Deicing and Anti-Icing Equipment

Safety SPOTLIGHT: Precipitation and Icing

Most light aircraft are poorly equipped to deal with icing conditions. Some may have partial equipment intended only for escaping unexpected icing conditions. Unless your aircraft is FAA certified for flight into icing conditions, you must avoid entering areas of known icing.

Even airplanes approved for flight into known icing conditions should not fly into severe icing.

Known Icing

How do you know if “known icing” conditions exist? Known, observed, or detected ice accretion is actual ice that is observed visually on the aircraft by the flight crew or identified by on board sensors. During preflight and inflight stay alert to and be aware of icing potential:

Check for PIREPs of icing near your route of flight
Keep situational awareness with onboard satellite/datalink equipment
Review G-AIRMETs, which graphically depict icing and freezing levels
Review forecast for icing potential along your route

Basic Anti-Icing Equipment

On most light GA aircraft basic anti-ice equipment to prevent ice from forming includes pitot heat, carburetor heat (if the engine is carbureted), and a windshield defroster.

Pitot Heat—It’s a good habit to always turn the pitot heat on before flying through visible moisture. If ice blocks the pitot tube the airspeed indicator will stop working properly. If the pitot tube drain hole also gets blocked, the airspeed indicator will act like an altimeter and erroneously show increased airspeed when the aircraft climbs.

Carburetor Heat/Alternate Air—Apply carburetor heat, which uses heat from the engine, to prevent or remove carburetor icing. For fuel-injected engines use the alternate air door if the primary air intake ices.

Windshield Defroster—Use the defroster to help prevent ice from forming on the windshield. Be aware that in moderate or greater icing conditions the defroster may not keep up with accumulation.

Advanced Anti-Icing Equipment

Windshield Anti-Ice—There are two systems used in light aircraft. An electrically heated windshield (or plate) or a fluid spray bar located just ahead of the pilot’s windshield.

Propeller Anti-Ice—Ice often forms on the propeller before it is visible on the wing. Props are treated with deicing fluid applied by slinger rings on the prop hub or with electrically heated elements on the leading edges.

Deicing Equipment

Deicing equipment removes structural ice after it forms. The two most common GA systems are inflatable boots and weeping wings. Weeping wings also can be considered anti-icing equipment if the fluid dispensing system is activated before ice accumulates.

Inflatable Boots—When activated, the inflatable rubber strips—attached to and conforming to the leading edge of the wing and tail surfaces—are pressurized with air and expand, breaking ice off the boot surfaces. Suction deflates the boots and they return to their original shape.

Weeping Wing—When activated, the deicing system pumps fluid from a reservoir through a mesh screen embedded in the leading edges of the wings and tail. The liquid flows all over the wing and tail surfaces, deicing as it flows. It can also be applied to the propeller and windshield.

FAA Certificated vs. Non-Hazard Systems

What’s the difference between systems that are FAA approved for flight in icing conditions, which allow a pilot to legally challenge routine icing conditions, and “non-hazard” systems that do not? Basically: certification standards and testing. Approved systems have demonstrated that they can protect your airplane during icing conditions specified in the airworthiness regulations, while non-hazard systems do not have that burden of proof. In the case of non-hazard systems installed on airplanes certificated before 1977, non-hazard systems weren’t even required to prove that they could shed ice!

Deicing equipment removes structural ice after it forms.

Approved Systems Certification

Among many other tests, the manufacturer of icing equipment approved-for-icing-condition flight must determine an airplane's tolerance to ice accumulation on unprotected surfaces during a simulated 45-minute hold in continuous maximum icing conditions, which indicates icing conditions found in stratus clouds. Unprotected surfaces include such items as antennas, landing gear, fuselage nose cones or radomes, fuel tank vents, fuel tip tanks, and the leading edges of control surfaces. In addition, ice on protected surfaces—such as deicing boot residual ice or runback ice from a thermal ice protection system—must be accounted for.

Comparison of Non-Hazard vs. Approved Systems:

Requirements	Non-hazard System	Approved for Flight in Icing Conditions System
Stall warning heat	Not Required	Required
Reliability standards (redundant power sources)	Not Required	Required
Critical area protection	Not Required	Required
Shown to perform intended function	Required	Required
System safety analysis Evaluate loss of ice protection system Determine if system failures create a hazard	Not Required Required	Required Required
Electromagnetic interference testing	Required	Required
Fluid reservoir capacity requirements (e.g.,150 min. @ normal flow rate) Fluid quantity gauge	Not Required Not Required	Required Required
Propeller thrust not affected by icing	Not Required	Required
Air data (pitot, static, angle of attack, stall warning) and other systems function normally in icing	Not Required	Required
Icing system function annunciation	Not Required	Required
Testing to show that the airplane has adequate performance, stability, controllability, stall warning, and stall characteristics for expected ice accretions	Not Required	Required
Susceptibility to ice shedding damage	Not Required	Required
Certified for flight in freezing drizzle or freezing rain	NO freezing drizzle or freezing rain	NO freezing drizzle or freezing rain

FIKI

Even airplanes approved for flight into known icing conditions (FIKI) should not fly into severe icing. Many Approved Flight Manual or Pilot Operating Handbook Limitations Sections require an immediate exit when these types of conditions are encountered.

Note: Airplane certification for flight into known icing conditions does not include freezing drizzle and freezing rain. In fact, some airplanes are prohibited from flying into freezing drizzle or freezing rain, regardless of its intensity. These conditions are very dangerous and can cause ice to form behind the protected areas.

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