Every year, there are a number of Kenn Borek planes, mostly Twin Otters, that need to be moved from the Arctic to the Antarctic and back. These planes mainly work out of McMurdo Station during the Austral summer, but McMurdo is far enough from the nearest civilisation (New Zealand) that the planes can't fly directly (nevermind that getting to NZ from Canada would be an epic by itself).
So, they fly the length of the Americas, hop over to the Antarctic Peninsula, and cross the continent over South Pole, to get to McMurdo. This all happens at about the earliest and latest in the summer when the planes can fly, so that puts them going through some pretty marginal conditions at South Pole in particular.
It's also very important that the crews bring "freshies" from South America or they may not be allowed in to the station at South Pole, where they're the first outsiders in ~9 months.
As for the crossing from NZ-Antarctica, even large planes struggle, there's generally a point in the journey that they have to commit to landing as they don't have enough fuel to get there, abort and come back. This can be an issue as the weather in Antartica changes rapidly so you may find yourself in a storm after getting the green light to commit, as the RNZAF 757 did a few years ago:
Impressive as they are, the last(final?) time the C-5 came to Christchurch the C-17s looked ordinary next to them.
When the C-5 was lined up, the taxing A320's looked like dinkys.
However, the C-5 was to big to head down to the ice.
So, they fly the length of the Americas, hop over to the Antarctic Peninsula, and cross the continent over South Pole, to get to McMurdo. This all happens at about the earliest and latest in the summer when the planes can fly, so that puts them going through some pretty marginal conditions at South Pole in particular.
It's also very important that the crews bring "freshies" from South America or they may not be allowed in to the station at South Pole, where they're the first outsiders in ~9 months.