# Key Takeaways
- [Icing](https://www.weather.gov/source/zhu/ZHU_Training_Page/icing_stuff/icing/icing.htm) from [[weather.gov]] does an excellent job summarizing the theory
- [[Aircraft Icing]] does an excellent job summarizing the impact on aircraft
- Regardless of anti-ice or deice protection offered by the aircraft, a pilot’s first course of action should be to leave the area of visible moisture.
- This might mean descending to an altitude below the cloud bases, climbing to an altitude that is above the cloud tops, or turning to a different course.
- If this is not possible, then the pilot should move to an altitude where the temperature is above freezing.
# Details
## How Icing Affects the Airplane
> [!quote] From [[Aviation Weather Handbook]]
> Structural icing degrades an aircraft’s performance. It destroys the smooth flow of air, increasing drag while decreasing the ability of the airfoil to create lift.^[The actual weight of ice on an airplane is insignificant when compared to the airflow disruption it causes.]
Ice can form on any exposed surface, and different locations cause different issues. See [[Aircraft Icing]] for more details e.g. tail stalls.
## Types of Icing
- [[Rime Ice]]
- [[Clear Ice]]
- [[Mixed Ice]]
- [[SLD]]
- [[Frost]]
## Accumulation Rates
| Intensity | Rate | Necessary Actions |
| --------- | ------------------- | ------------------------------------- |
| Trace | less than ¼ inch/hr | Continued flight possible with limits |
| Light | ¼-1 inch/hr | Continued flight not recommended |
| Moderate | 1-3 inch/hr | Diversion necessary |
| Severe | 3+ inch/hr | Immediate diversion required |
| [[SLD]] | ++ | Immediate diversion required |
A plane that is certified for [[FIKI]] can operate in up to moderate icing (following the proper procedures for the airplane).
| Intensity | Effects^[[Icing](https://www.weather.gov/source/zhu/ZHU_Training_Page/icing_stuff/icing/icing.htm) from [[weather.gov]]] |
| --------- | ------------------------------------------------------------------------------------------------------------------------ |
| Trace | Usually not hazardous even if de-icing/anti-icing equipment is NOT used |
| Light | Occasional use of de-icing/anti-icing equipment removes/prevents accumulation |
| Moderate | Rate of accumulation is such that event short encounters become potentially hazardous and use of de-icing/anti-icing equipment or flight diversion is necessary |
| Severe | De-icing/anti-icing equipment fails to reduce or control the hazard. Immediate flight diversion is necessary| |
## Categories of Aircraft Icing
- Structural Icing: Icing on aircraft structures.
- Induction System Icing
- Air intake icing and alternative intake solutions
- [[How and Why Carburetor Ice Forms|Carburetor Icing]]
- Instrument Icing
- Icing on pitot tube, static port, antennas, etc.
## Icing Avoidance
### Icing Conditions
In general, any time^[This is really common advice, but Jack could not find a specific source for it. Please let me know if you have one.]
1. outside air temperatures of +10°C or less, and
2. visible moisture is present
Certain fronts and atmospheric structures are more likely to cause icing conditions.
Typically, ice only forms within a 2000'-3000' layer,^[From [Aircraft Icing: Everything You Ever Wanted to Know](https://www.youtube.com/watch?v=BNUekm12_xM)] so descending may help. (Climbing may also help, but also increases the risk of [[SLD]].) A key initial goal is to stop the accumulation.
### Flight Into Known Icing Conditions
Aircraft certified for [[FIKI]] need to have specific tests completed. All equipment must be functional to fly into known icing conditions.
> [!question]- There is a PIREP for light icing along your intended route. Can you fly a C172 there?
> No, under no circumstances, since it is not certified for [[FIKI]].
>
> For more on known ice vs known icing conditions, see [[Bell 2009]].
## Equipment
- Anti-icers prevent ice from forming
- Pitot heat
- Carburetor heat
- Windshield defroster
- Fluids released from leading edge of propeller or wing
- De-icers remove ice after formation
- Rubber boots
- Weeping Wing
- You may be able to knock some ice from a constant-speed propeller by varying the pitch
> [!youtube] Published by [[Air Safety Institute]]
> 
> [!info] For more information on icing equipment, see [Deicing and Anti-Icing Equipment](https://www.aopa.org/training-and-safety/online-learning/safety-spotlights/weather-wise-precipitation-and-icing/deicing-and-anti-icing-equipment) from [[AOPA]]
# Additional Resources
- [[AIM 7]]-1
- Advisory Circular
- [[AC 91-74]]
- [[Aircraft Icing]]
- [[How to Properly Use an Icing Forecast]]
- [[How and Why Carburetor Ice Forms]]
- [Aircraft Icing: Everything You Ever Wanted to Know](https://www.youtube.com/watch?v=BNUekm12_xM)
- From [[Air Safety Institute]]
- [Beyond Proficient | IFR Series: Avoiding Icing](https://www.youtube.com/watch?v=gOUkAq8oWy0)
- [Accident Case Study: Trapped in Ice](https://www.youtube.com/watch?v=7rryvSQhK7k)
#concept