How long can an airline delay a flight before they have to cancel it?

There's no federal law that forces an airline to cancel a flight after a certain delay length. Airlines can delay a flight indefinitely — 2 hours, 5 hours, 12 hours — without ever technically cancelling it. This is a deliberate strategy: a cancelled flight triggers automatic refund rights, while a delayed flight keeps passengers waiting with fewer options.

What does kick in at specific thresholds: under the DOT's 2026 rule, a domestic delay of 3+ hours or an international delay of 6+ hours counts as a "significant change" that entitles you to a full cash refund if you choose not to fly. You don't have to wait for the airline to cancel — you can declare yourself done and demand your money back.

The 3-hour tarmac rule (14 CFR 259.4) is separate: airlines must give you the option to deplane after 3 hours on the tarmac for domestic flights (4 hours international). But this only applies to sitting on the runway, not gate delays.

Practical advice: if your flight is delayed 3+ hours domestic, don't wait for a cancellation announcement. Go to the counter, cite the DOT significant delay rule, and request either rebooking or a full refund. The airline must comply — cash, not vouchers.