Good Lawyer Guide's response

You are entitled to compensation if your flight is delayed for more than three hours (ie if you reach your destination more than three hours after the original scheduled arrival time).

There is an exception if the airline can show that the delay or cancellation was caused by ‘extraordinary circumstances’. There is much argument about what that phrase means (in particular, there has been confusion about whether technical faults are covered).

It is only recently that the European Court of Justice has held that passengers are entitled to compensation for flights delayed for more than three hours. Previously, there was no entitlement to compensation (just free drinks, meals and two phone calls).