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Continental TurboProp crash inbound for Buffalo

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Continental TurboProp crash inbound for Buffalo

Old 27th Mar 2009, 04:59
  #921 (permalink)  
 
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The stick shaker is a stall warning device, not a tail stall warning device. Perhaps the instructional videos ought to emphasize the fact, if they don't already.
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Old 27th Mar 2009, 05:23
  #922 (permalink)  
 
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tail stall

The first thing I thought when hearing of the Colgan accident was tail stall in icing,especially since early reports had it the stall occurred just at flap extension. In fact, I immediately sent my company a Youtube video on tail stall and recommended it be sent to our pilots as a refresher. I fly a Caravan, a notoriously bad ice carrier.
We have specific icing DVD courses each year, but they hardly stress tail stall, which requires a pull back, not a push, and often happens at flap extension. Same tendency in the Jetstream 32.

The Colgan captain, although with low time in type, was certainly not inexperienced, as some here have alleged. The Q400 is fairly new to the company, with more deliveries planned. I understand Colgan hired some direct entry captains (a rare thing in the US) specifically to ensure they had experienced skippers in the Q400, the largest type they operate, as it enters the fleet.

There was little time and height to react, and if the crew had just entered icing conditions, they may indeed have perceived they encountered a tail stall.

Second guessing is easy. Reacting correctly instantaneously in a situation which might not be what it first seems is not.
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Old 27th Mar 2009, 06:17
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Differences being, the horizontal stab AOA is suddenly and significantly increased with flap extension, and would be likely to stall before any stall warning device in the aircraft were to activate, since these devices measure main wing AOA, which would be DECREASED with flap extension..the video, while enlightening, also mentions increasing power exacerbates the tail stall...on a conventionally configured tailplane aircraft..no mention of effect or lack of on a T-tail model...a THS..trimmable horizontal stab configuration minimizes the possibility for a contamination-induced stall, as it is "trimmed" into the relative wind...only turboprop I ever flew with this configuration was the Metroliner...

Threat: Tailplane icing..loss of control..failure to differentiate between stab, or mainwing contamination aircraft reactions.

Additive factors: Organizational anomaly..regulators, manufacturers, operators failure to address and provide timely information, and procedures to address this hazard..

the above is no condemnation of the crew's reaction to the situation..merely an observation that the necessary information was not available to allow the crew to respond properly..

Last edited by ironbutt57; 27th Mar 2009 at 06:28.
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Old 27th Mar 2009, 06:44
  #924 (permalink)  
 
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According to one line of reasoning I saw somewhere, probably here, the Colgan pilot may have mistaken the stick pusher for a phenomenon that can occur during a tail stall in which aerodynamic forces act on the elevator to pull it downward, pushing the yoke down with it. If the pilot was familiar with this phenomenon, he might have thought the stick being forced forward was being caused by a a tail stall.
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Old 27th Mar 2009, 06:57
  #925 (permalink)  
 
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We have built simulator models and introduced upset recovery training, as aircraft upsets have surpassed CFIT as a major cause of hull-loss accidents, now it may be time to introduce comprehensive aircraft specific simulator training programs to train pilot recognition of, and develope and address the differences in recovery procedures between tailplane, and wing contamination upsets...face it turboprops will never disappear as once thought, and the threat remains very real...so lets not make this tragedy yet another waste of lost lives...
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Old 27th Mar 2009, 09:41
  #926 (permalink)  
 
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whoever pulled back on the controls either had lightning quick reflexes
There is no evidance someone pulled back on the controls, the FDR cannot distinguish between a human hand pulling the stick back, or the aerodynamic forces themselves moving the control column.

The more logical reason for the "lightening quick" pull back is because as the stick shaker activates the autopilot is automatically disconnected.
And as said by me and others, the autopilot would have trimmed right back, almost full aft to maintain the altitude while the speed was decaying, the autopilot then disconnects and the control column moves full back due to the trim forces and the aircraft pitched up.

