They are a dangerous mode of transportation in that the failure of the plane (or the people who are responsible for it) will cause many deaths all at once.
That isn't to say that trains and buses are great in crashes, but a flying object laden with jet fuel hitting the ground at very high speeds is going to be death sentence for nearly all on board.
Still, I feel for their families.
Statistically, air transportation is the safest mode of transportation there is.
I am a pilot. Larger commercial airliners have a system where hot bleed air is pumped into the wings via a system of pipes and coils. The Q400 uses pneumatic de-icing boots, which are not as effective as the bleed air system and only remove ice near the leading edge of the wing. In fact, if de-icing boots are cycled too soon, the ice may only be pushed outward away from the boot, rendering the boots ineffective.
The horizontal stabilizer provides a downforce, which keeps the nose of the aircraft up. Moving the elevator changes this downforce (via altering the angle of attack) and allows pitch to be controlled. If the horizontal stabilizer stalls (possibly because of icing) the aircraft will go into an uncontrollable dive, from which recovery can not be completed at the low altitude of an approach. This is called a tail stall.
Icing not only adds weight, but reduces the aerodynamic effectiveness of the airfoil. In fact, the added weight of ice is insignificant when compared to the aerodynamic havoc it causes. As power is added to compensate for the additional drag and the nose is lifted to maintain altitude, the angle of attack is increased, allowing the underside of the wings and fuselage to accumulate additional ice. In some circumstances, a light coating is all that is needed to induce control issues.
I've had some pretty nasty icing in a Beechcraft 1900D.
