Definition
Atmospheric conditions in which the rate of ice accumulation on an aircraft is so high that the airplane's deicing or anti-icing equipment cannot reduce or control the buildup, and immediate exit from the conditions is required. Severe icing is typically associated with the presence of supercooled large droplets (SLD) such as freezing rain or freezing drizzle.
Plain English
Weather where ice builds on the airplane faster than the ice protection system can remove it, so the pilot must leave the area right away.
Context Anchor
Pilots encounter this term in anti-icing and deicing system discussions, aircraft operating limitations, weather decisions, and in-flight icing procedures.
Derivation
Severe comes from a Latin word meaning serious or strict. In aviation use, severe does not simply mean uncomfortable or heavy; it points to a serious limit where the airplane’s equipment may no longer be enough.
Why Pilots Care
Severe icing can overwhelm installed equipment, leading to rapid loss of airspeed, lift, and control authority, often requiring immediate diversion or descent.
Grounding Statement
If ice keeps building even while the ice-protection equipment is being used, the airplane is in a situation that demands an exit from those conditions.
Intuition Check
Do not assume severe icing just means “a lot of ice.” In this context, it means the icing may exceed what the airplane and its equipment can safely handle.
Example Sentence 1
After noticing ice forming aft of the boots and on the windshield wipers, the pilot recognized severe icing conditions and requested an immediate altitude change.
Example Sentence 2
With anti-icing systems at maximum, the aircraft still began to lose airspeed in the severe icing conditions.