Why the Dangerous Ice Comes From Drops That Never Froze

Supercooled large droplet icing is the aviation hazard that starts with a cloud behaving oddly: it holds unusually large water drops that are very cold but still liquid rather than frozen. A plane flying through those drops gives them what the sky did not, and they can freeze fast onto surfaces that have no ice protection. The counterintuitive part is the sequence — the drops arrive as liquid and turn solid only on contact with the airframe, which is why NASA treats the phenomenon as its own category of icing rather than just a heavier version of the ordinary kind.