Forest Service Crew Finds Out The Hard Way Abut Frozen Lake Operations

On December 2, 2010, a Super Cub with tundra tires landed on a frozen lake in Alaska and fell through the ice; everyone onboard was rescued. The Forest Service's summary notes certain things indicate that ice may not be able to support an aircraft.

U.S. Forest Serice Photo

In rivers and lakes, warm inflows from springs can create thinner areas of ice, the summary notes, and ice thickness may be thinner near shore due to warm groundwater inflow or the insulating effect of drifted snow. Ice can also be thicker near shore because of the candle-dripping effect of variable water levels.

A large, rapid drop in air temperatures causes an ice sheet to turn brittle, with the ice rendered unsafe for 24 hours. According to experienced Alaska mentor pilots, determining the thickness of ice can be very difficult. However, indicators such as “starfish”, pressure ridges, frozen bubbles, cracks, overflow, or dark spots can be used to assess the condition of the ice and indicate that it may not be strong enough to support an aircraft.

Aircraft configuration also must be considered in judging whether a frozen-lake landing is prudent. For instance, wheel skis spread weight over a larger surface area than tundra tires, reducing the pounds per square inch (psi) on a given area of ice.

Fortunately, the aircrew involved in this incident was prepared for winter operations and also possessed two satellite telephones. Just as important, the aircraft was equipped with AFF and it was being monitored by a human on the other end.

During their egress from the aircraft, one of the aircrew fell into the water and was soaked up to his chest significantly increasing his potential for hypothermia. Although this aircrew had a full complement of AMD survival gear and personal winter survival gear (heavy parkas, bibs, mittens, and hats), they were stowed in the baggage area behind the rear seat which soon became inaccessible. Shortly after arriving on shore, the aircrew started a fire, contacted their base, and awaited rescue. Because they were only 16 miles from a nearby airport, they were back home within 2 hours of the mishap. They were in luck as a massive storm was approaching the area which would have prevented their rescue for approximately two days which would have made their survival questionable.

FMI: www.doi.gov