The NTSB issued a Safety Alert last week highlighting the dangers of flight into snow, citing concern that some pilots don’t understand the full dangers involved in such operations.

“A recent NTSB investigation revealed that pilots and operators assumed that flight in snow was safe as long as minimum ceiling and visibility requirements were met or that snow conditions were too dry or cold to pose an icing hazard,” the Safety Board said. “Pilots also commented that snow conditions are safe to fly in as long as you can see through it; they did not consider the effects of icing.”

The NTSB added that these assumptions could serve as a disincentive for pilots to fully review icing-related forecasts or tools. “Flight in wet snow and associated icing conditions can lead to deadly consequences,” the investigatory agency further cautioned, explaining that snow is typically viewed as containing all-frozen water, but it also can have liquid particles that can freeze onto surfaces and pose safety-of-flight hazards.

An FAA Advisory Circular (AC 91-74B) states that “dry snow” is unlikely to pose an icing hazard while “wet snow” could, the NTSB acknowledged. But it said the FAA does not define either term, noting that “it is imperative that pilots and dispatchers review all potential snow forecasts for an icing threat in addition to potential instrument meteorological conditions.”