Complex sentence: London Heathrow airport is the largest airport in the country, handling over 67 million terminal passengers in 2006, making it the third busiest airport in the world, and the busiest if measured by the number of international passengers.
Split into simpler sentences: London Heathrow airport, handling over 67 million terminal passengers in 2006, being the largest. By this metric Heathrow is the third busiest airport in the world, and the busiest if measured by the number of international passengers.