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Continental TurboProp crash inbound for Buffalo

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Continental TurboProp crash inbound for Buffalo

Old 15th Feb 2009, 17:42
  #281 (permalink)  
 
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Small Question:
When you say after Autopilot Disengage...it leaves the pilot with an "out of trim" Aircraft...Wouldn't the trim stay in place...but you just hand fly it...
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Old 15th Feb 2009, 17:50
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Would a tailplane stall, followed by a wing stall, account for turning the aircraft almost 180 degrees around the vertical axis, in 1600 vertical feet of space?

No speculation, just a question to those who would know.
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Old 15th Feb 2009, 17:57
  #283 (permalink)  
 
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Yes Conan.

The Stick Pusher System, Stick Shaker System and the flap auto pitch trim system.

The Stall protection system consists of 2 SPMs or Stall Protection Modules and uses the following parameters to calculate when the a/c is near a stall condition:

AoA data
Flap Position
EAS
Engine Torque
Icing Status

Both SPMs are used to calculate the Stick Pusher operating angle using the following parameters:

AoA
Flap Position
EAS
Power Lever Angle
Condition Lever Angle
Icing Status.

The SPMs calculate when to operate the Shaker & Pusher systems and sends a signal to the Automatic Flight Control System to disengage the autopilot, also for Stick Pusher activation it uses an average of the 2 AoA vane inputs.

Stick pusher operates under these conditions

CAS is less than 215kts
Altitude is +200ft AGL
Stick Pusher shutoff annunciator switch is not in the off position.
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Old 15th Feb 2009, 18:00
  #284 (permalink)  
 
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I recognize this entire thread is mostly speculation, and the majority of "posters" are professionals who recognize the need to wait for the NTSB's official findings. That said, I also think this line of discussion has opened the eyes of many pilots to the inherent danger of flight into icing conditions and the limited amount of knowledge regarding tail plane icing/stalls. If anything will or has come of this disaster already it's everyone's increased awareness of the dangers of manned flight and hopefully that heightened awareness will lead to even safer skies.

The last few posts have started my mind churning on the idea/concept of a tail plane stall/main wing stall "coffin corner" of sorts. A position where the aircraft is iced increasing the stall speed of the main wing, drag, and thusly the power setting to maintain the suggested increased airspeed. Of which increased power settings can apparently contribute to a tail plane stall. A change in configuration, namely flaps, could potentially exacerbate this situation. I bring this up not to suggest it occurred in this situation, but seek the experience of a larger audience as I could not find anything connecting the overall effects of main wing ice and tail plane ice. The corrective action for both types of stalls are somewhat counter to each other and there seems to be little information on when these two potentially disastrous situations cross, if they do at all. I can only hope more research will be done to ensure we are doing all we can to make the safest form of transport safer.


Not sure if it's been posted yet, but an interesting AC regarding tailplane icing.
http://rgl.faa.gov/REGULATORY_AND_GUIDANCE_LIBRARY/RGADVISORYCIRCULAR.NSF/0/b178d8b350e1cc3a86256b6e004fcd3f/$FILE/AC23.143-1.pdf

Last edited by oshksh; 15th Feb 2009 at 19:11.
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Old 15th Feb 2009, 18:28
  #285 (permalink)  
 
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Autopilot ON

AP is reporting:
Chealander says the preliminary investigation indicates the autopilot was still on when the plane crashed.
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Old 15th Feb 2009, 18:29
  #286 (permalink)  
 
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NTSB says auto-pilot was engaged when plane went down in icy conditions...

Last edited by nippysweetie; 15th Feb 2009 at 18:33. Reason: NTSB typo
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Old 15th Feb 2009, 18:32
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Steve Chealander of the NTSB confirms Colgan Air recommends pilots fly manually in icy conditions and must fly manually in severe ice.
Pilot reported "significant" ice on wings and windshield just before crashing.
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Old 15th Feb 2009, 18:39
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I flew the Q400 as well as the 200 and 300, and was always told that we select the boots on as soon as we detect icing. Some people used to mention the bridging theory and that you should wait for ice to build up, but the reponse was always: "That's what the dwell time is for."

