Snow and ice buildup on aircraft (especially the wings) is a well-known and feared hazard of cold-weather operations; it roughens the surface of the wings and changes their profile, which combine to enhance the tendency of the airflow over the wings to separate from the surfaces of same, and thereby decrease (often by a large amount) the amount of lift generated, change (sometimes markedly) the distribution of the remaining lift, decrease (frequently by several degrees) the attack angle at which the aircraft stalls, and alter (sometimes greatly) the aerodynamic forces acting on the aircraft’s flight control surfaces. Snow and ice can also block (partially or completely) aircraft sensors, including those for such critical parameters as airspeed or engine thrust.
While icing is dangerous whenever it occurs, most icing-related accidents seem to fall into two categories:
Aircraft crashing on takeoff due to snow, ice, frost, etc., accumulating on the wings prior to takeoff as a result of no/inadequate/inadequately-recent anti-icing; in these accidents, the main factors are the loss of lift (causing the aircraft to take much longer and require much higher speeds to take off successfully, or even to be completely unable to lift off, period, or to climb out of ground effect after lifting off), the altered lift distribution (which, in most airliners, generally takes the form of a forward shift in the center of lift – as most transport aircraft other than the very smallest and slowest have rearward-swept wings, and the wingtips tent to freeze before the wing roots – resulting in a strong pitch-up tendency during rotation, or even in the aircraft spontaneously rotating early all on its own, and making it very easy to rotate the aircraft too far, all of which increase both drag and the risk of accidentally stalling the aircraft), and the decreased stall angle (which greatly increases the risk of a stall, especially when combined with the aforementioned pitch-up tendency, and especially especially because most stall warning systems sense only the aircraft’s attack angle, rather than directly detecting the airflow separation associated with an impending or actual stall, and are calibrated for ice-free conditions, meaning that, in icing conditions, the aircraft can stall at an attack angle well below that at which the stickshaker activates and the man in the box yells “STALL” at you). Examples include Ozark 982, Continental 1713, Air Ontario 1363, USAir 405, and Air Florida 90 (the last of these was additionally affected by blocked engine sensors, which tricked the crew into choosing a power setting that would have been dangerously low even without airframe icing).
Aircraft falling out of the sky due to ice accumulating on their wings during flight as a result of encountering freezing rain or drizzle combined with non-use/inadequate use/inadequacy of the aircraft’s onboard deicing systems; in these accidents, the main factors are the changes in the aerodynamic forces imposed on the aircraft’s control surfaces (causing – as ice accumulation is frequently asymmetrical, and, even if, by some miracle, the aircraft does accumulate ice symmetrically, this symmetry is soon lost when ice starts to shed from the wings, as this process is random and essentially never symmetrical – a steadily-increasing force asymmetry on the aircraft’s ailerons; if the crew are flying the aircraft manually, they need to apply more and more force to their yokes just to keep the aircraft level, while, if the autopilot is flying the plane, the forces imposed on the aircraft will eventually exceed its control authority, causing its disengagement and an immediate violent roll, likely resulting in at least a temporary loss of control), the altered lift distribution, and the decreased total lift and stall angle (all of which make it more difficult to recover from the steep dives that generally follow a loss of control, and increase the likelihood that something will have some limit or another exceeded in the process). Examples include American Eagle 4184 and Comair 3272.
Given the dangers posed by icing, are there any aircraft designs that are relatively unaffected by snow/ice/frost/miscellaneous solid water accumulation?
I can think of a few possibilities:
Aircraft with very low wing loadings (i.e., very large wings for an aircraft of their weight) could be more likely to have sufficient excess lift to overcome the decrease in lift resulting from ice accumulation.
Delta-winged aircraft in subsonic flight do not rely on attached airflow to generate lift, but, rather, exploit flow separation and the resulting vorticies to generate a low-pressure area above the wing and produce lift; thus, they could reasonably be expected to be resistant or immune to the decrease in lift, altered lift distribution, altered flight-control forces, and increased stallability caused by flow separation consequent to icing, or even possibly see an increase in lift thanks to icing-enhanced flow separation.