Checklist: Flight Into 'Wet Snow' Can Be Deadly

It is the time of year when snowy conditions can become a factor in safety of flight.  Flight into wet snow and the associated icing conditions can lead to deadly consequences, the NTSB reminds pilots, dispatchers and operators.

Snow is typically thought to contain all-frozen water, but snowfall can contain liquid particles on the flakes or liquid particles falling among the snowflakes, commonly referred to as “wet snow”.  The liquid portions of wet snow can freeze onto surfaces that it comes into contact with, such as aircraft, and become a serious safety hazard of flight through structural, engine and windshield ice accumulation.

While “dry snow” may not pose an icing hazard, “wet snow” can. An NTSB investigation found that pilots and operators assumed flight in snow was safe as long as minimum ceiling and visibility requirements were met or that snow conditions were too dry to pose a hazard. 

Those assumptions can lead to inadequate reviews of icing forecasts or tools. “A comprehensive review of en route weather conditions, including the likelihood of wet snow and icing, can prevent accidents,” the NTSB says.

“Be aware that freezing drizzle can coexist with snow,” the FAA warns. “If you are flying into or over areas reporting snow, it is important to understand that the presence of snow does not necessarily mean that icing conditions are not present.”

What Can Pilots, Dispatchers And Operators Do?

Be aware that wet snow can freeze onto surfaces, such as the airframe, engine or the windscreen with the potential to compromise flight safety.

If faced with forecast or observed snow conditions, consider the icing threat and follow icing mitigation or avoidance procedures.

Stay updated with the latest SIGMET, AIRMET or CWA information along with pilot reports along the flight route. Ask air traffic control about pilot reports and provide reports for others in the National Airspace System of current weather conditions.

If the aircraft is equipped with leading-edge deice boots, activate them as icing is encountered unless the flight manual or pilot’s operating handbook specifically directs otherwise.

Honestly access your skill limitations. Plan ahead with cancellation or diversion alternatives.

Seek training to make sure you are proficient and understand the features and limitations of the aircraft’s equipment, especially in how to use all features of the avionics, autopilot systems and weather information resources.

Operators Should:

Include a review of the potential for icing that can accompany snow in all risk assessments for flight into snow conditions.

Make sure risk assessments include more than a review of ceiling and visibility conditions.

Check en route weather as part of the risk assessments.

Consider including information on various snow types in training programs.