Employing primary and secondary data, a European, aggregate ‘hard’ cost model is developed for the airline cost of passenger delay. These costs are then newly modelled as a function of delay duration, quantifying how longer delays have higher per-minute costs. Passenger ‘hard’ plus ‘soft’ costs of delay typically dominate other delay costs (e.g. associated with crew and maintenance). Integrating disruption management techniques into flight planning presents major cost-saving opportunities. A shift in air traffic management strategy from managing delay minutes to delay costs, including those of emissions, is required if true 4D/‘business’ trajectories are to be realised.