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Q400 ADC or SPS Failure?
Speculation:
Possible contributing factor - Air Data Computer failure. or Stall Protection System failure I don't believe any pilot with proper indications would intentionally pitch to 31 ANU to recover from a stall. To override the pusher and reach 31 ANU, one would think the aircraft had more momentum (speed) than shaker/pusher (AOA) conditions. ... |
Assuming the glass in the Q400 is similar to other airplanes...
An ADC failure on one side should have triggered a comparator message...that should have given the crew time to figure out which was the good side. Although that could get pretty confusing in a busy phase of flight. For very obvious reasons SPS will NOT trigger unless BOTH sides of the air data system agree. You would need dual failures, both producing identical data indicating a stall, but without setting a failure bit...the odds are astronomical against this. |
Originally Posted by rickair7777
(Post 561676)
For very obvious reasons SPS will NOT trigger unless BOTH sides of the air data system agree. You would need dual failures, both producing identical data indicating a stall, but without setting a failure bit...the odds are astronomical against this. Probably better to say it SHOULD NOT than it WILL NOT. Stranger things have happened. ever watch Fate is the Hunter? |
Originally Posted by SmoothOnTop
(Post 561636)
Speculation:
I don't believe any pilot with proper indications would intentionally pitch to 31 ANU to recover from a stall. ... Not faulting the crew, but if you're in the comfy world of flying an approach and suddenly the pusher goes off and throws the yolk forward, what would be your first instinct? Most likely to pull back and protect altitude. Its also what airlines train for. Most airlines don't have you lose altitude in a stall situation, they want you to maintain altitude and use power and proper pitch to accelerate. See a problem with flying how you train? |
Fly the airplane first. Back to day one of flight training, listen to what your rear-end is saying (when your instruments are no good to you, of course)...and DAL has a very good point -- they expect you in the sim to hold altitude above all else, picking up the airspeed in the recovery. Also, the only time we ever see the pusher is if the approach to stall goes bad; we never actually see exactly how the aircraft behaves.
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Well, perhaps the crew recognized the tail stall and had to fight against the stick shaker. This could have triggered the oscillation and aggravated the tail stall further (if indeed this is the ultimate cause). Just my .02.
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any stall is to be recovered according to 99% of any 121 procedure by maintaining the altitude as best as possible and using power to muscle out of the condition. with extra ice both on the airframe, props and wings the extra drag along with the resultant decrease in performance I wonder how the recovery will actually work. I also highly doubt that any flight crew would let the airspeed get that dangerously slow in those conditions.
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Originally Posted by DAL4EVER
(Post 561838)
Most airlines don't have you lose altitude in a stall situation, they want you to maintain altitude and use power and proper pitch to accelerate. See a problem with flying how you train?
Even today with my 121 PC checks, we do 3 diferent stalls and all require holding altitude, which we all know means we have to pitch back a lot to maintain as we lose airspeed. My first reaction with a stick pusher would probably be to pull back. Your first thoughts would most likely be "why is the plane diving me into the ground, I need to hold altitude." |
Originally Posted by Killer51883
(Post 561931)
I also highly doubt that any flight crew would let the airspeed get that dangerously slow in those conditions.
The Wall Street Journal is reporting that a fundamental pilot mistake -- what to do in a stall -- and not icing may have triggered the fatal dive of the Continental Connection plane that crashed near Buffalo, killing 49 on board and one in the house it hit. Citing sources who have thoroughly examined information from the plane's flight data recorder, the paper said the commuter plane was flying at an unsafe speed as it approached the airport, and experienced an automatic stall warning. 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. Still speculation of course. This crew was new to the airplane and probably did not have much time in airplanes with a vertical tape airspeed display. This could have lead to a loss of situational awareness. The crew was slowing and configuring the airplane and did not notice just how slow they were going until it was too late. I could see the captain pulling hard on the yoke in response the the pusher - especially since the stall caught them by surprise. |
Getting carried away
I think we are getting carried away with trying to investigate this accident in an information vacuum. While I initially suspected an ICTS event, because the upset began as flaps were selected and the aircraft was reported to have crashed in an extreme nose down attitude, I now must say I do not know. I could speculate but it would be pointless so I won't. I do have ideas that I will keep to myself. But to see all the theories floating around disturbs me. We speculated on here about tail stalls and then the media asked about tail stalls. I think we need to quit giving the media and the lawyers ammunition with which to attack these pilots and our industry.
Lets quit specualting publicly and let the NTSB do its job. |
Respectful speculation can be educational.
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While we have all be enlightened in the last couple days about tailplane icing/stall we need to put that subject to rest. Tailplane stalls do not activate the shaker and certainly do not create a rapid pitch up. This accident does not involve tailplane icing/stall
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Originally Posted by ExperimentalAB
(Post 562123)
Respectful speculation can be educational.
As long as we stay mature, professional, and respectful I can't see any reason why speculation couldn't lead to a better understanding for us as flight crews. |
Originally Posted by ExperimentalAB
(Post 562123)
Respectful speculation can be educational.
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All great points.
Just to clarify the difference between shaker and pusher...
Originally Posted by DAL4EVER
(Post 561838)
I've seen countless pilots fight the pusher when activated and you in essence create an extreme PIO with pitch attitudes ranging from plus 40 to minus 30.
Doesn't this generally happen when a crew, recovering from stick shaker has added full power/thrust and pitched up too aggressively thus begining the PIO cycle you describe? I guess the machine still had enough tail authority to rotate to 31 ANU after pusher activation. ..if you're in the comfy world of flying an approach and suddenly the pusher goes off and throws the yolk forward, what would be your first instinct? Most likely to pull back and protect altitude. Its also what airlines train for. Airlines and other operators train for stick shaker recoveries to minimize altitude loss. (On a low base to final turn stick shaker activation they wouldn't want to aggravate the altitude loss by pushing forward) Most airlines don't have you lose altitude in a stall situation, they want you to maintain altitude and use power and proper pitch to accelerate. See a problem with flying how you train? |
Originally Posted by DAL4EVER
(Post 561838)
Most airlines don't have you lose altitude in a stall situation, they want you to maintain altitude and use power and proper pitch to accelerate. See a problem with flying how you train?
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We are trained to react to the shaker, not the pusher...the shaker is a warning of an imminent stall, and most turbine airplanes can power out of that without losing altitude. They train on us the assumption that the most likely scenario is a shaker, and that we will not get to a real stall.
Statistically this is not an unreasonable approach...there are more shaker activations than pusher activations (I even had a shaker myself as NFP, with 30 hours in a turbojet). If you go through the shaker and get the pusher, you would then need to fall back on basic flying skills. |
Originally Posted by rickair7777
(Post 562738)
We are trained to react to the shaker, not the pusher...the shaker is a warning of an imminent stall, and most turbine airplanes can power out of that without losing altitude. They train on us the assumption that the most likely scenario is a shaker, and that we will not get to a real stall.
Statistically this is not an unreasonable approach...there are more shaker activations than pusher activations (I even had a shaker myself as NFP, with 30 hours in a turbojet). If you go through the shaker and get the pusher, you would then need to fall back on basic flying skills. |
Originally Posted by captain152
(Post 562747)
I've never heard of ANYONE getting the pusher, even in the sim.
Now you know 1. |
Originally Posted by captain152
(Post 562747)
I've never heard of ANYONE getting the pusher, even in the sim.
Or maybe the sim just sucks. :D |
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