Why does ATC give early descents in flight simulators?

Flight simulator ATC gives early descents because its ATC engine usually calculates a generic vertical profile from the simulator flight plan, not the aircraft’s FMS/VNAV path. Runway or STAR mismatches, altitude restrictions, traffic sequencing and different navigation data can move the clearance earlier. Early permission to descend is not always an instruction to descend immediately.

This applies to general-purpose flight simulators, including Microsoft Flight Simulator 2024, MSFS 2020, X-Plane and Prepar3D, as well as third-party ATC such as BeyondATC. Exact phraseology and available responses vary between ATC systems.

Why does the ATC engine start the descent so early?

The ATC engine and aircraft FMS are often working from different route data and descent assumptions. The ATC engine is the simulator software that generates clearances; it is separate from the FMS or VNAV system flying the aircraft.

A capable airliner FMS can use aircraft weight, speed schedules, entered winds, performance data and procedure constraints to calculate top of descent. Simulator ATC usually works from its own active flight plan and a broader performance model. It may have no access to the detailed vertical path displayed in the cockpit.

A route loaded through the simulator’s planner may feed built-in ATC, while later changes made only through the CDU or avionics remain inside the aircraft. This depends on the aircraft and simulator integration, so changing a runway or STAR in one place does not guarantee that ATC has received it. Our explanation of how built-in flight simulator ATC reads and controls a flight covers that separation in more detail.

An early descent is not automatically bad ATC. A controller may need an aircraft lower for traffic, airspace, a crossing restriction or an arrival sequence. The limitation becomes obvious when the simulator sends the aircraft down early, leaves it level for a long distance and provides no operational reason.

Is the descent clearance actually too early?

The FMS top-of-descent marker is a prediction, not a clearance and not proof that ATC is wrong. Check the required path independently before deciding which system is producing the implausible result.

For a normal three-degree descent, use the planning rule track miles ≈ altitude to lose in thousands of feet × 3. From 35,000 feet to a 3,000-foot restriction, the calculation is (35 − 3) × 3 = 96 NM. That 96 NM is an approximate along-route distance, not an ATC code or instruction.

Use altitudes on the same reference. If the target is 3,000 feet above mean sea level, subtract 3,000 from the present altitude rather than treating it as 3,000 feet above the runway. Add distance for deceleration, level segments and restrictive arrival geometry, and measure along the remaining route rather than directly to the airport.

A related rate check is vertical speed in ft/min ≈ groundspeed × 5. At 450 knots groundspeed, a three-degree path needs about 2,250 ft/min; at 600 knots, it is approximately 3,000 ft/min. Wind changes the time and vertical rate required, while the basic geometric three-to-one distance remains a planning approximation.

The clearance wording then decides when to act:

• Descend and maintain normally requires a prompt descent towards the assigned altitude.
• At pilot’s discretion or when ready generally lets the pilot choose when to leave the present altitude, although regional and simulator phraseology differs.
• Cross a named fix at an altitude gives a defined target and leaves the descent planning to the pilot unless ATC adds another instruction.
• Expect 3,000 feet is advance information. It does not by itself authorise leaving the present altitude.

See our practical explanation of when an immediate, discretionary or crossing-restriction descent should begin if the spoken instruction is ambiguous.

What should I do if built-in ATC or BeyondATC descends way too early?

First establish whether the instruction is merely inefficient or would create a terrain, procedure or approach-stability problem. Use the same checks for built-in ATC and BeyondATC, but remember that they may obtain their routes and navigation data from different sources.

