The condition is that one of the following happened to you:
Your flight is delayed for more than 3 hours
Your flight is cancelled
Your flight is delayed for less than 3 hours, but you miss a connection flight and arrive to your final destination more than 3 hours late
You were denied boarding because of lack of vacant seats (overbooking)
The flight must not be delayed due to weather or other extraordinary conditions.
The flight must have been commenced no later than 6 years ago.