Nashville CFI

Airframe Icing

Why is airframe ice bad?

Types of Ice:


Defensive Icing Strategies

The surface analysis is, by far, the best tool the winter IFR pilot has in his or her bag of icing avoidance tricks. To appreciate this fact, we must understand that all sub-freezing clouds do NOT contain icing conditions! The key to knowing where icing conditions are likely to exist can be found in the surface analysis chart.

Icing conditions are significantly more likely to be encountered along fronts. Similarly, low pressure areas, particularly along the more northerly sides of fronts are guaranteed areas of icing when air temperatures are at or below freezing.

On the other hand, finding icing in sub-freezing clouds in high pressure areas is less likely. Water droplet sizes tend to be too small and there is not enough disturbance in the atmosphere to create SLDs (super-cooled large droplets) that freeze on impact with the wings and propeller.

Please note that these are generalized observations. Icing occurs, frankly, where you find it. Understanding and using the surface analysis chart will, however, go a long way in keeping us in smooth, ice-free air.

Okay, so how do we know which sub-freezing clouds to avoid?

...We pilots should treat all sub-freezing clouds as if they contained lots of ice . . . then we should act accordingly.

Acting accordingly, of course, means having an immediate, guaranteed accessible "back door" (VFR conditions or above freezing temperatures) to bolt to should airframe icing be experienced.

Looking first at VFR conditions, here's what we're looking for:
1. Cloud bases higher than the minimum vectoring altitude
2. Cloud tops within two or three minutes climb capability.

Looking next at above freezing temperatures, here's what we're looking for:
1. Freezing level above the minimum vectoring altitude.
2. Temperature inversion with above freezing temperatures aloft.

If either of these two desired conditions do not exist, do not penetrate sub-freezing clouds.

The more stable the atmosphere, the lower the risk of icing. In stable conditions, water droplets too small to adhere to the airframe seldom grow to larger ice-creating sizes.

Fronts and low pressure areas, on the other hand, create instability in the atmosphere.

The Supercooled Large Droplet chart available here can also be a very helpful tool for pilots to avoid icing conditions.


Deice and Anti-ice Aircraft Systems

1. Airframe

Deice Boots:



2. Propeller

3. Intake

4. Fuel

5. Pitot-static