It is unfortunate that commuters with their low pay and benefits need to accept underqualified people to fill these positions


Its a unfortunate that people like you with the attitudes, views and complete lack of understanding get a flying job in the first place!
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Old 27th Mar 2009, 09:46
  #927 (permalink)  
 
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A rare thing...

Someone confessing ignorance here on R&N, so enjoy it...

You know, I really don't know anything much about this "tail stall" phenomenon. (Well, same as I am waiting to hear just which t-tail jet it is that needs the nose pushed down to recover from a full-breaking stall yet is certified without a stick-pusher, really!)

Where can I find an authoritative account of exactly what a "tail stall" is, please? I think I know what is under discussion but I never saw it exactly, officially defined.

I take this to be an ice-contaminated tail stalling well before the wing reaches the critical AOA (Angle Of Attack) perhaps due to the change in airflow direction from flap extension. The Twin Otter, for instance, has a prohibition on using more than Flap 10 when icing has been encountered, which must be for this reason but you cannot see the term "tail stall" itself used in the aircraft manual or checklist.

I can see the logic in commanding a pitch-up and/or removing flap, when the tail AOA would decrease for recovery from its stalled condition, when these are both actions that would be contra-indicated for a normal stall.

The funny thing is, I do hold a current FAA Flight Instructor Airplane Single and Multiengine; Instrument Airplane Gold Seal licence but there are still areas of personal ignorance I come across now and then, hence this question.

FTC, above... Hope I come up to your demanding professional standards, probably not but here goes anyway:

I would have thought that autopilot disconnect would see the aircraft trimmed to stay at the speed for the last attitude that the autopilot had commanded while holding altitude, assuming here that it was in "Altitude" mode. That is the way an autopilot system works: it senses a pitch control force and tells the trimmer to run until the force is gone so that its servo is not continuously activated.

Say you want to hold 3 thousand feet, when you then reduce power. You should see the speed decay while the autopilot holds altitude and the trimmer runs "nose up." When you get to the stall regime the autopilot will kick off, giving you a warning tone but when it disconnects you shouldn't get the airplane doing a sudden pitch-up; it should just sit there properly trimmed if you still have enough power to sustain level flight or else exhibit a nose-down pitch if the speed is decaying, since pitch trim is really trimming to a speed and not an attitude.

Given all of that then where should this sudden nose-up input come from except from the crew manipulating the controls?

Last edited by chuks; 27th Mar 2009 at 10:02.
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Old 27th Mar 2009, 10:27
  #928 (permalink)  
 
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pilots often take a ''winter'' written exam to make sure they know the dangers of winter flying.

wouldn't it be odd if the pilots had just taken the exam and had a number of questions on tail stall...their minds might be primed for such a problem.

I want the NTSB to release life training records on both pilots including winter exams .

I also want to know. point blank, if the airline and the manufacturer sent data to the pilots in quesation that the Q400 doesn't tail stall.
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Old 27th Mar 2009, 11:13
  #929 (permalink)  
 
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Chuks, I dont know where you find me demanding "high professional standards", maybe you should read through my posts again to make sure your not seeing things....

Through experiance on type, the DHC8 Autopilot does not give the aircraft back to you fully trimed, during normal Ops this generally means on finals you get a 3-4 degree pitch up when you disconnect in the normal landing config.

Ive never had the experiance of disconnecting the autopilot in the config/speed the buffalo a/c was in and hope I will never have to, so its just speculation on my part, however with speed and aerodynamic flow constantly changing in a stall I dont fully agree with your theory that the aircraft would be 'trimmed' and maintain the pitch. Also the Rudder trim is completly manual, so if the pilots were distracted and not flying the plane the rudder would no doubt be completly out of trim as the DHC8 is very sensitive on the rudder (that I have experiance of).

