In addition to what Patrick discussed I've also read that use of the autopilot in icing situations may result in exetreme autopilot trim inputs that the pilots may not be aware of. As the icing reshapes the wing surface trim tabs are adjusted to compensate by the autopilot. A problem results when the autopilot is disconnected and the flap settings are changed producing an altered wing surface that interupts the airflow over the wing thereby inducing a stall. While the wing was able to produce lift before flap extension it was not able to produce lift after flap extension due to the ice accumulation creating an interrupted airflow over the wing.

I believe this may have been the cause of the Roselawn crash.

That's what we heard. Is that a lot of flap? I guess not. Just a preliminary setting. (?) Any amount of flaps ought to produce more lift. So? Those of you who know, please add to this discussion.

Thanks for defending the Q-400 in your essay, Patrick. I've flown aboard the aircraft several times (Horizon Air). I, too, was initially skeptical about the notion of turboprops. It took exactly one flight to put my concerns to rest.

Add in the fuel savings, and I think the Q-400 is a model for short & medium haul flights. Can't wait to see the newer, larger version to debut.

I'd like to take the opportunity and ask Patrick about the Air Florida crash in DC. From what I read, despite the instruments showing that the engine thrust was correct, the pilots felt that they didn't get enough acceleration, and they started receiving stall warning as soon as the aircraft became airborne. If I remember correctly, it was determined by the NTSB that should they applied more power immediately, the aircraft and all aboard could have been saved.

My question is: what could be the reason that they did not? My naive thinking is that if the plane does not accelerate properly on take off, the obvious thing to do is to push (or is this pull?) the levers to the metal. Could doing this cause something bad, and this was the reason why they refrained from increasing the thrust?

Flap extension does increase lift but it also increases drag so the aircraft can descend at a steeper angle and at a slower speed. The flight parameters for this to safely happen depend on a clean wing surface. Having ice on the wing creates an irregular surface that was not part of the calculations that went into determining the prescribed airspeed for a wing with an extended flap. Ice on the wing will cause the wing to stall (stop producing lift) at a higher airspeed. They were in a phase of flight where they were slowing the aircraft. Landing gear had been extended and about a minute later the initial flap setting. A moment later the aircraft became uncontrollable. At what airspeed an iced-up wing becomes uncontrollable is unknown as the amount of ice on the wing is unknowable while the aircraft is in flight.

This makes no sense to me, but that was the news headline. And that the autopilot wasn't on. I'm betting that a deadline was involved and you didn't get a chance to read about that before you sent this in. I'm looking forward to your take on the autopilot issue. I really appreciate you helping to sort out fact from fiction in airplane incidents. The media tend to sensationalize things (as you've noted).

Just a correction.

Thank you, Alchy! Interesting details. How does this jive with the Autopilot? Probably, they were just on the brink between auto and live pilot, and when they changed the flaps, the auto went nuts.

Please tell us more, those who know.

The most recent commentary from site investigator said that the plane hit the house *flat*, as in horizontal. Not at a steep angle at all. Like it just dropped out of the sky

According to an article in today's Buffalo News, two airlines have decided to stop using turboprop aircraft in the winter, including American Eagle:

http://www.buffalonews.com/home/story/579988.html

These operators obviously differ with the author as to the airworthiness of turboprops in icing conditions.

Cheers,

Flash Fludd

"Thanks to supercooled fuel in the wings, frost can form insidiously even with temps above freezing."

As a layperson in these matters (most of what I know is from being a passenger and being a reader of this column) I'd like more info on the above statement. Why is the fuel "supercooled"? Stability/volatility? Volume? Just taking guesses...

I really have no authority to answer your query (unlike many Salon members).

However, as a long-haul trucker, I know that the fuel in my tanks is significantly altered by the relative temperature. (e.g., heat causes expansion, increased vapor volume; cold contracts, thickens the fuel, minimizes vaporage). I rather imagine aviation fuel behaves similarly.

Would be interesting to learn, however, if avionics-thinkers have deduced that there's a benefit to storing avgas at low temps; indeed, if that is a practice.

Patrick, I thank you for raising the point in your article about propeller planes being no less modern or less safe than jets. "I'd like to begin by dismissing the idea, now making the rounds in some media circles, that the airplane itself, a Bombardier DHC-8-400, was somehow old-fashioned or unsafe because it happened to be powered by propellers"

It reminded me of a time I was flying with a work colleague on an ATR when he said that the airline must be running out of money to be using such old planes. Because I was aware of the fleet history of that particular airline I advised him, that at that time, the particular plane we were on was only about three years old. There is a perception that prop planes are somehow older and less reliable. Of course this is not the case. If we did not have them, smaller centres would be totally without an air service as jets are just too big to be economic on small thin routes.

The sad thing at times like this is the level of media speculation and people popping out of the woodwork to profer their opinions. The only helpful thing will be the facts and they wont be known for weeks.