# 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.
> [!tip] The best course of action might be to turn around.
Also, be aware that getting in touch with ATC could be challenging, as they are likely busy with many planes if the weather is bad.
> [!danger] Don't hesitate to declare an emergency if the outcome of the flight is ever in doubt.
### Have an Out
Identify backup plans in your preflight planning:
1. Could you descend below freezing levels and still be above [[MEA]]?
2. Could you climb?
3. If these are cumulus-type clouds, could you stay between clouds and get out?
4. What will you do if ATC asks you to climb higher than planned?
### 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
- De-icers remove ice after formation
- Rubber boots
- Weeping wing^[Can also be considered anti-icing]
- 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)
- [[Trapped In Ice]]
#concept