Two sick workers were evacuated from the National Science Foundation's (NSF’s) Amundsen-Scott South Pole research station today and taken to the British Antarctic Survey’s Rothera station on the Antarctic Peninsula. They are now awaiting transport off the continent to receive medical care, either today or tomorrow, depending on weather conditions. NSF is not releasing the workers’ identities and medical conditions, citing privacy.

Here is our previous coverage, from 15 June:

Two propeller-driven planes took off today from Calgary, Canada, on a perilous rescue mission to the U.S. research station at the South Pole. If all goes well, one of the planes will arrive in 6 days to pick up a member of the winter-over crew suffering from an unspecified medical emergency that requires treatment at a hospital.

Every February, after the scientists have left, a few dozen people hunker down to spend the long, dark austral winter at the Amundsen–Scott South Pole research station operated by the National Science Foundation (NSF). Medical problems do occur, but most can be handled with medical personnel on site or in consultations with stateside doctors. The decision to evacuate someone is not made lightly because such a rescue operation is both dangerous and elaborate. Medevacs require planes that can operate in the extreme cold and are equipped with skis. The South Pole station has no tarmac, so the planes must land in the dark on compact snow.

The Twin Otter aircraft are operated by the Canadian firm Kenn Borek Air, Ltd., which contracts with NSF to provide logistical support to the U.S. Antarctic Program. The aircraft will fly via South America to the British Antarctic Survey’s Rothera Research Station on the Antarctic Peninsula. One will remain there as a backup for search-and-rescue operations; the other will travel another 2400 kilometers to the South Pole.

The planes are based year-round in Canada because they are used during the summer months to transport scientists working in the Arctic, says Kelly Falkner, head of NSF’s Division of Polar Programs in Arlington, Virginia. NSF doesn’t own its own aircraft, and “the program’s demand for the planes is almost nil” during the austral winter, she says. In recent decades, Kenn Borek’s Twin Otters have conducted perhaps a handful of emergency rescues.

The plight of overwintering researchers garnered national attention in 1999, when South Pole physician Jerri Nielsen learned she had breast cancer in late May. The only medical professional on hand, she enlisted untrained technicians to help her perform a biopsy and remained on station until her evacuation in October. And in August 2011, when 58-year-old Renee-Nicole Douceur, winter manager at the station, suffered a stroke, NSF deemed it unsafe to send in a rescue plane. Despite pleas from family members, a petition to the White House, and numerous media stories, Douceur remained at the South Pole for 2 months until she finally caught a ride out on a scheduled cargo plane.

NSF officials have not identified or released any information about the medical condition of the crew member, who is employed by Lockheed Martin Antarctic Support Contract (ASC). ASC is the prime contract for operations and research support contractor to NSF for the U.S. Antarctic Program.

*Update, 15 June, 4:47 p.m.: You can track the progress of the rescue mission here.