Definition
Ice formations that build forward and upward from the leading edge of an airfoil into shapes resembling horns, typically formed when supercooled water droplets strike the wing and freeze just aft of the leading edge on the upper and lower surfaces. These shapes severely disrupt airflow, causing large reductions in lift, significant increases in drag, and a sharp drop in stall angle of attack.
Plain English
Pointed, horn-shaped chunks of ice that grow out of the front edge of the wing or tail. Their shape is especially bad for flying because it spoils the smooth airflow the wing depends on.
Context Anchor
Seen in icing discussions, especially when describing how ice on a wing changes airflow and aircraft handling.
Derivation
Horn' is used here in its everyday sense of a pointed, curved projection, like an animal's horn. 'Accretion' comes from the Latin accrescere, meaning 'to grow onto.' Together the term describes ice that grows outward from the wing into horn-like shapes.
Why Pilots Care
These shapes destroy lift and increase drag far more than smooth ice, often causing stall at much lower angles of attack.
Grounding Statement
Picture ice not as a smooth coating, but as a rough ridge sticking out into the air where the wing is supposed to stay clean and smooth.
Intuition Check
“Horn” does not mean a warning horn or cockpit sound here. It means the ice has grown into a horn-like shape that sticks out into the airflow.
Example Sentence 1
After fifteen minutes in freezing drizzle, the crew noticed horn ice accretions forming on the leading edge and requested an immediate descent to warmer air.
Example Sentence 2
The airplane entered a stall earlier than expected because of horn ice accretions on both wings.