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Old 27th Mar 2009, 12:19
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Protectthehornet

I also want to know. point blank, if the airline and the manufacturer sent data to the pilots in quesation that the Q400 doesn't tail stall.
Sound question - but from where you do get the assertion that the Q400 doesn't tail-stall? It seems to me, from my elementary aerodynamics, that all ac could tail-stall if iced enough?

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Old 27th Mar 2009, 13:32
  #931 (permalink)  
 
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chucks et al, Tailplane stall.
The extract is from a BAE SYSTEMS safety awareness magazine. Note that the initial icing section applies to both jets and turboprops, but only the turboprops have specific advice for tailplane stall recovery.
This might imply that in theory, all types could be susceptible to tailplane stalling, but in practice, only the turboprops have encountered the problem – and fixes (restrictive flap use) were put in place.
Most jet aircraft have powered (irreversible) controls which negate the problem, but note that the BAE 146 / RJ have manual controls:
– IIRC the Q400 has a powered elevator and thus may not be susceptible to tailplane stalling.
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Old 27th Mar 2009, 14:05
  #932 (permalink)  
 
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I can understand why a powered elevator might preclude control "snatching" but educate me please on how they would prevent the horizontal stab from exceeding it's critical angle of attack..which would be changed in the event of contamination.....

Last edited by ironbutt57; 27th Mar 2009 at 16:20.
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Old 27th Mar 2009, 14:54
  #933 (permalink)  
 
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Yes, please tell.
Thanks
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Old 27th Mar 2009, 15:17
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Once more, NTSB´s exact words:

when the stick shaker activated, there was a 25-pound pull force on the control column
That to me sounds like someone was pulling the column, even though they don´t really say so, for whatever reason. Notice they say "when" instead of "after".
I suppose we will only find out more during the public hearing, which unfortunately is another 6 weeks away.
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Old 27th Mar 2009, 18:06
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have you ever?

Have you ever been flying along, hit turbulence and pulled the yoke to regain the sense of negative G?

just wondering.
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Old 27th Mar 2009, 18:27
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Originally Posted by Finn47
That to me sounds like someone was pulling the column
Agreed. There is no other way to interpret this.

If the A/P or trim was holding full nose up trim, when the A/P disconnected, you would not describe it as a:

"a 25-pound pull force on the control column"
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Old 27th Mar 2009, 18:36
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Originally Posted by alf
– IIRC the Q400 has a powered elevator and thus may not be susceptible to tailplane stalling.
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Old 27th Mar 2009, 18:53
  #938 (permalink)  
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Have you ever been flying along, hit turbulence and pulled the yoke to regain the sense of negative G?
Well.... No.

The certification standards I have to test to say:

A pull must be required to obtain and maintain speeds below the specified trim speed

When I pull, I really expect to experience a reduction in speed, and an associated increase in positive "G".

Pilot DAR


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Old 27th Mar 2009, 19:29
  #939 (permalink)  
 
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No Airspeed Indication?

the above is no condemnation of the crew's reaction to the situation..merely an observation that the necessary information was not available to allow the crew to respond properly..


I guess most transport type aircraft don't have an AoA gauge, but no airspeed indication? That should have been all they needed to warn of an impending stall.
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Old 27th Mar 2009, 20:09
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Alpha is forbidden information!

The FAA will not approve the direct display of AoA (Angle of Attack, also referred to as Alpha or designated so with the Greek letter "alpha").

You may see a little AoA indicator on an FAA-certified aircraft but it will omöbe captioned "Fast" or "Slow" and/or colour-coded Green or Red when Fast/Green means lesser Alpha values and Slow/Red means higher Alpha values.

I asked an FSI instructor why this was so, when we were flying a Citation with a little display stuck up there atop the glareshield, close to your eye-line when you were looking out at the runway on approach (which is why it was placed there, I assume).

He told me that the FAA just do not want civvy pilots having that information, even though Navy pilots use it all the time. Someone else here may well have more knowledge of this, when I stand to be corrected but that is what I was told.
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