HUSH UP The secret airline you won't have heard of - and destinations are classified RYANAIR, easyJet and British Airways are some of the most popular airlines used by Brits heading on a well-deserved holiday abroad. But there is one airline you won’t have heard of – and is known for being one of the most secretive in the world. 4 A secret airlines known as Janet is one you won’t have heard of Credit: Getty 4 The airline operates from Las Vegas airport Credit: Alamy 4 it mainly carries government officials between Las Vegas and Area 51 Credit: Getty…