I have written that it is madness to certify light airplanes for flight in icing conditions. Some have misinterpreted that to mean that I don't think light airplanes should be equipped with ice-protection gear. Nothing could be further from the truth. I think the ice protection systems that are available today, and that are not approved for flight in icing conditions, are a great value both for the money and for the utility that they offer.
The reason that I think it is foolish to certify the systems is that certification adds to the cost and complexity without a corresponding increase in usefulness. It might also carry with it some false promise. Certification might suggest to some that the airplane is okay to fly in continuous icing conditions. No problem with flying along cracking the ice with boots or letting TKS fluid ooze out onto the surfaces. That is simply not the case.
The Cessna Caravan is fully certified for flight in icing conditions. It comes from the factory with a boot system. And, as we will see in a minute, it has a checkered history when it comes to successful flight in icing conditions. While the Caravan is not technically a light airplane it bears enough similarities in configuration and performance to be considered alongside piston singles.
First, a look at how we got to the current situation on ice protection.
Light airplanes were equipped with ice protection that wasn't approved for years. Piper Apaches, Aztecs and Twin Comanches all were offered with boot systems. A great fleet of Barons was built with unapproved boot systems as were many twin Cessnas.
The first "modern" single-engine piston airplane equipped with boots was the Cessna 210. Soon after they started putting boots on it and on the 337, Cessna decided to go for approval for flight in icing conditions. The T210 and P210 were the first single-engine piston airplanes to get that approval, in 1979. The Piper Mirage has an approved boot system as well.
As the Cessnas were approved then, they would never pass muster now. They were approved with a single power source (a quite unreliable vacuum pump) for the boots where any airplane gaining approval today will have a redundant power source, which the 210 did in later years.
Cessna did a lot of flight testing on both the unapproved and the approved systems and this yielded information that has been discussed before but is always worth a review. The value is as much for pilots who fly without ice protection as with because it outlines the performance losses with ice accumulation.
Cessna found that the often cited weight of ice isn't really a problem. According to a paper given by Cessna engineer Paul E. Leckman, the weight of an inch of ice comes to 65 pounds and the effect on performance "is negligible when compared with the aerodynamic effects of ice."
Because there was no mention of ice in Part 23, under which light airplanes are certified, the Part 25 (transport category) ice definitions were used in this study. With one inch of ice, a turbocharged 210's rate of climb dropped from over 900 feet per minute with no ice to under 100 feet per minute with FAR 25 continuous maximum icing. With deice boots and prop anti-ice (heat), the rate of climb dropped to just under 700 feet per minute in those same conditions.
From testing, Cessna came up with the following in the P210 pilot's operating handbook:
"An accumulation of ½ inch of ice on the leading edges can cause a large (up to 500 fpm) loss in rate of climb, a cruise speed reduction of up to 30 kias, as well as a significant buffet and stall speed increase (up to 15 knots). Even after cycling the deicing boots, the ice accumulation remaining on the unprotected areas of the airplane can cause large performance losses. With residual ice from the initial ½ inch accumulation, losses up to 300 fpm in climb, 15 kias in cruise, and a stall speed increase of seven knots can result. With one inch of residual accumulation, these losses can double."
All that defines ice as something to stay away from, or get out of quickly, even if you are flying an airplane with an approved ice-protection system. I would add that a lot of Cessna's information came from working with the original unapproved system but it is still valid. The system that was later approved differed only in including a boot on the vertical tail, slightly larger boots on the wing, and a different and totally unserviceable windshield heat system. I can say from experience that there is a definite performance deterioration in ice with the approved system.
Now we have evolved away from boot systems for most new light airplanes as well as from new boot installations on existing light airplanes. BFGoodrich made virtually all of the manufacturer-installed boot systems for propeller airplanes. It still vigorously supports the boot systems that are out there, and replaces systems when they wear out. The current other available and proven ice-protection system is from TKS, through Aerospace Systems and Technologies, Inc. weepingwings.com.
