The twin otter doesn't have enough range to fly from Cape Town to Troll research base. That's why they use the 767-300ER. They do use the twin otter for intern

The twin otter doesn't have enough range to fly from Cape Town to Troll research base. That's why they use the 767-300ER. They do use the twin otter for internal flights, but they have to be ferried down via south america (without passengers)