  Variation and imbalance in demand poses significant challenges to Urban Air
Mobility (UAM) operations, affecting strategic decisions such as fleet sizing.
To study the implications of demand variation on UAM fleet operations, we
propose a stochastic passenger arrival time generation model that uses
real-world data to infer demand distributions, and two integer programs that
compute the zero-spill fleet size and the spill-minimizing flight schedules and
charging policies, respectively. Our numerical experiment on a two-vertiport
network shows that spill in relatively inelastic to fleet size and that the
driving factor behind spill is the imbalance in demand.
