Plane crash in Montana

[Mick F]

The Pilatus PC-12 is equipped with Pneumatic De-ice Boots for both the leading edges of the wings and the vertical stabiliser. It is also equipped with Propellor De-icing and the usual probe de-icing (pitot's, static vents, temperature probes, angle of attack vanes), heated windscreen's, and finally, an inertial vane seperator (a flap which when opened, diverts heavier particle's away from the engine air intake. In this case, solid pieces of ice).

What it doesn't have (and a lot of aircraft don't), are any de-icing equipment fitted to allow de-icing of the surfaces of the wings and tailplane.

So the aircraft could have been up in very cold air for a few hours, descended into moisture, and formed what is known as 'Hoar Frost', where moisture comes into contact with a very cold surface and turns to ice instantly. If the ice has formed on the aerofoil surfaces, then the only way it can be removed is by descending into warmer air, or exposing the surface to heat (ie. the sun).

Only a small amount of ice is required on the aerofoil surfaces, for it to make a huge difference to the behaviour of the aircraft.

Mick