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Continental TurboProp crash inbound for Buffalo

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Continental TurboProp crash inbound for Buffalo

Old 15th Feb 2009, 13:37
  #261 (permalink)  
 
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Why is everyone so fixated on tailplane stall? The facts don't support it.

Most of the information from TV is ridiculous and misleading. The latest report from the NTSB said the Stick Shaker and Stick Pusher were activated. That doesn't happen with a tailplane stall.

The NTSB said it impacted in a flat attitude. That doesn't happen with a tailplane stall either. The NTSB has never mentioned tailplane stall. So where is it coming from?

You guys would all make very poor accident investigators. Why not stick to the facts for a change.
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Old 15th Feb 2009, 13:42
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Secondary stall maybe.

We donīt know when exacly the stick shaker and the stick pusher where activated. At 2220 ft or short prior impact.

Maybe they flew out of the tail stall. But with Ice on the wings they pulled to long, or too hard. You cannot tell without the real flightdata.

Inbalance
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Old 15th Feb 2009, 13:44
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So, NASA is wrong and Q400 autopilot is an exception? Or am I missing something here?
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Old 15th Feb 2009, 14:02
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Some Prior Research into Asymmetric Icing due to Same Direction Prop Rotation

Considering prop rotational directions and the resulting asymmetry of lift and drag due to icing buildup under helical prop slipstream influence (an Academic Study with DHC8-400 graphics)

LINK ...(to an explanation for asymmetric icing and the possibility of asymmetry-generated autorotation)

.

.
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Old 15th Feb 2009, 14:25
  #265 (permalink)  
 
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So, NASA is wrong and Q400 autopilot is an exception? Or am I missing something here?
No im not saying that, im saying as a Q400 driver ive never been trained or seen in SOP's that the autopilot cannot be engaged in icing conditions.

I think that NASA video is very good, and have my own opinons on what might have lined up all the holes in the cheese to cause this crash, but im not an accident investigator unlike many other PPruners, im just giving the answers to the question you asked.
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Old 15th Feb 2009, 14:35
  #266 (permalink)  
 
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Im not 100% sure but isnt the stick pusher activated when the AoA vane reaches a certain limit? A therefore with a Tail plane stall your AoA vane wont be at a critical AoA a therefore wont activate?
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Old 15th Feb 2009, 14:55
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That video was very very interesting thank you for sharing it. I flew a high T-tail for over 2 years and I honestly got a shiver down my spin thinking about the recovery tehnique I would have adopted and what the guys/gals from Nasa are saying. One thing I would like to add and in no way am I linking this to the recent incident and please correct me if I am wrong but certainly on the a/c I flew it was very important to allow an acceptable build up of ice on the wings Before using the boots? If you didn't them you could actually render them useless......just a point.
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Old 15th Feb 2009, 14:56
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Originally Posted by inbalance
Secondary stall maybe.

We donīt know when exactly the stick shaker and the stick pusher where activated. At 2220 ft or short prior impact.

Maybe they flew out of the tail stall. But with Ice on the wings they pulled to long, or too hard. You cannot tell without the real flightdata.

Inbalance
I don't think they had a tail plane stall, recovered, experienced a secondary stall, and then crashed in a flat attitude. There just wasn't enough time and altitude to do all that.

The aircraft was in a descent and had just leveled off at 2300 ASL. That is less than 1600 above the ground.

That is a fact.

The aircraft crashed in a flat attitude.

That is a fact.

The stick shaker and the stick pusher where activated.

That is a fact.

Now for some speculation....

They may have been preoccupied with the icing and did not increase the power when they leveled off at 2300'. They may have experienced some type of pre stall warning. Because they were preoccupied with potential tail stall, they may have instinctively applied a tail stall recovery when there was no tail stall. This would explain the retraction of the gear and flaps.

Last edited by Lost in Saigon; 15th Feb 2009 at 15:06.
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Old 15th Feb 2009, 15:20
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Again,

Enough already of the hypothesising!

The Q400 has a fully hydraulic tail, unlike virtually any other turboprop. The Elevator feel is synthetic, not real, so you won't get any sensation from aerodynamic problems, hence leaving in the autopilot. it is certainly not like the old dash model, but the layout and way of operation is similar enough for that common type rating. A lot of the commonality fitted to the Q400 is what gives problems in operation.

Also the stick push is disabled at really low altitudes for the obvious reasons......

The true facts of what happened are the traces on the FDR from the AHARS and ADCs. They'll hopefully have data on the PFD and MFD displays, switch position for all switches, etc, etc. Let the NTSB piece it all together from THESE FACTS, not the Mish mash of stuff thrown up here.

The implications of what happened are too important to throw about and wave at outsiders like happens on this site.
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Old 15th Feb 2009, 15:22
  #270 (permalink)  
 
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I need some help here (too many competing opinions)

from above

The aircraft was in a descent and had just leveled off at 2300 ASL. That is less than 1600 above the ground.

