Flight times are determined by a complex interplay of distance, wind speed, aircraft performance, and air traffic control (ATC) routing. The most significant variable is the jet stream; a strong tailwind can shave an hour off a transatlantic flight, while a headwind can add just as much time. This is why flying from New York to London is usually faster than the return trip. Additionally, pilots must follow specific "highways in the sky" or airways dictated by ATC, which are rarely a perfectly straight line due to weather, restricted military airspace, or "no-fly zones." The aircraft's cruising speed (Mach number) and weight also play a role, as heavier planes may need to fly at lower, less fuel-efficient altitudes initially. In 2026, airlines also use "block time" to schedule flights, which includes a buffer for taxiing, de-icing, and potential airport congestion. This is why a flight might be listed as 3 hours even if the actual time in the air is only 2 hours and 20 minutes; the airline is padding the schedule to ensure on-time arrivals.