Definition
An icing condition in which the rate of ice accumulation on an aircraft is faster than the airframe's de-icing or anti-icing systems can remove or prevent it, or in which ice accumulates in locations not protected by those systems. In this condition, immediate exit from the icing environment is required because the aircraft can no longer keep itself ice-free.
Plain English
Ice is building up on the aircraft faster than the aircraft's ice protection equipment can deal with it, or it is forming in places that equipment cannot reach. The pilot must leave the icing area straight away.
Context Anchor
Seen in instrument flying and weather discussions about ice buildup on airfoils during flight.
Derivation
Severe comes from the Latin severus, meaning serious or strict. In this aviation use, it means more than simply “bad”—it means the ice buildup has become serious enough that the aircraft’s equipment cannot safely manage it.
Why Pilots Care
It can cause rapid degradation in aircraft performance and handling, requiring immediate action to avoid loss of control.
Grounding Statement
Picture ice continuing to build on the wings even after the ice-protection system is used; that is the danger in severe inflight icing.
Intuition Check
Severe does not just mean “uncomfortable” or “worse than usual” here. It means the ice is building faster than the aircraft can safely control, so remaining in it is not acceptable.
Example Sentence 1
After the PIREP reported severe inflight icing along the route, the crew requested an immediate descent to warmer air.
Example Sentence 2
The preflight briefing highlighted areas of severe inflight icing, leading to a route adjustment.