A Calgary-based team has arrived in Chile after rescuing two people in need of medical attention from an Antarctic research facility at the South Pole.

See their daring rescue route in a graphic timeline at the bottom of this story

The crew landed safely at the British Antarctic Survey's Rothera Research Station after leaving the South Pole early Wednesday morning, according to the U.S. National Science Foundation (NSF).

The pair was not treated at Rothera, NSF spokesman Peter West told CBC News from Arlington, Va.

West would not release any information on the patients' condition or treatment, but said they would not have been airlifted out if their condition did not merit it.

West said the pair, along with the Twin Otter flight crew, had to make a difficult 10-hour journey to Rothera in a small airplane in cold, dark and dangerous conditions. A medical technician was on board, he said.

A second Twin Otter took the pair to Punta Arenas in Chile, said Paul Seagrove at the British Antarctic Survey, which operates the research base in Rothera.

"The operation is going according to plan," he added.

After leaving Calgary June 14, the crew arrived at the Amundsen-Scott South Pole Station on Tuesday afternoon and rested for 10 hours before beginning their return journey with two of the 48 people stationed there.

The Twin Otter operated by Calgary's Kenn Borek Air made the 2,400-kilometre, nine-hour trip on Tuesday from the British base on the Antarctic Peninsula.

It's midwinter in Antarctica, and the foundation said flights in and out of the station are usually not planned between February and October due to the extreme cold and darkness.

The foundation said the planes that Kenn Borek Air flies are able to operate in extremely low temperatures and can land on skis. Because there is no tarmac runway at the South Pole, it said the aircraft must land in total darkness on compacted snow.

Kenn Borek provides contractual logistical support to the Antarctic program, according to the foundation, and conducted similar evacuations in 2001 and 2003 — the only other times a winter rescue flight has been attempted in the 60-year history of the station.

At Rothera, the aircrews prepared the planes, including equipping them with skis for a landing on snow and ice at the pole.

One plane flew to the pole for the medical mission, while the other remained at Rothera to provide search-and-rescue capability, if needed.

'Big challenge'

The director of operations at the British Antarctic Survey says it's a complex mission.

"It is a big challenge," Tim Stockings told CBC News from London.

"You have to consider the weather, you have to consider the fuel and I don't know what it's like where you are now but in Antarctica the weather can change minute by minute … it is the sort of thing we do day in and day out but in the middle of winter, as you'll understand, it's just that little bit more challenging."

Stockings says the next steps are about getting the passengers to a safe place.

"Obviously we'll do our best to make sure that we look after the crew in the aircraft but our main aim is to help the crew to get their passengers back to a place where they can be properly looked after as quick as we can."