Hopefully you know this: When one is talking about aircraft, a "stall" has nothing to do with the engines. A stall is when airflow over the wings is disrupted so that lift is lost. Almost all heavier-than-air aircraft can stall if the conditions are right, though some airplanes don't so much as stall as mush in a downward direction.
Icing does a few bad things to airplanes. The weight of the ice adds to the weight of the airplane, which increases the amount of lift needed to keep it flying. All other things being equal, a lightly-loaded airplane stalls at a slower speed than a heavily-loaded airplane. By increasing the aerodynamic drag on the airplane, ice accumulation adds to the amount of thrust needed to keep the airplane moving at a given speed. If not enough power is added to compensate for the additional drag, the airplane will stall. Ice accumulation also alters the airflow over the lifting surfaces, making them less efficient, which also raises the stall speed. When an airplane is approaching an airport in icing conditions, the airplane has landing gear hanging out and flaps (and maybe slats) that are not protected by anti-icing equipment, which gives ice even more places to adhere to the airplane.
It is not just the wing that can stall. The horizontal surfaces on the tail (tailplane) can also stall. On many airplanes, the center of lift is behind the center of gravity, so the tailplane exerts force in the downward direction in order to stabilize the airplane in flight.
If the tailplane stalls, the lever arm between the center of lift (pressure) and the center of gravity will work to pull the nose down and pull it down hard. 
(Elevators control pitch, ailerons control roll and the rudder controls yaw.)If the wing itself stalls, the nose also drops. The difference is that in normal conditions, the wing stalls before the tail, so the pitch angle can be controlled somewhat. In a tailplane stall, pitch control is effectively lost. The pilot needs to gain airspeed, which means the pilot will push the throttles in, as that is the only tool left.
(All this ruminating is speculative, of course. I probably have no business offering any conjecture on this, but what the hell, this is my blog. And like any good blogger, my job is to shoot my mouth off about things of which I have limited knowledge.)
Without knowing a damned thing more than what has been in the news, and having never gotten close to a DeHavilland Dash-8, please take this all with a grain of salt, but I would be rather surprised to learn that Colgan Flight 3407 went down for any cause other than icing and, quite possibly, ice that caused a tailplane stall.
4 comments:
Based on my limited knowledge of aircraft aerodynamics, your explanation sounds pretty reasonable to me, and certainly better than anything that's likely to come out of the MSM.
Yes and you are more than likely to be right.
Dash 8's are flown here but land 20 miles to the west in Hayden where there have been two small plane crashes recently.
Rocky Mountain Airways flew 7's into this airport at one time. Those and the 8's are some of the best mountain planes at least that's what I'm told.
Have flown in 8's several times and liked them. The approach into this one is difficult and there is a hump in the runway such that you can't see the other end. There are no instrument landings at either airport.
Most who read your post will come away with something they will remember. Nice job Misfit!
having ridden 8s and 7s many times they are great birds with excellent short field (7 was STOL) and good passenger comfort. However like most T-tails the tail interaction with propwash isnt' there (less down force) and you explanation is most likely valid.
Still a good bird but smaller commuters and ice have proven to be a a good reason for the crew to pay attention and get on the ground.
Eck!
My guess is icing as well. They were probably at normal approach speed and when the flaps were selected down and were in transit, the change in aircraft attitude stalled the tail plane.
I used to work for Rocky Mountain Airways and and have a long history with the Dash 7 (Was there when the first one was delivered, SN 4). That aircraft's attitude changed dramatiaclly (nose down) when flaps were deployed. the Dash 7 was designed as a STOL aircraft while the Dash 8 was not although quite a few of the features from the "7" were used on the "8" (spoilers, full span flaps, high wing, T Tail etc).
Awful tradgedy.
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