So I was always told that the bridging theory, whether or not it is possible on other types (and the evidence appears to be that is it not, or at least no factor), it is not relevent for the Dash de-icing system.
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Old 15th Feb 2009, 18:45
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oshksh

If anything will or has come of this disaster already it's everyone's increased awareness of the dangers of manned flight and hopefully that heightened awareness will lead to even safer skies.
Yes, that's the fortunate OR unfortunate thing about all aircraft accidents. Pilots become very conscious for the next few days/weeks/months, and then are likely to not think about it as much. I'd bet anything, pilots were looking for places to "land" after take-off following the Hudson River thing. Probably still are, but soon other things will take priority. Same with the icing; everyone will be overly conscious about it until Summer. Sad but true. Nature of the beast.
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Old 15th Feb 2009, 18:46
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Oshksh, add to your possible tailplane/main wing stall "coffin corner", a stick pusher operating with it's own set of rules and an autopilot which either may have been engaged at time of impact, or engaged just prior to the stick pusher disengaging it.
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Old 15th Feb 2009, 18:46
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Thanks Deano.

I ask because it has so far been reported that whatever happened, started "immediately after" flaps 15 was selected. Wether this "immediately after" means right after the handle was moved, or after the flaps had moved is not clear.

If it was at flap handle movement the pitch ocsillations started, then it starts to point at something entirely different, than what has been speculated on so far.

If, as reported, the AP was engaged at impact and both stick shaker and pusher was active, then a technical malfunction becomes more of a possibilty.
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Old 15th Feb 2009, 19:03
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NTSB says auto-pilot was engaged when plane went down in icy conditions...
An earlier report on the Wall Street Journal web site indicated that the autopilot was disengaged as the aircraft was configured, now the WSJ echoes this AP report that the A/P was on.

Hopefully we'll get more at this afternoon's briefing.
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Old 15th Feb 2009, 19:09
  #293 (permalink)  
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Deano, my recollection of the Dash is that the autopilot disengages when the stick shaker is activated. It appears you are more current on the Dash than I am. Can you confirm or deny if that is the case?
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Old 15th Feb 2009, 19:18
  #294 (permalink)  
 
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As SLF regularly using turboprops to / from GCI, I have been in situations where the passengers / cabin crew have alerted the flight deck when ice has been building up on the wings (resulting in a quick drop in altitude) and a (longer) windy approach to GCI. I would guess however that if ice is forming on the visable wings, it's also on the tail. Given that the ATR's/ Q400's on local sectors like LGW-GCI are in ice forming conditions for a longer % of their flight, is it time to access the potential risk for these flights as oppossed to longer flights, and set some min /max values in keeping with current local conditions?
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Old 15th Feb 2009, 19:32
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Status of Q400

Unless pilot error, sabotage or criminal act isn't declared as cause very soon, I imagine this is not good news for all current Dash 8 Q-400 operators and for Bombardier's future orders.
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Old 15th Feb 2009, 19:47
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Anyone like to explain why turboprops like the Q400 dont have hot bleed air deicing? Rubber boot systems by their nature are less efficient and more prone to wear. In my TP days I often remember seeing patched boots.......

I cant think of any good reason apart from cost....

Lets face it the DHC8 is not the sort of aeroplane either a passenger or a pilot choses to fly given ay choice. Bashing about low level in the wx with vibration and noise may be fine for bottom fishers like FLYBE's accountants but it really is a pretty unpleasant aeroplane all round.
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Old 15th Feb 2009, 19:50
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The automatic ice detection system will warn the flight deck well before any pax would notice. I can honestly say in all my time on the dash 8 , NO passenger or CC have notified us of icing on the wings!

As to the future of the Dash 8, if the icing systems are used correctly and the correct procedures in the AOM are followed there is not a problem with it.

Pure speculation as to how a system works or what caused a crash where people have been injured or killed, is nothing but counter productive. Have some patience and allow the official report to be delivered. and if you want to know how the Dash 8 systems actually work rather than guess, contact Bombardier and buy the F"%ing manuals!
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Old 15th Feb 2009, 20:03
  #298 (permalink)  
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I cant think of any good reason apart from cost....
This is totally irrelevant but how about a common type rating?
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Old 15th Feb 2009, 20:03
  #299 (permalink)  
 
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Chesty

Yes mate this is the case, the SPMs sends a signal to the AFCS to disengage the AP on stick shake activation.

MVE is spot on, it's a concerning time for us Q4 drivers as to whether there's any potential issues with our birds in icing. This is a very healthy debate, and I personally have learned loads just reading these pages, but speculating about type issues is doing nobody any good. Let's wait for the NTSB findings.

D777
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Old 15th Feb 2009, 20:17
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Cheers Deano, it's amazing how quickly you forget stuff like that.

So according to the NTSB latest

Chealander says the preliminary investigation indicates the autopilot was still on when the plane crashed.
If the A/P was still engaged then it would appear that the stick shaker and pusher haven't activated. Unless there was a problem with these systems this would indicate that the aircraft never stalled. Curiouser and curiouser.
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