How accurate is flight time in a flight simulator?

In a home flight simulator, airborne flight time can match a real flight to within a few minutes when the aircraft, route, winds, weight and speed profile are matched and the sim runs at normal rate. Gate-to-gate time is less predictable because real taxiing, ATC vectors, holding and schedule padding vary.

Which flight time should you compare?

Airborne time from lift-off to touchdown is the cleanest comparison. Different clocks start and stop at different points, so two apparently conflicting durations may both be correct.

A mistake we see constantly is comparing an airline's advertised gate-to-gate duration with a simulator timer started on the runway. A simulated flight can be 20 minutes shorter without the aircraft flying unrealistically fast.

There is no universal acceptable error. Use a percentage as well as minutes: five minutes is significant on a 30-minute hop but negligible on a ten-hour flight. Matching the duration also does not prove that fuel burn, handling or aerodynamics are accurate; several errors can cancel each other out.

Why does simulator flight time differ from a real flight?

Most differences come from mismatched routing, wind, speed or timing definitions rather than an inaccurate simulator clock.

• Route distance: The same airports do not guarantee the same distance. Runway choice, SIDs, STARs, airway restrictions, shortcuts and radar vectors can add or remove many nautical miles.
• Winds aloft: Flight duration follows groundspeed, not indicated airspeed or Mach alone. A strong headwind can materially extend a flight even when the aircraft maintains the correct cruise setting.
• Aircraft configuration: The exact variant, engine type, payload, fuel load and cruise altitude affect climb rate, optimum altitude and speed. A basic aircraft model may not reproduce the real performance schedule closely.
• Operating technique: Cost index, climb speed, cruise Mach, step climbs, descent profile and speed restrictions all alter elapsed time. Simply engaging maximum cruise speed is not a fair airline comparison.
• ATC and traffic: Real flights receive vectors, holds, shortcuts and runway changes that cannot be predicted from the published route alone.
• Ground operations: Pushback, de-icing, runway queues and long taxi routes affect block time but not airborne time.
• Simulation controls: Pause, slew, repositioning and simulation-rate changes invalidate a wall-clock comparison. Under heavy processing load, some simulators can also let simulated time drift relative to a real clock.

Even two real services with the same flight number can have different times on consecutive days. Comparing one simulator flight with one unrelated real-world result is therefore weak evidence unless the date, route and weather also match.

How do you compare simulator and real flight time fairly?

A fair test reproduces one real flight's conditions and compares like-for-like timestamps.

1. Choose the reference measurement. For aircraft and route accuracy, record the real flight's OFF and ON times. Use OUT and IN only when testing the complete gate-to-gate operation.
2. Identify the exact aircraft. Match the variant and engines where possible. A livery showing the correct airline does not mean the underlying model is correct.
3. Recreate the route. Match the departure runway, arrival runway, SID, airway route and STAR rather than flying directly between airports. Our guide to finding a suitable real-world simulator route explains what route data to reproduce.
4. Match the flight plan. Enter realistic payload, fuel, cruise level and speed or cost index. Dispatch-style planning for route, loading and fuel gives a better estimate than dividing the direct distance by maximum cruise speed.
5. Match the atmosphere. Use winds and temperatures from the flight's date and time. Live weather is only a valid match for a flight happening under the same conditions; using today's weather to recreate an older flight can produce a large difference. We explain the available options in our guide to configuring real-time simulator weather.
6. Fly at normal simulation rate. Follow the planned climb, cruise and descent speeds without pausing, slewing or repositioning.
7. Record checkpoints. Note UTC at take-off, top of climb, top of descent and touchdown. This shows where the difference developed instead of leaving one unexplained total.

If the discrepancy appears before top of climb, inspect weight, temperature and climb schedule. A difference accumulated in cruise usually points to wind, routing, altitude or cruise speed. Time gained or lost after top of descent commonly comes from the STAR, vectors and speed restrictions.

Distance divided by groundspeed is useful only as a rough check. For example, a 600 NM segment at an average groundspeed of 400 knots takes 1.5 hours, but a complete flight also contains climb, descent and routing changes.

Does time acceleration invalidate the comparison?

Yes, time acceleration invalidates a real wall-clock comparison and may also reduce the accuracy of the simulated operation. The in-simulator clock may advance proportionally, but autopilots, traffic, weather updates and waypoint sequencing do not always behave identically at high simulation rates.

For a timing test, use normal rate and verify that one hour of simulated UTC equals one hour on a real clock. If the aim is simply to shorten a long cruise rather than measure accuracy, our explanation of simulation-rate controls and their limitations covers the safer options.

When a simulator flight appears much shorter than the airline schedule, compare OFF-to-ON times before changing the aircraft's speed. In most cases, the missing time is taxiing, operational padding, a different route or different winds—not a fast simulator clock.