That is a fact.

The aircraft crashed in a flat attitude.

That is a fact.

The stick shaker and the stick pusher where activated.

That is a fact.
I now add the NASA video as some reasoning (I'm not calling it a fact yet because for all I know it may not apply to this accident)

I also am considering as fact the earlier comment about the DFDR where severe pitching and rolling were experienced (no idea yet if this was before or after stick shaker)

From the NASA video lesson I tend to associate the severe pitch oscillations after flap down selection with Tailstall and not with the onset of wing stall (stick shaker).

So I'm left with the possibility of one leading to the other.

However it seems to me that in order to get stick shaker as a secondary that you need a abnormally low speed or a significant forced pitch up.

Now I suspect that I probably have something wrong in my reasoning so please correct what I have wrong
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Old 15th Feb 2009, 15:24
  #271 (permalink)  
 
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I found this submission on another forum, and I like to see whether it has any legs, in light of what we now know to be fact.

From a contributor with the handle of "Normy", on Continental Flight 3407 crashes in Buffalo, 44 aboard - Pelican Parts Technical BBS

What happened in this one? I don't know. The Dash-8 I flew had vastly weaker engines than the Q400 involved in this accident. I will tell you that this is a VERY easy to fly plane- the only thing about the Dash-8 that I could possibly criticize is that the rudder is extremely sensitive; any time you moved the throttles, you had to bump the rudder trim. And you didn't touch the rudder pedals with your feet; you THOUGHT about coordinating with the ailerons and your THOUGHT was enough rudder pressure [feet on the floor..] to keep the ball in the center!
Could a rudder problem lead to an accident like this?
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Old 15th Feb 2009, 15:26
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Don't know 'bout "T-Tail" machines, but you can get a tail stall (indication anyway) LONG before any stick shaker. At least in a B-737-200.
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Old 15th Feb 2009, 15:30
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This may have been said before, sorry, but I have not read every page. This accident sounds very similiar to an Atlantic Coast Airlines J41 in CMH back in the early 90's. The crew was concerned with the icing conditions, upon level off, the crew never pushed the power up, stalled and crashed on approach. Not saying this is what happened, just sounds similiar.
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Old 15th Feb 2009, 16:09
  #274 (permalink)  
 
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Aircraft after the crash were reporting icing conditions above 2300 feet but shedding the ice below 2300 feet. If they were performing the tailplane stall recovery at 2300 feet and the ice shed descending to the ground now they would be in a very high sink rate situation with full elevator authority to reduce the pitch but activate the stick shaker and pusher because of the aoa as the flaps were coming up.
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Old 15th Feb 2009, 17:01
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DC-ATE

Don't know 'bout "T-Tail" machines, but you can get a tail stall (indication anyway) LONG before any stick shaker. At least in a B-737-200.
Just curious: What kind of indication you get on a B732?
Thanks,
A
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Old 15th Feb 2009, 17:09
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Just curious: What kind of indication you get on a B732?
Thanks,
The yoke just started oscillating about 15 kts ABOVE when the stick shaker came on. I've related the experience on here someplace, don't know what thread it's in any more.
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Old 15th Feb 2009, 17:17
  #277 (permalink)  
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I'm inclined to think that there was a tail stall, with the correct action taken in good time. But it's beginning to look like this was followed by an immediate entry into a deep stall.

If this was the case, I can sympathize completely with the PF, in as much that the available time to recognize an entirely different condition, let alone act on it, was lamentably far too short.
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Old 15th Feb 2009, 17:23
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Loose rivets

Or there was an onset to a normal wing stall due to wing icing, but the crew felt it could be a tail stall and took the appropriate action (reduce power,, pull the nose up) worsening the stall to becoming a deep stall.

After all the crew had not so long ago converted to the 400, so perhaps they were too focussed on tail stalls?
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Old 15th Feb 2009, 17:36
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Are there any systems on the Q400, besides flaps, that recieve flap handle position inputs?
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Old 15th Feb 2009, 17:38
  #280 (permalink)  
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I'm quite taken-aback about the vast differences in the newer aircraft. I'm sure the company gave substantial retraining, but it really does put a burden on the crew for the first couple of hundred hours.


Just a point I'd like to make...it's kind of germane in terms of the psychology.

I came back to a twin turbo-prop for a 'retirement job'. It was taking a while to settle in, and one really dirty night going into Belfast City airport, everything was bouncing around and then the stick-shake went off. I reacted instantly, but the darn thing kept rattling away. Even when I'd cross-checked with the starboard and standby instruments, that noise and feel in the controls was desperately hard to ignore. For 40 years, it had been a total requirement to react.

Imagine now, two opposing sets of disorienting symptoms, all within a few seconds. A very tough situation to be in.
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