Two Calgary bush planes are flying to the South Pole in a rare and risky mission to rescue a worker in medical distress from a remote research station.

The Twin Otter aircrafts, from Alberta-based airline Kenn Borek Air, were dispatched to the isolated Amundsen-Scott South Pole station because they are designed to endure severe cold and are equipped with skis, allowing them to land in snow, the U.S. National Science Foundation said in a statement.

Officials say the planes could arrive at the research station as early as Sunday, depending on weather conditions. Details of the worker’s medical condition and identity have been withheld to protect their privacy.

But the harsh Antarctic winter – which sees temperatures drop as low as -80 C as darkness blankets the continent – will add a layer of extreme difficulty to the emergency rescue, according to the NSF.

“As there is no tarmac runway at the South Pole, the aircraft must land in total darkness on compacted snow,” the NSF, which runs the research station, said in a press release.

The planes will attempt to reach the ailing worker and bring them “to a hospital that can provide a level of medical care that is unavailable at the station,” the NSF said.

Flying to the South Pole in the midst of winter is exceptionally rare. Flights to and from the research station usually aren’t chartered between February and October “due to the extreme cold and darkness,” the NSF said.

But the Calgary-based airline has experience in these challenging conditions. Kenn Borek Air has made two similar Antarctic evacuation missions before: one in 2001 and another in 2003.

The small propeller-driven planes left Calgary Tuesday on the first leg of the cross-continental journey. They were chartered to arrive in southern Chile and then fly to the U.K.-led Rothera Research Station, located on the northern tip of Antarctica, the NSF said.

From there, one plane will remain in Rothera to provide search-and-rescue capabilities, while the second crew ventures another 2,400 kilometres inland to the Amundsen-Scott South Pole Station.

A pilot who flew in Kenn Borek’s previous two rescue missions said the 10-hour journey from Rothera to Amundsen-Scott will be riddled with challenges, but the crew is getting plenty of support.

“It’s not just Kenn Borek carrying a couple of guys on a Twin Otter. You feel like you’re part of a bigger team project heading down there,” pilot Sean Loutitt told CTV Calgary.

Indeed they are. Due to the mission’s complexity, crews with be working in tandem with several U.S. experts, including weather specialists from the U.S. Navy, medical experts from the University of Texas and a Colorado-based Antarctic logistics contractor.

Limited fuel capacity means the crew will have to work with Antarctic weather forecasters to determine if an ideal “weather window” opens up, and allows them to reach the base, Loutitt said.

“Ultimately, it is the guys in the plane that have to make that decision to continue or not when there’s questionable weather,” he said.

An NSF spokesperson told CTVNews.ca that, as of Sunday afternoon, the two planes remained on the ground in Punta Arenas, Chile.

“They are awaiting favorable weather to fly to the British Antarctic Survey Station at Rothera, where they will prepare the aircraft and await favorable weather to make the flight to the Pole,” NSF spokesperson Peter T. West said in an email.

The Amundsen-Scott South Pole research station is one of three year-round NSF-led operations in Antarctica. According to the agency, 48 people spend the winter in the station studying a wide array of topics, including the atmospheric effects of greenhouse gases, dark matter, black holes and the history of the universe.

Three Canadians from Kenn Borek Air died in 2013 during an Antarctic flight when their plane crashed into a steep slope on the Queen Alexandra mountain range. At the time, the NSF held a memorial at the Amundsen-Scott South Pole Station for the crew, who were flying from the station when the accident occurred.

With files from CTV Calgary