FIRST, let me stress I am NOT assuming the cause of this particular accident.
With the news media currently focusing on aircraft icing I am wondering:
What is the DEAL with ice and turboprops????
Obviously turboprops are down in the weather for a greater proportion of flight time than jets. But most accidents I remember hearing about have happened in the approach phase.
Just a very vague and quite possibly incorrect observation, but it appears the majority of icing accidents in jets occur in the takeoff phase, and the majority of those in turboprops occur in the approach phase. It also would appear that a greater proportion of icing accidents occur in turboprops than jets.
Anyone able to shed some light??
Well, as I'm sure you know, most jets have a much more effective ice protection system than the inflatable boots found on recips and turboprops. Most jet designs have enough excess thrust to allow very hot bleed air from the "high pressure compressor" stages of the engines to be tapped and piped directly to the wings and/or stabilizers, all simultaneously (as long as all engines are operating anyway). Those polished metal surfaces you see on the leading edge of jet wings and stabilizers contain tubes through which this hot air flows and disperses througout the forward sectoin of the airfoils. This hot surface heats the air as it flows over the airfoils, melting accreted ice and preventing additional ice from forming.
Conversely, most turboprops rely on pneumatic boots that inflate to "break the ice". In the case of the Dash 8 I've heard it happens one at a time.....for instance left wing boot activates, then right wing, then stabilizer, etc. I can only assume this is because most turboprop designs aren't capable of producing enough hot bleed air to use the typical jet ice protection designs.
Why would jets encounter problems on takeoff? The fan air intake on a turbofan produces a large pressure drop due to rapid acceleration of the air as it is sucked in. This produces a carbeurator-like temperature reduction which can be catastrophic if Engine Anti-Ice is not selected on when visible moisture is present, even at tempratures well above freezing. Also, I can't speak for other operators, but we typically take off with the APU as the bleed source in our jet and it is not capable of providing enough hot air to opeate the ice protection sytem. This is done to avoid pressurization fluctuations due to variation engine thrust during takeoff and initial climb. If care is not taken to recognize icing conditions and select the engine bleeds open for takeoff, problems could occur. Once you're in the air however, the hot-wing system on most jets is quite effective.....I don't think I've ever seen ice on the leading edges after landing and I've flown in a fair bit of winter weather.
Although the turboprops' boots are enough in most situations, I can only speculate that those systems just aren't as effective as piping hot air directly to the surfaces. Perhaps this is why the jets coming into BUF that night did not experience catastrophic problems while this aircraft did. Don't get me wrong, even in a jet with a great ice protection system, you still avoid ice and get out of it ASAP when you encounter it.