Calgary's Kenn Borek Air heads out on medical rescue mission at Antarctic station

Two Twin Otter planes from Calgary-based Kenn Borek Air are on their way to the South Pole to carry out a medical evacuation.

One will stay at the British station Rothera for search and rescue purposes, while the other will travel on to the Amundsen-Scott Research station at the South Pole.

The planes left Calgary on Tuesday morning and aren't expected to arrive at their destination until Sunday.

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The National Science Foundation says a seasonal employee with Lockheed Martin at the Amundsen-Scott station requires hospitalisation and must be flown out. No further personal or medical information is being released in order to preserve the patient's privacy.

Foundation spokesman Peter West says they don't normally schedule flights for this time of year because of darkness and the extreme cold, which hovers at around -60 C during the winter months. He says they're monitoring the situation closely to see when the weather will co-operate.

"We're keeping a careful eye on the weather, I don't know what the window is that far out."

The Canadian-builtTwin Otter is designed to operate in extreme weather conditions.

Willard Hagenwas a bush pilot and owned Aklak Air in Inuvik, NW.T.He knows the aircraft well.

"The engine's performance really doesn't change on a turbine whether it's minus 60 or 40 below or plus 40 C. So they're the ideal airplane for any remote location that they're flying into," he told CBC Radiohost Donna McElligott.

Thisis the third time in 15 years thatKennBorekAir has carried out similar flights, with the other evacuations occurring in 2001 and 2003.

The company made improvements to its navigation charts for the Antarctic after three Canadians were killed when a Kenn Borek plane crashed into an Antarctic mountainside in January 2013.

The bodies of Bob Heath, 55, of Inuvik, N.W.T., Perry Andersen, 36, of Collingwood, Ont., and Mike Denton, 25, of Calgary remain on Mount Elizabeth, entombed in the wreckage of the plane in which they died.

Transportation Safety Board investigators were unable to pinpoint the cause of the crash.