1. Read the clearance literally. Distinguish an immediate descent from permission to descend later, a crossing restriction or an altitude that ATC only says to expect.
2. Compare the active plans. Check the destination runway, STAR, transition, approach and next several legs in both the cockpit and the plan used by ATC. Pay particular attention to changes made after departure.
3. Check the path yourself. Apply the three-to-one calculation, review procedure constraints and confirm that the FMS has not built its path across a discontinuity or duplicate waypoint.
4. Protect the aircraft. Do not follow simulator ATC below terrain-safe altitudes, published procedure minimums or into an approach that cannot be stabilised. Our guidance on handling unsafe simulator clearances explains when to stop treating the ATC engine as authoritative.
5. Choose the appropriate response. If the descent is safe and immediate, comply at a sensible rate even if it is inefficient. If the ATC interface offers a later-descent or higher-altitude request, use it. When built-in ATC has become unusable, cancelling its IFR service and self-managing the published arrival is preferable to chasing contradictory altitudes. With a human controller, request or clarify a different clearance instead of silently ignoring the instruction.
6. Monitor the vertical mode. Lowering the altitude selector does not always start a descent. In many airliners it merely permits or arms VNAV to descend at the calculated point. Select the correct managed or selected mode for the aircraft and monitor thrust, speed, vertical rate and altitude capture.

A mistake we see constantly is assuming that the magenta top-of-descent marker must be correct. It can be displaced by missing wind data, an incorrect cruise altitude, bad constraints or a broken route. Equally, repeated implausible clearances can result from flight-plan mismatches and simplified ATC logic rather than pilot error.

An unnecessarily early descent usually burns more fuel because the aircraft spends longer in denser air. If compliance is required, use a controlled descent rather than diving to the assigned altitude and flying level for many miles. Do not climb back to the previous altitude without another clearance.

Why is MSFS 2024 ATC not telling me to descend?

MSFS 2024 ATC may withhold descent because the flight is VFR, the IFR service or frequency hand-off was interrupted, or the route known to ATC differs from the route and top-of-descent point in the aircraft.

The built-in controller does not simply watch the airliner’s TOD symbol. If the FMS reaches top of descent while ATC believes there are more track miles remaining, it may keep the aircraft at cruise altitude. It can also stop progressing normally after an unacknowledged hand-off or when the avionics contain an arrival that was never passed back to the simulator flight plan.

• Confirm that an IFR clearance, rather than only a VFR plan, is active.
• Check that the latest frequency hand-off was acknowledged and that the next controller was contacted.
• Compare the destination, cruise altitude, runway and arrival in the simulator’s active plan with the aircraft FMS.
• Look for an available request for a lower altitude or descent; response choices depend on the stage of flight and ATC system.
• If built-in ATC remains silent beyond a sensible descent point, avoid creating an unstable arrival. Where available, cancel the simulated IFR service and fly the planned vertical profile, or correct and reload the route.

That last option applies only to scripted simulator ATC. Under human online control, remain at the cleared altitude and ask for descent.

Can airliners fly VFR in MSFS 2024 or another ATC sim?

Yes. An airliner can be flown under VFR in a flight simulator because aircraft size does not by itself determine the flight rules, although real scheduled airline operations are normally conducted under IFR and legal requirements vary by jurisdiction and operation.

With a VFR plan, in-flight ATC may provide traffic information, controlled-airspace services and airport instructions, but you should not expect an IFR-style STAR descent or assigned step-down profile. If you want ATC to control the airliner’s descent and approach, submit and activate an IFR plan.

If “ATC 24” refers to a separate ATC game, scenario or multiplayer server rather than MSFS 2024 ATC, its own rules may prohibit VFR airliners. Follow that simulation’s rulebook; the general aviation principle does not override server or scenario restrictions.

How can I prevent repeated early ATC descents?

The most reliable prevention is to give the ATC engine and aircraft the same route before departure, then update both after every runway or procedure change.

• Match the complete route: origin, destination, cruise altitude, runway, STAR, transition and approach.
• Inspect the vertical constraints: do not delete genuine restrictions merely to make the FMS and ATC agree.
• Resolve route defects: remove accidental duplicate fixes and deal with discontinuities before descent.
• Recheck after changes: a runway change made only in the CDU is a common cause of bad in-flight ATC instructions.
• Keep navigation data compatible: disagreement over fix positions or procedure altitudes can produce different descent points even when the route names look identical.
• Recognise an engine limitation: if the same unreasonable step-down occurs on unrelated routes with synchronised plans, the ATC model is the likely cause. Another ATC system or a self-managed arrival may behave better, but third-party ATC can also suffer from route and data mismatches.