Busy or physically constrained airports meter their traffic with slots — a reserved window, often 15–60 minutes wide, for each arrival and departure — or with PPR, "prior permission required," where every movement needs individual approval from the airport authority. Slots ration runway and airspace capacity; PPR usually rations ramp parking. Classic slot or PPR airports in the charter world include Aspen and the Colorado mountain fields, London City and the London-area business airports at peak times, Nice in summer, and almost any airport near a major event — Las Vegas during F1 or a Super Bowl city operates under temporary slot programs that make ordinary days look easy.
Mechanically, the operator's dispatch team requests slots once your trip is confirmed, and the airport assigns what's available. On a normal Tuesday this is invisible. On a constrained day the slot becomes the schedule: you depart when the slot says, not when you'd prefer, and the popular windows — Friday afternoon into a ski town, Sunday afternoon out — fill days or weeks ahead. Compliance is tight: miss your window and the aircraft may hold, wait hours for the next opening, or divert. Event-period PPR often comes bundled with mandatory handling and parking reservations that can run into thousands of dollars for the weekend, and some airports simply run out of ramp — the aircraft drops you and repositions to park elsewhere, adding two ferry hops to your invoice.
For the customer, slots explain two frustrations that otherwise look like operator inflexibility. "Can we push departure an hour?" is trivial at an uncontrolled field and sometimes impossible at Aspen on a Saturday — the slot you hold may be the only one left. And a cheap-looking quote into a constrained airport may not include event parking, PPR fees, or the repositioning-to-park problem, so ask specifically what happens to the aircraft on the ground. Booking early matters more here than anywhere else in charter: aircraft supply and slot supply collapse together on peak days, and the traveler who committed three weeks out gets both the jet and the window.
Two clarifications. Slots at business airports are operational, day-of-flight reservations — not the traded, grandfathered slot rights airlines hold at Heathrow, which is a different system sharing the name. And PPR is not a formality that dispatch can always solve: at small mountain or island fields, a full ramp is a hard no, and the practical answer becomes the alternate airport — Rifle or Eagle instead of Aspen — which is often the better trip anyway.
