more power - it's already where you think you want it.

Meanwhile bank angle is increasing and elevator is trimming nose-up (slowly). Bank angle tries to increase beyond 25 deg. (due to the ice) until the auto pilot exceeds its limit and kicks off. The nose pitches up and the wing stalls.

Instantly the bank increases from 25 to 45 degrees - further increasing the stall speed. What happens to stall speed as bank angle increases? Yep, its higher than in was before. It was already on the edge - you just didn't know it.

Just as you act to correct the bank the wing stalls. You call for full power and all that up elevator trim is still there. Where does the nose go before you can stop it? All the way to +31 degrees nose up and you have the yoke full forward. There's a lot of power there and some very big props.

Down goes the nose - very rapidly. Your control input has taken effect There is still too much elevator trim for that amount of power and you're pushing hard.

The instant you see 45 degrees nose down you reverse the pressure and pull like hell. You still have almost full aileron cranked in to pick up the left wing. You havent thought at all about trim. Who would?

Just as you apply that back pressure you now enter an accelerated secondary stall. The aircraft snaps to the right - exceeding the vertical bank angle. It is completely out of control - plus you just lost a thousand feet.

I understand everything you are saying here, except for this: are you saying the nose pitched up when AP disconnected or after they added full power?

I completely understand the nose up pitch change if they added full power after the disconnect with the trim at the limits, but if no power changes were made after the disconnect it should stay in whatever pitch it was at the time of disconnect, correct?

 

[surplus1]

Flyin2low,

I think I know where you're going with your #3 but I'm not quite ready (personally) to take that route - especially if your thinking is based on 'low time in type'.

From my perspective - if I were going at all to look at the 'experience' quotient, I would not be looking at time-in-type. The data we have so far do not appear, in my opinion, related to unfamiliarity with the specific type of aircraft.

Overall experience is a horse of a different color. I don't have any information on the overall experience of this flight crew.

I would add this thought:

"Experience is the exchange of the erros of youth for those of age." As it applies to pilots, a pilot may have 10K hours of 'experience' - or one hour of experience - repeated 10 thousand times.

Flying hours are a much too subjective measure of 'experience' for my gullet.

 

[Britpilot]

I understand everything you are saying here, except for this: are you saying the nose pitched up when AP disconnected or after they added full power?

I completely understand the nose up pitch change if they added full power after the disconnect with the trim at the limits, but if no power changes were made after the disconnect it should stay in whatever pitch it was at the time of disconnect, correct?

I think the point surplus1 was making was that the A/P would have trimmed more aft for the turn to intercept the LOC and that the stall occurred with this additional aft trim followed by power application and rapid pitch up moment then an accelerated stall while the airplane was in a bank.
In some aircraft the A/P will trim more than what is required for the given flight status, this is noticiable sometimes when you disconect the A/P to hand fly and you are given an airplane that is out of trim.

 

[surplus1]

Another idea on why it rolled left first:

What happens when you go from idle to full power in a propeller-driven airplane that doesn't have counter-rotating props?

You need to stomp down on the right rudder hard, or the airplane will be uncoordinated. Remember departure stalls when you didn't use enough right rudder? Which way did the stall break?

Points well made - in general true.

I'm not familiar with this aircraft type at all - haven't even seen one, other than in pictures.

That being said, I've been reading a lot about it since this accident occurred, and have learned a few basic things.

1. The propellers are quite large.
2. They are made by Dowty-Rotol.
3. The aircraft type has a history of propeller malfunctions that is way less than stellar.
4. A propeller malfunction, if not recognized correctly and handled correctly right away, can cause very severe controlability problems. It has happened more than once.

I don't know enough about the propeller control mechanism on this aircraft to be intelligent but there are generalities that are relevant.

A. In any propeller aircraft and especially one with such large propellers and so much available power - the torque factor you mention can be significant.

B. Most large propellers to not respond well to very large and abrupt power changes. I refer specifically to asymmetric 'spool up'. Very often, the two props (or the 4) do not respond equally (at the same time). Usually this is related to the particular governing mechanism. This can produce some control difficulties - although brief and transient in most cases.

C. A long time ago I was CA of another aircraft type (turbo prop) equipped with a Dowty-Rotol product. They may sue me, but the truth is that particular propeller was an accident looking for a place to happen. My pucker factor was orange for every hour in that thing. I know of at least one fatal accident (original Allegheny Airlines) on approach that was contributed to that propeller design. I know of another accident - I believe the only one ever in that different type - but equipped with essentially the same Dowty-Rotol propeller.

That was a long time ago (30 yrs +) and hopefull those anomalies have been corrected but it left a very bad taste - at least for me. Something akin to - Ill never buy another XXXX car. I have the same built in aversion to electrical systems by Lucas (the prince of darkness).

D. Much more recently I have flown another type that suffered from serious propeller control anomalies. That particular propeller caused at least 4 fatal accidents and its manufacturer fought tooth and nail to resist correcting the design flaw that was causal. Eventually they were forced (literally) to fix the problem.

We won't know until the NTSB is finished, but in this case I doubt that the props were a factor.

