In this study, four distinct approaches for flight frequency regulation are investigated with the objective to mitigate network congestion. The approaches differ in the way how a specific number of daily flights on a route is determined: (1) directly regulating the number of flights, (2) defining an average air traffic flow management (ATFM) delay target, (3) setting a minimum acceptable schedule delay or (4) based on the marginal temporal utility of a frequency. All frequency regulation approaches are mathematically modelled, algorithmically implemented and applied to the 798 top routes by frequency in the EUROCONTROL area for the timeframe from 2020 until 2040. It is investigated that 7.6–22.3 million ATFM delay minutes could be avoided in 2040, depending on the chosen frequency regulation approach. This corresponds to a decrease in average ATFM delay per flight of 10%–27% whereas only 2%–3% of flights are reduced. If it is conservatively assumed that non-plannable ATFM delay creates twice as much temporal disutility as plannable schedule delay, the ATFM delay decline compensates the schedule delay increase due to fewer frequencies for all regulation approaches from 2035 on. To keep seat capacity constant, airlines would have to increase average aircraft sizes considerably on frequency-reduced routes making the deployment of twin-aisle aircraft necessary. Operation-, environment-, market- and regulation-related implications are discussed.
