Ryanair is an ultra-low-cost airline primarily based out of Dublin and London Stansted airports. It is the busiest passenger airline in Europe. Ryanair operates a fleet exclusively comprised of B737 variants, and has an average fleet age of roughly 7 years. It has often been accused of providing poor customer service, and generates significant revenue from extra charges and surcharges. Ryanair does not have a frequent flier program, and is not a member of any recognised alliance.