A departure sequencing system models airport operations and provides suggested gate pushback times for aircraft. In various embodiments, a departure sequencing system includes an airport state analyzer, a taxi-out predictor, and a pushback optimizer. The departure sequencing system may utilize stochastic models, and resolve aircraft conflicts using a business rules engine. Via use of the departure sequencing system, taxi times may be reduced, taxi fuel burn may be reduced, and airport throughput may be increased.