HHow do you become a millionaire?

Start with a billion pounds and then start an airline.

Sir Richard Branson's joke about Virgin Atlantic's fame and fortune somehow illustrates how difficult it is to run a profitable airline.

Between oil prices, delays and disruptions and a fiercely contested market, air traffic may seem big business, but it is notoriously difficult.

That said, it's not all that costs a living. New analysis by aviation experts OAG has highlighted the specific routes that some of the world's largest airlines are making their money on – and that's a lot of money.