Cancelled flight compensation is not valid if the flight was cancelled because of extraordinary circumstances or other disruptions not related to airline actions. For example, strikes, political unrest, bad weather conditions (such as, snow, wind, fog, storm etc.), airport operation failures, airplane manufacturing errors, birds flying into the engine etc. What is more, your flight cancellation compensation may be reduced if you have received other facilities from airlines in form of compensation, such as discount and gift vouchers. In fact, your flight arrival must be more than 3 hours later than it was planned in order to receive compensation. You will find more information in Air Passenger Rights.