Definition

The accident rate is defined as the ratio between the number of accidents which happened in a given year and the number of flights conducted during that same year. The accident rate gives an estimate of the accident risk per flight. It is generally expressed in accidents per million flights.
The accident rate can be calculated for any set of States like ICAO regions, civil aviation committees or the whole world. When applied to a set of States other than the world, ICAO estimates the number of flights by twice the number of departures in that set of States which is the most favourable situation in terms of accident rate.