1. A method of estimating, in real time, the amount of any delay, from a planned departure time, in departure of an aircraft flight from an airport, the aircraft belonging to a fleet, the flight associated with a departure airport and an arrival airport, the method comprising: a. receiving in a first computer process a conditions input that includes at least one member of a set including departure airport conditions, arrival airport conditions, and fleet conditions; and b. estimating in a second computer process the amount of delay based on the conditions input.