UPDATE: June 22, 2016, 11:06 a.m. EDT The rescue plane has left the South Pole with one patient aboard, and is flying the 10-hour flight back to the British Antarctic Survey's Rothera Base on the Antarctic Peninsula.

Update: South Pole Medical evacuation flight, #Antarctic June 22: Plane has left the Pole: https://t.co/mSnqcStEc1 pic.twitter.com/mtkMzYsDpG — NSF Polar Programs (@NSF_OPP) June 22, 2016

UPDATE: June 21, 2016, 6:07 p.m. EDT After a 10-hour flight through the frigid Antarctic winter night, a small propellor plane has landed at the South Pole. The National Science Foundation said the plane will rescue one, or possibly two, contractors for the agency who need medical treatment that is beyond the Amundsen-Scott South Pole Station's capability. This is only the third time that a wintertime rescue mission has been attempted.



The pilots will now rest for several hours and the plane will be refueled before waiting for a window of favorable weather conditions. The plane will then fly another 10-hour flight back to a British base on the Antarctic Peninsula, and from there to South America.

UPDATE: June 21, 2016, 12:19 p.m. EDT A rescue plane is now in the air on its way to the Amundsen-Scott South Pole Station in order to rescue at least one sick contractor for the National Science Foundation (NSF). The plane left the British Antarctic Survey's Rothera Base on Tuesday morning local time, and is expected to arrive at the South Pole at about 5 p.m. ET, the NSF stated in a press release. "The aircrew took advantage of a favorable weather window to leave," the press release states. The current temperature at the South Pole Station is a brutal minus-72 degrees Fahrenheit, with mostly clear skies. Our original story is below:

A rare, daring mission is underway in Antarctica to rescue an ill contractor for the National Science Foundation from the frigid, isolated and dark Amundsen-Scott South Pole Station.

Right now, two propellor-driven DeHavilland Twin Otter aircraft are on the ground at the British Antarctic Survey's Rothera base, located on the Antarctic Peninsula.

Once a window of favorable weather conditions appears, one of the planes will fly south in complete darkness and extreme cold, to the South Pole Station. The other plane will remain at Rothera, ready to launch a rescue mission should the first plane go down.

According to a statement from the National Science Foundation (NSF), which operates the South Pole Station, at least one member out of the 48 overwintering crew will be evacuated to receive medical treatment.

That crew member is a contractor for Lockheed Martin Antarctic Support, which is the main support contractor to NSF for the U.S. Antarctic Program.

"It is possible that the evacuation flight will bring a second patient out of Antarctica. That decision still is pending," the NSF stated in a press release Monday. The agency did not release any details about the patients or the nature of their illnesses.

This is only the third time that a rescue attempt has been launched for an ill crew member at the South Pole during the Antarctic winter. The most recent such medical evacuation was in 2003.

A Twin Otter aircraft arrives at the NSF's Amundsen-Scott South Pole Station To Provide Medical Supplies on April 24, 2001. Image: Getty Images

Typically, crew members at the South Pole are inaccessible during the winter until the spring season begins in October. Crews live at the center to keep experiments and atmospheric measuring equipment running until the spring arrives and aircraft can fly supplies and new crew members to the pole.

The NSF decided to order the mission in light of a medical condition that cannot be adequately treated at the infirmary on the South Pole outpost.

The NSF contracts with Kenn Borek Air, Limited of Canada to provide logistical support to the Antarctic program. The company dispatched two Twin Otters from Calgary, with crews that flew them south over the span of several days, across the U.S., Mexico, Central America and South America, all the way to Punta Arenas, Chile.

From there, the planes flew over the stormy Southern Ocean to Rothera, from where the rescue mission will be launched.

There are 48 people wintering at the Amundsen-Scott South Pole Station, according to the NSF. It is one of three year-round facilities the agency operates on the continent.

The landing area is prepared at the NSF's Amundsen-Scott South Pole Station in 2001 prior to a medical rescue mission. Image: Getty Images

The station pursues scientific projects such as monitoring atmospheric carbon dioxide, conducting radio telescope observations and observing subatomic particles produced by black holes and other phenomena.

Why the small propellor planes?

One might think the rescue mission would be carried out by a military cargo aircraft, such as a Boeing C-17 Globe Master or C-130 Hercules.

However, both those aircraft are not certified to fly in the extreme cold encountered in the atmosphere above the South Pole, with the cold potentially freezing fuel lines and hydraulic fluid, said Peter West, a spokesman for NSF's polar programs office.

At the end of the day, we are balancing the health and safety of the flight crew and the health and safety of the patient

The Twin Otters, on the other hand, were designed by a Canadian manufacturer with cold weather in mind. They lack complex systems that could freeze up, and are ideal for landing on short, snow-covered makeshift runways. For the mission, these Twin Otters will be outfitted with skis in order to land on snow.

According to West, a crew of four people will make a 3,000-mile round trip flight from Rothera to the South Pole and back: two pilots, a mechanic and a medical technician. The round-trip flight is likely to take about 20 hours, West told Mashable.

"At the end of the day, we are balancing the health and safety of the flight crew and the health and safety of the patient,” West said.

Kenn Borek Air carried out two other similar medical evacuation flights from the South Pole, one in 2001 and the other in 2003.

As of Monday afternoon eastern time, the temperature at the South Pole was minus-58 degrees Fahrenheit, with a wind chill of minus-92 degrees.