 

[atrdriver]

As I see it, the key to your statement is in the first sentence: "The part i dont get, is if there were no pitch control input changes prior to the AP disconnect, why would it pitch up?"

Actually there were lots of pitch input changes - all made by the auto pilot and unobserved by the crew. [If the darn airplane had a trim wheel they might have noticed it turning] Additionally, the autopilot was struggling to keep the wing from increasing the bank angle (due to the ice on that wing), which they also did not know.

The aircraft was in a descent - through 6000, 4000 to 2300. Power most likely retarded for the descent. Altitude is pre-selected to 2300.

As we reach 2300, altitude captures and is held by the autopilot. What happens now to airspeed? Unless power is added, airspeed will decrease.

If the autopilot was NOT engaged, and you didn't touch the yoke - what would happen to the nose as the airspeed decreases? It would drop off wouldn't it? If you did not want that to happen but you still wanted to slow down. what would you do? Trim nose up.

Now put the autopilot back in the equation. You told it to hold 2300 ft, and it does. As the airspeed decreases how does it do that? It trims the elevator nose up, to hold the altitude.

If you do nothing else it will continue to trim nose up and the airspeed will continue to decrease - until one of the two reaches the level required to hold that altitude with that amount of power. In other words, if the power available matches the power required to hold altitude at that speed, the auto pilot will stop triming and you will be in level flight with x amount of nose up trim and y amount of power - stable. If the power available/used remains less than required - airspeed will continue to deteriorate slowly until the auto pilot runs out of available trim capability or you exceed the critical AOA and stall.

I am only saying how it works - not what they did. I assume that they added enough power to hold the desired speed (or what they thought would hold it).

Everything is now stable and the auto pilot has stopped triming nose up -but - it has NOT removed much if any of the trim previously input. You're still at 2300 ft and headed for the localizer. Glide slope is not alive and has not captured.

As you approach the localizer the autopilot begins a turn to capture it. The auto pilot is still flying. What happens now?

As the bank increases more back pressure is required to hold the altitude. The auto pilot provides in by additional nose-up elevator trim. Something else also happens - the airspeed begins to deteriorate (slow) again. You decide to accept the slightly lower airspeed and you don't add more power - it's already where you think you want it.

Meanwhile bank angle is increasing and elevator is trimming nose-up (slowly). Bank angle tries to increase beyond 25 deg. (due to the ice) until the auto pilot exceeds its limit and kicks off. The nose pitches up and the wing stalls.

Instantly the bank increases from 25 to 45 degrees - further increasing the stall speed. What happens to stall speed as bank angle increases? Yep, its higher than in was before. It was already on the edge - you just didn't know it.

Just as you act to correct the bank the wing stalls. You call for full power and all that up elevator trim is still there. Where does the nose go before you can stop it? All the way to +31 degrees nose up and you have the yoke full forward. There's a lot of power there and some very big props.

Down goes the nose - very rapidly. Your control input has taken effect There is still too much elevator trim for that amount of power and you're pushing hard.

The instant you see 45 degrees nose down you reverse the pressure and pull like hell. You still have almost full aileron cranked in to pick up the left wing. You havent thought at all about trim. Who would?

Just as you apply that back pressure you now enter an accelerated secondary stall. The aircraft snaps to the right - exceeding the vertical bank angle. It is completely out of control - plus you just lost a thousand feet.

The rest ...............

It's all hypothetical ... just a theory.

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

 

[q100]

Points well made - in general true.

I'm not familiar with this aircraft type at all - haven't even seen one, other than in pictures.

That being said, I've been reading a lot about it since this accident occurred, and have learned a few basic things.

1. The propellers are quite large.
2. They are made by Dowty-Rotol.
3. The aircraft type has a history of propeller malfunctions that is way less than stellar.
4. A propeller malfunction, if not recognized correctly and handled correctly right away, can cause very severe controlability problems. It has happened more than once.

I don't know enough about the propeller control mechanism on this aircraft to be intelligent but there are generalities that are relevant.


D. Much more recently I have flown another type that suffered from serious propeller control anomalies. That particular propeller caused at least 4 fatal accidents and its manufacturer fought tooth and nail to resist correcting the design flaw that was causal. Eventually they were forced (literally) to fix the problem.

We won't know until the NTSB is finished, but in this case I doubt that the props were a factor.

I agree with the last thing you said...

Dash8s do not have, at least not that I know of, a "less than stellar" history of prop problems. Not to say they've not happened, but they are rare and usually MX (and pilot) related. I know of at least one crew that took off with faulty torque indications, and, guess what, had an unscheduled autofeather on T/O, for example...

I believe the type you refer to in "D" was the Brasilia? Weren't they Hamilton Standard props that were shedding blades? At least one of those events was traced to MX.

Too many people, even Jim Hall (ex-NTSB chair who really oughta both a) know better than to think one accident, due to causes yet unknown, in an a/c type with no history of similar incidents is cause for grounding the fleet, and b) keep his yap shut) are in too much a rush to pin the blame for this crash on someone or something. How about we all wait for the facts?

Speculating is one thing - we all do it and it can produce some useful results. Rushing to judgement is another beast entirely, and it does no one any good while potentially damaging the innocent.