the peak of the Antarctic summer, the ice runways aren't able to support the weight of wheeled aircraft and only planes that can take off and land on skis can operate. For transportation across vast distances around the continent, the Program uses a combination of ski-equipped LC-130s and ski-equipped Basler BT-3 and Twin Otter planes through a contract with through Kenn Borek Air, Ltd.. Ski-equipped planes can land on groomed and maintained ski runways like those at Amundsen-Scott South Pole Station and other field camps, or in relatively smooth ungroomed snow. Helicopters The program maintains a small fleet of helicopters, under contract, at McMurdo Station to transport people and cargo around the immediate area of the station. Helicopters also carry scientific survey equipment and reconnoiter landing and scientific sites. Occasionally some of the helicopters will be temporarily set up at larger field camps to enable transport around an otherwise inaccessible region. The current helicopter support contract is held by Air Center Helicopters. Traverses Tractor-pulled convoys or “traverses” are used to transport large quantities of fuel and cargo across large distances. Every year three traverses carrying more than 100,000 gallons of fuel drive the from McMurdo Station to Amundsen-Scott South Pole Station to deliver fuel for the next year. Other "science traverses" transport heavy science equipment to field sites hundreds of miles from the station. Vessels/boats The program maintains two research vessels, RVIB Nathaniel B. Palmer and ASRV Laurence M. Gould. The ships are used to both transport people and supplies between Palmer Station on the Antarctic Peninsula, and the port at Punta Arenas, Chile, and to embark on longer science-focused voyages to understand the Southern Ocean or visit other remote areas of the continent. Smaller boats at Palmer Station, including inflatable rafts and larger rigid-hulled inflatable boats, are used to transport scientists around the islands near the station. McMurdo Station is resupplied by ship at the end of every summer season. The U.S. Coast Guard heavy icebreaker Polar Star cuts a channel for a cargo ship to pass through and reach the ice pier at the station. A fuel tanker usually follows the cargo vessel to deliver fuel. Vehicles and transport The Program has a fleet of vehicles to meet a range of needs at each station. A variety of large and small loaders are used to move cargo and other heavy equipment around. Tracked vehicles, including PistenBullys and Hagglunds