Certifying airplanes for flight in icing conditions is a fairly new regulatory concept, particularly for non-transport category airplanes. I know, everybody calls it FIKI for flight in known ice certification, but the rules, such as they are, call it icing, not known icing.
For decades airplane manufacturers installed ice protection equipment on a variety of airplanes with no certification implication at all. Deice boots were common in the 1930s on multi engine airplanes. Propellers were protected by slinging alcohol on the blade roots, and the same stuff was used to prevent ice formation on windshields.
Electrically heated propellers and windshield hot plates became common many decades ago. And the weeping fluid TKS anti-ice system dates back to WW II when it was used on British bombers. All of the Hawker 125 series jets use TKS starting in the early 1960s. TKS seems new to piston owners, but is nearly as old as boots in the ice wars.
Many thousands of GA twins from Beech, Cessna, Piper and others were equipped with boots and prop ice protection but nobody thought about certifying the airplane to fly in ice. The boots were tested at least some, they worked in terms of inflating on command, and usually broke the ice off.
Think of all of the Beech 18s and Cessna 400 series twins that slogged through all kinds of weather, including icing, working for a living. And they were not certified for icing. Neither was Piper’s Aztec or the initial run of Navajos. Or the Aero Commanders, or even the Learjet 23 or Saberliner.
The idea of certifying an airplane with ice protection for flying in icing made as much sense as certifying a weather radar equipped airplane to fly in thunderstorms. Radar helped you avoid the worst and the boots kept you flying while you escaped the ice. Everybody knew there were thunderstorms that could break the wings off, and that there is icing that can overwhelm any ice protection system.
Certifying for flight in icing really took hold as turbine engines came along. It quickly became obvious that ice building on the inlet to a turbine engine could choke airflow and kill the engine. Equally threatening was ice that built up on the engine inlet and then broke off and was swallowed in chunks that could destroy compressor and turbine blades. Something had to be done.
So standards of liquid water content and droplet size were devised to test engine inlet ice protection. Then the concept of testing and approving ice protection spread to the rest of the airplane. But the “rules” were contained in FAA advisory circulars, not actual certification rules, and the ACs applied only to transport category airplanes which weigh more than 12,500 for takeoff.
I’m not sure why, but in the 1970s Cessna decided to certify some of its piston airplanes for icing. The 337 Skymaster and 210 singles were first up. The only procedures that existed applied only to transport airplanes, not GA piston airplanes, but the FAA somehow adapted those standards to the 337 and 210 and they were certified for icing.
You don’t need much experience in weather flying to know that an ice certified 210 is not going to survive as much ice as a non-certified King Air, or Beech 18, or even Cessna 310. If nothing else the 210 engine would cook because ice buildup on the cowling restricted cooling air flow just at the time you needed every single horsepower to lug the ice the system couldn’t remove.
So now pilots were told it was OK to fly a “certified” piston single into icing. Before that pilots were told to stay out of icing, and if you find it activate the boots and change altitude, or course or do something to escape. Was icing approval a safety advance? I don’t think so.
There are thousands of airplanes—nearly all piston twins—that are equipped with ice protection but are not approved for flight in icing. Nor are they specifically prohibited from flying in icing. A perfect status, I say. If you know ice is there nobody flies into it. If you find icing, you do your best to exit. Who needs to certify that?
But it’s too late. The FIKI horse is out of the barn. Airplanes are being certified to fly in laboratory icing and pilots are given a level of comfort that may not be warranted. And now an AD is being issued to prohibit flight in icing for thousands of Cessna twins that were built and equipped under the old concept of not approved, but not prohibited. Icing should get every pilot’s attention no matter what the certification limitations of the airplane may be and new limitations shouldn’t change that.
I applaud icing tests and the improvements they can lead to. And I’m happy to see effective ice protection on a growing variety of airplanes. But I much prefer the old attitude that ice protection helps you escape, but there are icing conditions out there that can bring down any airplane, particularly any piston powered airplane no matter the certification status.