A plane carrying two ailing passengers from the South Pole arrives safely in Chile late Wednesday, according to a statement from the National Science Foundation.

The American workers arrived in the southern Chilean city of Punta Arenas. They made a stop earlier at a British station on the edge of Antarctica.

The National Science Foundation, which runs the Amundsen-Scott station, would not identify the workers, who are employees of Lockheed Martin, nor their medical conditions.

The foundation said initially that one worker needed medical attention, but NSF spokesman Peter West confirmed two people were airlifted. Normally planes don't use the polar outpost from February to October because of the dangers of flying in the pitch dark and cold.

The Twin Otter's crew -- a pilot, co-pilot, flight engineer and medical worker -- arrived at the frigid research station Tuesday before resting for several hours as temperatures dropped below minus 70 degrees.

Before they left, there were 48 people — 39 men and nine women — at the station for the winter.

Steve Barnet, who works with a University of Wisconsin astronomy team at the polar station but is in the U.S., now, lauded the rescue crew.

"The courage of the pilots to make the flight in extremely harsh conditions is incredible and inspiring," Barnet wrote in an email.

The extreme cold affects a lot of things on planes, including fuel, which needs to be warmed before takeoff, batteries and hydraulics, according to West. The Twin Otter can fly in temperatures as low as minus 103 degrees (minus 75 degrees Celsius), he said.

"The air and Antarctica are unforgiving environments and punishes any slackness very hard," said Tim Stockings, operations director for the British Antarctic Survey. "If you are complacent it will bite you."

"Things can change very quickly down there" with ice from clouds, high winds and snow, he said.

There have been three emergency evacuations from the Amundsen-Scott station since 1999. That first flight, which was done in Antarctic spring with slightly better conditions, rescued the station's doctor, Jerri Nielsen, who had breast cancer and had been treating herself. Rescues were done in 2001 and 2003, both for gallbladder problems.

Scientists have had a station at the South Pole since 1956. It does astronomy, physics and environmental science with telescopes, seismographs and instruments that monitor the atmosphere. The foundation runs two other science stations in Antarctica.

Fox News’ Greg Palkot and the Associated Press contributed to this report.