Under this rule, airlines must use at least 80% of their take-off and landing slots at European airports or face losing them to a competitor the following year.

In the airline industry, the 80/20 rule (or "Use it or Lose it" rule) refers to the mandatory utilization of airport slots. To maintain their "historic rights" to a specific takeoff or landing slot for the next season, an airline must use that slot at least 80% of the time. If they fail to meet this threshold, the slot can be taken away and re-auctioned to a competitor. This rule is designed to prevent airlines from "sitting" on valuable slots at congested hubs like London Heathrow or New York JFK just to block rivals. While temporary waivers were common in the early 2020s due to global travel disruptions, 2026 sees the strict 80/20 standard fully reinstated. This creates "ghost flights" in some cases, where airlines fly empty planes just to preserve their slot ownership, though newer 2026 sustainability mandates are putting pressure on this practice to be more flexible.