Definition
The lowest reported intensity of structural icing, in which ice becomes perceptible on the airframe at a rate just slightly greater than it sublimates. Trace icing is not considered hazardous unless encountered for an extended period (generally over one hour), and anti-icing or de-icing equipment is not normally required.
Plain English
A very small amount of ice forming on the aircraft — just barely noticeable, and accumulating very slowly. By itself it is not dangerous, but flying in it for a long time can still become a problem.
Context Anchor
Seen in FAA icing discussions, weather briefings, and pilot reports when describing how quickly ice is forming on an aircraft.
Derivation
From the Latin tractus, meaning 'a drawing out' or 'a mark left behind.' In English, 'trace' came to mean a very small remaining amount — just enough to be detected. That same sense applies here: barely enough ice to notice.
Why Pilots Care
Tells the pilot that ice protection systems are not required and the flight can continue safely while remaining vigilant.
Grounding Statement
Picture the first thin signs of ice appearing on a surface, not a heavy buildup yet, but enough to prove the icing conditions are real.
Intuition Check
Trace does not mean “safe” or “not icing.” In this context, it means icing is present, but the amount and rate of buildup are very small.
Example Sentence 1
The pilot reported trace icing at 8,000 feet while climbing through a thin cloud layer.
Example Sentence 2
With only trace ice forming on the leading edges, the flight continued without activating the de-ice boots.