Of all the FAA’s aircraft certification standards the one for flight into icing conditions is the most ridiculous. We pilots usually call the approval flight into known icing conditions, or FIKI, but the FAA regs don’t actually use the word “known.” As far as the rules go, icing is icing whether you knew it was there or not.
The technology to remove ice from airplanes dates back at least to the 1930s when Goodrich pioneered development of the pneumatic deice boot. Some airline airplanes in the piston era had heating systems to melt ice. Even the anti-ice fluid TKS system technology traces its roots to England in World War II. The battle against airframe ice is as old as flying in cold clouds.
But the idea of granting approval to fly into icing conditions, and to certify that the airplane’s systems can handle the ice, is relatively recent. The rules for flight into icing certification were developed for transport airplanes, those that weigh more than 12,500 pounds for takeoff, and those same rules intended for large, powerful airplanes, have been adapted, sort of, to fit piston singles and twins.
Piston airplane makers have offered ice protection systems for many decades, particularly on twins. Deice boots were glued to the leading edges, the props were protected either by a spray of alcohol or by electric heaters on the blade roots, and that was it. As the pilot of one of these airplanes you knew that the ice protection system would give you extra time to escape icing if you flew into it, but the idea that the airplane was now capable of intentionally flying into ice, and continuing in icing conditions, was absurd.
An airplane with boots was no more “approved” for flight in icing than one with weather radar was approved for flight into a thunderstorm. The radar gave the pilot a tool to avoid thunderstorms, and the boots gave the pilot a way to escape icing.
The turbine engine was probably most responsible for development of ice protection certification standards because a turbine engine just won’t continue to operate if much ice forms on its air inlet. The ice will either choke off the essential air supply or break off and damage the compressor blades of the engine, or both.
The turbine engine with its supply of very hot air that could be siphoned off from the compressor also makes it possible to provide true ice protection that other systems simply cannot. The hot air can heat the leading edges to hundreds of degrees, so hot that water is vaporized on contact so that ice can’t form, nor can the water run back and refreeze on the wing. Because it was possible to truly protect a jet from ice, the FAA wrote rules that were intended to make sure those airplanes were protected.
But it took time for the rules to catch up with the jets. The Saberliner, for example, had no ice protection for its wing leading edges. The first Learjet, the Model 23, had heated wing leading edges, but was not approved for flight in icing. And that was true of some other airplanes early in the jet age.
Because icing – like turbulence, rain, hail, or snow – is a weather phenomenon that can range from light to extreme, how do you define what icing is in order to certify an airplane to fly in it? The FAA’s own definition of severe icing for pilot reports says that severe icing is building so rapidly that normally functioning – and certified – ice protection systems can’t keep up. So in one place, the AIM, the FAA says icing that can overwhelm an airplane certified for flight into icing can exist, but then certifies the airplane for flight into icing anyway. Does that make sense?
The really difficult and expensive part of icing certification is not to demonstrate that a system prevents or removes ice, but to find icing that meets the certification standard. The rules require specific amounts of total moisture, a specific size of droplet, and – of course – specific air temperatures. All of these conditions do exist in nature, but to find all of them at once in the same parcel of air is difficult. Manufacturers spend untold hours flying to where icing is forecast and then use laser-based instruments to measure the conditions to make sure they match the FAA standards. It takes more luck than skill to find and fly into the “natural” ice the rules require, and a certification program can be held up for weeks or months looking for those conditions.
The useful ice testing is done using “ice shapes.” Sections of a wing or tail are put into an icing tunnel that can duplicate the certification standards for all conditions. The tunnel “grows” ice on the leading edge and that shape is then duplicated in some lightweight material which is then glued to the airplane wings and tail. Computer software can also predict the shape ice accretion will form and that may be acceptable. In any case, test pilots have to take off with these horrendous rough, horn-shaped globs on the leading edge and go out and see how the airplane performs, particularly near stalling speed. If the airplane handles okay with the shapes on a pilot can have confidence he can get the iced up airplane down to a runway.
But I worry that these tests that are really designed around the huge reserve of power in a jet don’t really apply to piston airplanes. I fear a FIKI approval sends the wrong message. Don’t get me wrong, I want to see ice protection on any airplane that flies IFR because at some altitude any time of the year there are clouds that can contain icing conditions. But I don’t believe that a piston airplane with icing certification is necessarily more capable than one that has ice protection that has not been certified. Maybe the FIKI airplane can handle more ice, but I do know there are conditions that it can’t handle.
Icing certification adds big bucks to the cost of an ice protection system on a GA airplane and buys the pilot little or nothing, and may even mislead him into a situation he would have avoided without the approval. I like the old system better. The ice protection is there, and it works and will handle some ice; use it to get out of icing immediately. Leave the “known” out. If you know ice is there, don’t fly into it in a piston airplane.