London's Heathrow, shut down by a power outage, is Europe's busiest airport - but only the 4th or 5th globally. Here's a look at the world's busiest airports.

London’s Heathrow Airport shut down because of a power outage from a large fire nearby, causing massive disruption at one of the world’s busiest travel hubs. The disruption is causing havoc for hundreds of thousands of travelers and having ripple effects worldwide.