AIM ¶ 7-1-20 — Inflight Icing Definitions
AIM 7-1-20 defines inflight icing terms: rime, glaze, mixed, SLD, freezing rain, known vs forecast icing. Study guide for pilot oral exams and checkrides.
In Plain English
AIM 7-1-20 standardizes the vocabulary pilots and forecasters use to describe inflight icing. Knowing these terms helps you decode PIREPs, weather products, and your AFM's icing limitations.
Icing Types (TBL 7-1-9):
- Rime Ice — rough, milky, opaque; forms when supercooled droplets freeze rapidly on impact, trapping air. Typically conforms to the leading edge.
- Glaze (Clear) Ice — denser, harder, sometimes translucent; forms when droplets freeze slowly, often producing horn-shaped accretions on unprotected leading edges.
- Mixed Ice — combination of rime and glaze characteristics.
- Intercycle / Residual / Runback Ice — ice that accumulates between, remains after, or refreezes downstream of a deicing system cycle.
Icing Conditions (TBL 7-1-10):
- Known Icing Conditions — ice formation actually observed or detected in flight.
- Forecast Icing Conditions — conditions a weather provider expects to be conducive to icing.
- Potential Icing Conditions — manufacturer-defined temperature/visible moisture combinations in the AFM.
- Supercooled Large Drops (SLD) — drops >0.05 mm at <0°C (freezing rain/drizzle); especially hazardous because ice can form aft of protected surfaces.
The AIM notes ice type is hard to assess from the cockpit — judge by shape, not clarity or color.
AIM Source Text
FAA AIM ¶ 7-1-20See TBL 7-1-9 , Icing Types, and TBL 7-1-10 , Icing Conditions. TBL 7-1-9 Icing Types TBL 7-1-10 Icing Conditions
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Oral Exam Questions a DPE Might Ask
Q1What is the difference between rime and glaze ice?
Per AIM 7-1-20, rime ice is rough, milky, and opaque, formed by rapid freezing of supercooled droplets that trap air, and typically conforms to the airfoil. Glaze (clear) ice is denser, harder, and sometimes translucent, forms from slow freezing, and often produces horn-shaped accretions on unprotected leading edges.
Q2What are 'known icing conditions' versus 'forecast icing conditions'?
Per AIM 7-1-20, known icing conditions are atmospheric conditions in which ice formation is actually observed or detected in flight, while forecast icing conditions are conditions the National Weather Service or an FAA-approved provider expects to be conducive to inflight icing.
Q3What are Supercooled Large Drops (SLD) and why do they matter?
Per AIM 7-1-20, SLD are liquid droplets with diameters greater than 0.05 mm at temperatures below 0°C — essentially freezing rain or freezing drizzle. They remain liquid until impact and can freeze on aircraft surfaces, including areas behind protected leading edges (runback ice).
Related Paragraphs in Chapter 7
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