A member of the U.S. Antarctic Program was rescued from Antarctica’s McMurdo Station last week because of an unspecified medical issue.

While flights to the region are common during the Southern Hemisphere summer, this mission took place during the dark, frigid winter.

An Airbus A319 landed at the station’s adjacent airfield. The Australian Antarctic Division said temperatures dropped to about minus 45 degrees Fahrenheit when the flight landed in darkness.

The patient was transported to Christchurch, New Zealand, for medical treatment.

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“This was a complex operation carried out in the depths of the Antarctic winter, and it highlights both the capability of our people and the strong partnerships that underpin Antarctic programs around the world,” Australian Antarctic Division head Emma Campbell said.

This was not the first risky winter rescue at the station. Last year, one person needed urgent medical care, while two others required less urgent treatment.

“Although they determine it is safe, it’s still an extremely challenging environment to fly in on night vision goggles because of the extreme weather conditions, which are highly changeable at this time of year and make accurate forecasting a challenge,” New Zealand Air Component Commander Air Commodore Andy Scott said.

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McMurdo Station generally has a population of about 1,200 to 1,400 during the summer, but that number shrinks to about 200 in the winter.

McMurdo Station is about 850 miles from the South Pole.