Air Australia

Air Australia was an airline which serviced at least Heathrow Airport. On the day that the Fifth Doctor, Nyssa and Tegan landed at Heathrow — immediately following Adric's death — the airline had to temporarily suspend operations due to inclement weather. (TV: Time-Flight)

Behind the scenes
Though there has been an in real life, it did not exist until the 21st century, which means that this Air Australia must be regarded as wholly fictional.