Dash 8-300 prop de-icing
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Dash 8-300 prop de-icing
A silly question, but I have flown hugely and on a domestic flight this evening in poor weather Nelson-Auckland New Zealand the flight, scheduled for 60 minutes, took nearly twice as long. We climbed to 18,000 feet and then seemed to wallow for ages and then descended, at which point there was the kind of vibrations you'd worry about on a tractor: then there was a bit of prop whizzing and the pilot explained that there was nothing to worry about and that the props were being de-iced and we had descended altitude to achieve that. Two things occurred to me: doesn't a Dash 8 have electric de-icing, so why the need? And second, if the same thing happened in a really cold place like a Canadian winter, descent wouldn't help in that warming up from minus 40 to minus 30 degrees: what options would a pilot have in severe cold conditions when faced with icing?
Nelson-Auckland is scheduled at 1:25, with the upper level wind yesterday taking close to 2 hours seems about right.
The normal cruise rpm of Dash is pretty low so when ice starts to build up there can be a decent vibration, bringing the props up to max rpm is quite effective at getting the ice to shed. Yes there is electric prop de-icing but it can only do so much.
Yesterday that upper air flow was more NW so slightly warmer and at FL180 would have been nicely within the -10 to -20 C zone where ice accretion is more likely. -30 to -40 aren't such a worry for icing because there is very little moisture left at those temperature, if performance allows it can be better to climb above that -10 to -20 C zone if you start picking a fair bit of ice.
The normal cruise rpm of Dash is pretty low so when ice starts to build up there can be a decent vibration, bringing the props up to max rpm is quite effective at getting the ice to shed. Yes there is electric prop de-icing but it can only do so much.
Yesterday that upper air flow was more NW so slightly warmer and at FL180 would have been nicely within the -10 to -20 C zone where ice accretion is more likely. -30 to -40 aren't such a worry for icing because there is very little moisture left at those temperature, if performance allows it can be better to climb above that -10 to -20 C zone if you start picking a fair bit of ice.
Last edited by Massey058; 9th Jul 2018 at 01:58. Reason: grammar
I remember in the King Air, when the ice was severe enough it’d fling off the props and make a loud bang as it hit the fuselage.
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Convair 580's had a fuselage area in-line with the RH prop that had an attached shield to protect against impact damage. I assume ice as well as FOD. It can be seen in photo's if one looks carefully. Approximately 6' x 6'.
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In a Q300 if you can’t climb out of the ice with the normal 1050rpm setting used for the climb at FL180 you’ve got some decent ice accretion. Normal cruise is 900rpm, bringing the props to 1050rpm is normally enough to shed the ice and it will vibrate around a bit and shed it into the bash plates on the fuselage. If they had to go to max continuous of 1200rpm to maintain altitude or couldn’t shed the ice, the only real option is to come down to a layer where you weren’t getting the ice.
Last edited by Terrorhawk81; 15th Jul 2018 at 06:13.
