Friday, November 6, 2026 · Captain's Challenge
The Captain's Challenge.
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What combination of conditions is required for structural icing to form, and what does CARs 605.30 then require?
The answer
2Visible moisture present with the temperature at or below freezing
Explanation
Known icing conditions require two things at once: visible moisture — cloud, precipitation or visible water droplets — and a temperature at or below 0°C at which that moisture can be supercooled. TC AIM AIR 2.12.3.1: "For any ice to form the OAT must be at or below freezing with the presence of visible moisture." Cold, dry air causes no structural icing. CARs 605.30 then bars a take-off or continued flight "where icing conditions are reported to exist or are forecast to be encountered along the route of flight" unless the pilot-in-command determines the aircraft is adequately equipped for them under the airworthiness standards its type certificate was issued to.
Memory tip: Known icing = visible moisture + at or below freezing. Both, or neither.
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