Icing and FIKI

Objective

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

Timing

30 minutes

Format

Slides

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%.
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
- 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)
- 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.