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Icing and FIKI

Objective​

To understand the formation, dangers, and mitigation of in-flight icing and how to avoid it.

Timing​

30 minutes

Format​

Overview​

  • What is icing?
  • Hazards of icing
  • When does icing form?
  • Kinds of icing
  • Accumulation rates
  • Ground icing
  • Icing weather products
  • Icing in and around thunderstorms
  • Ice accumulation playbook
  • Flight into known icing certification (FIKI)

Elements​

What is icing?​

Aircraft icing is ice that accumulates on the structure or in the induction system and is associated with a variety of hazards.

Induction system icing (e.g. carburetor ice)​

  • Carburetor ice occurs due to the effect of fuel vaporization and the decrease in air pressure in the venturi, which causes a sharp temperature drop in the carburetor.
  • If water vapor in the air condenses when the carburetor temperature is at or below freezing, ice may form on internal surfaces of the carburetor, including the throttle valve.
  • Carburetor ice is most likely to occur when temperatures are below 70°F (°F) and the relative humidity is above 80%.
  • Due to the sudden cooling that takes place in the carburetor, icing can occur even in outside air temperatures as high as 100°F and humidity as low as 50%.
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Structural icing: Ice that forms on the airplane's exterior structure​

  • Ice tends to form on small or narrow objects
  • Types of structural icing
    • Rime ice: Rough, milkly, opaque ice
      • Forms by instantaneous or rapid freezing of super-cooled droplets as they strike the aircraft's surface
      • Formed by lower temperatures, smaller amounts of water, and smaller droplets
    • Clear ice: Slow accumulation causes smooth, clear, "glazey" ice to form
      • Formed by larger amounts of water, high aircraft speed, and large droplets
      • Water melts and "runs back" along the wing before it freezes. This can be out-of-reach of you de-icing system
      • Typically more dangerous that rime ice
    • Mixed ice: A combination of clear and rime ice

Hazards of Structural Icing​

  • Ice alters the shape of an airfoil, reducing the AOA at which the aircraft stalls
    • Note: This may have no effect in cruise but pose a significant risk during approach and landing
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  • Ice can partially block or limit control surfaces, making movement ineffective
  • Ice also increase aircraft weight
  • Roll upset can occur with self-deflection of the aileron
  • Ice-Contaminated Tailplane Stall (ICTS)
    • Since the horizontal stab is thinner than the main wing, it will accumulate ice quicker
    • A tailplane stall can occur when the tailplane exceeds its negative AoA, often after deploying flaps
    • This causes the nose to drop
    • Be on the lookout for: Sudden changes in elevator effectiveness, force, trim changes, pulsing, osilications or vibrations
    • If you suspect a tailplane stall:
      • Retract the flaps, if lowered
      • Add power and use previous airspeed/attitude combination which gave you S&L flight
  • Propeller icing
    • Ice tends to form on the spinner and inner radius of the propeller
    • This results in a loss of thrust as the propeller is less aerodynamically efficient
  • Other icing
    • Windshield icing: May severely limit forward visibility
    • Stall warning systems: May become immovable (for instance the AoA indicator on a Cirrus)
    • Antenna icing: Antennas that do not lay flush with the aircraft’s skin tend to accumulate ice rapidly
      • Radio reception may become distorted
      • Antennas can also break off with enough ice accumulation

Factors Which Affect Ice Accumulation​

  • Water content
  • Temperature
  • Droplet size
  • Aircraft design
  • Airspeed

PIREP Accumulation rates (AIM 7-1-19)​

  • Trace: Ice becomes noticeable. The rate of accumulation is slightly greater than the rate of sublimation
  • Light: Occasional requires manual activation of the deicing systems. May become hazardous after an hour in the icing conditions
  • Moderate: Requires continuous use of the deice system
  • Severe: Conditions where the deice system fails to remove ice and accumulates in places normally not prone to icing

Ground Icing: Frost​

  • Frost may form overnight when the temperature is below freezing and dew forms on the wings
  • Just like airframe ice, this can have a significant effect of the aerodynamics of the airfoil and adds weight to the airplane
  • Any accumulation of ice or frost should be removed before attempting flight
  • How to remove frost: Rag with deicing fluid, deicing fluid spray, or a light brush

Conditions Which Form Ice​

  • There is potential for icing anytime you're in visible moisture and the temperature is near or below freezing
    • Most ice forms between -20° and 0°
    • About half of reports are between -8 °C and -12 °C, and between 5,000 and 13,000 ft.
  • Cumulus clouds and thunderstorms
    • Ice can form in all levels of a cumulus cloud
    • Updrafts make SLDs and cold temperatures in the upper levels of a cumulus
  • Strataform clouds:
    • Generally trace to light
    • Often you can climb/descend out of the cloud, or descend to warmer air
  • Freezing rain: Severe ice can accumulate extremely quickly
  • Warm fronts can create the potential for freezing rain and supercooled large droplets (SLD)
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  • Freezing fog

Icing Weather Products​

  • Freezing level chart
  • AIRMETs: Moderate icing and low freezing levels
  • SIGMETs: Severe icing

Ice Accumulation Playbook​

  1. Pitot heat ON
  2. Ice protection system (TKS, boots) ON
  3. Windshielf defrost: ON
  4. Determine course out of icing conditions (climb, descend, turn)
  5. Aircraft-specific inadvertent icing encounter checklist

Removal of aircraft ice in flight​

  • Ice will sublimate after moving to clear air, but this can be very slow
  • Ice will melt if moving to warmer air

Landing with accumulated ice​

  • Be very caution of configuration changes, particularly flaps. Deploy flaps in stages
  • Perform a reduced-flap landing on a long runway, if possible
  • Carry a higher-than-normal power setting into the approach
  • Refer to the POH/AFM for approach airspeed with ice
    • Increase approach airspeed by at least 25 percent above non-icing airspeed for the applicable flap setting

Icing regulations: 91.527​

  • "No pilot may take off an airplane that has frost, ice, or snow adhering to any propeller, windshield, stabilizing or control surface; to a powerplant installation; or to an airspeed, altimeter, rate of climb, or flight attitude instrument system or wing"
  • No pilot may fly under IFR into known or forecast light or moderate icing conditions, or under IFR into known light or moderate icing conditions, unless the aircraft is FIKI-certified.

Flight into known icing certification (FIKI)​

  • "Flight into known icing": Any flight conditions where you’d expect the possibility of ice forming or adhering to the aircraft based on all available preflight information
  • FIKI is a certification process that occurs when the aircraft is developed
  • Is you aircraft FIKI certified?
    • How to tell: AFM or POH references "part 25 appendix C"
    • If your A/C has a MEL which includes icing conditions
  • Features of a FIKI airplane
    • Pitot-heat: Hotter than a no-FIKI model
    • Carburetor heat/Alternate air
    • Windshield defroster or anti-ice panel
    • Wing boots or "weeping wing"/TKS system
    • Propeller anti-ice system
    • Stall warning system heat
    • Fluid quantity gauge (weeping wing system)
    • Note some aircraft have the above features but our not FIKI-certified, like our SR22
  • Note: Even airplanes approved for flight into known icing conditions should not fly into severe icing, freezing rain or freezing drizzle.

References​