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of inflight ice, a pilot report is mandatory and should include the type of ice and level of intensity: trace, light, moderate or severe. ATC will also want to know the OAT at the time of the encounter. The gamut of systems to combat these types of icing runs from liquid, to pneumatic boots, to electrically heated components, to bleed air systems. Each system presents varying degrees of weight, cost, effectiveness and reliability.Thermal SystemsA thermal system (bleed-air or electric) may operate one of two ways: fully evaporative or wet. In the evaporative case, sufficient heat is provided to cause supercooled water to completely evaporate. This has the advantage of protecting the aft, unheated portion of the airfoil. A wet thermal system can only prevent water from freezing. It requires less energy but it can fail to prevent runback ice, which forms when the running water passes aft of the protected surface and freezes. Even a fully evaporative system may transition through a wet phase as it heats and cools. The ideal method for operating a fully evaporative system is to activate it prior to entering potential icing conditions, thus allowing the surface to stabilize at the required temperature.Electro-thermalElectro-thermal systems use resistive circuits buried in the airframe, windshield or propellers to generate heat. The system only needs to melt the contact layer of ice for wind-shear to then shed the remainder.TKS (Tecalemit – Kilfrost – Sheepbrige – Stokes)The TKS system uses a glycol- based fluid which exudes through 0.0025-inch-diameter holes in panels on the leading edges of the wings and horizontal stabilizers. The fluid lowers the freezing point of water preventing it from freezing and adhering. The systemcan be installed as a known-ice or non-hazard system depending on redundancy, additional components and type of aircraft.Pneumatic BootsThe most common deicing system for GA aircraft, including some jets, uses pneumatically inflated rubber boots on the leading edges of airfoil surfaces. This normally includes the wings and empennage, but may also include struts and cargo pods. The system uses relatively low pressure air to rapidly inflate and deflate the boot. The principal drawback to boots is the aircraft will operate with ice accretions for the majority of the time in icing conditions and it provides no protection from runback ice. Also, the only time it will be free of ice will be immediately after cycling the system.Ancestor Worship: Ice BridgingEarly pneumatic boot designs had relatively low volume air supplies to draw from, and were slower to inflate and deflate. A phenomenon which was thought to be occasionally observed with these systems was known as “ice bridging,” in which the boot expanded under the ice and stretched it without breaking its structure. This led to a space beneath the ice shape which allowed the boot to subsequently inflate and deflate with no effect. The problem was addressed by allowing a particular thickness of ice to develop before inflating the boot. Once the requisite thickness was attained, the boot inflation would shatter the ice and clear it off the surface. With the current, rapidly inflating systems, there is almost no evidence which supports the existence of this phenomenon.From the NTSB in 2008: “For 60 years, pilots have been taught to wait for a prescribed accumulation of leading-edge ice before activating the deice boots because of the believed threat of ice bridging. In theory, ice bridging could occur if the expanding boot pushes theice into a frozen shape around the expanded boot, thus rendering the boot ineffective at removing ice. The Safety Board has no known cases where ice bridging has caused an incident or accident......” Leading-edge deice boots should be activated as soon as icing is encountered, unless the aircraft flight manual or the pilot’s operating handbook specifically directs not to activate them.Exit StrategyIcing accidents result from a combination of increased weight, increased drag, loss of lift, and a decrease or loss of thrust caused by induction air blockage and propeller or compressor blade contamination. Whether thermal, “weeping wing” (a.k.a. TKS) or pneumatic, deice systems give your aircraft more utility and safety but are designed to get you out of a bad condition. Avoid ice as much as possible (standard temperature lapse rate is 2.0°C / 3.5°F per 1,000 ft.) and exit it promptly when encountered. Because of accumulation on unprotected areas, consider adding a few knots to your configuration and approach speeds. Know your system, test your system and don’t hesitate to use it early. If you demand one iota more than it can give, you may find yourself wishing you were onthe ground. T&T •Kevin Dingman has been flying for over 40 years. He’s an ATP typed in the B737 and DC9 with 21,000 hours. A retired Air Force Major, he flew the F-16 then performed as a USAF Civil Air Patrol Liaison Offi- cer. He flies volunteer missions for the Christian organization Wings of Mercy, is employed by a major airline, and owns and operates a Beechcraft Duke. Contact Kevin at Dinger10d@gmail.comNOVEMBER 2016 TWIN & TURBINE • 21