FS2004 overspeed warning at every altitude? Understand IAS, Mach, the barber pole, 400 kts, autopilot targets and aircraft.cfg limits.
FS2004 (FS9) shows an overspeed warning when an aircraft exceeds either its configured maximum indicated airspeed or maximum Mach number; the active limit is whichever is reached first. IAS usually controls lower down, while Mach controls aloft. Reduce thrust and remain below the moving red-and-white barber pole.
Which speed triggers the FS2004 overspeed warning?
FS2004 uses indicated airspeed and Mach for overspeed protection, not true airspeed or GPS groundspeed. With a standard panel, the relevant limits come from the aircraft's configuration; some add-on gauges apply their own warning thresholds as well.
| Speed | What it measures | Can trigger overspeed? |
|---|---|---|
| IAS or KIAS | Airspeed shown on the primary flight instrument | Yes; normally the controlling limit at lower altitudes |
| Mach | Speed relative to the local speed of sound | Yes; commonly the controlling limit in high-altitude cruise |
| TAS or KTAS | Actual speed through the surrounding air mass | No, not directly |
| GPS groundspeed | Speed across the ground, including wind effect | No |
The red-and-white barber pole on the airspeed indicator represents the maximum permissible speed. In a correctly modelled jet panel, it moves down the IAS scale as the Mach limit becomes restrictive.
Will 400 kts trigger the warning?
At 400 kts, the answer depends on which kind of speed is being displayed. 400 KIAS exceeds the maximum indicated speed of many jet transports and is likely to trigger an overspeed warning; at altitude it may also exceed the aircraft's maximum Mach number.
By contrast, 400 KTAS or 400 knots of GPS groundspeed can be normal for a jet whose indicated airspeed remains safely below the barber pole. Our explanation of why indicated airspeed and GPS groundspeed disagree shows why a high ground-speed figure is not itself an overspeed.
Why can the listed cruise speed be unsafe in IAS mode?
A stated cruise speed is often TAS or Mach, not a value to enter directly into the IAS selector. Setting an autothrottle to 400 knots IAS because the aircraft is described as cruising at about 400 knots is a common cause of repeated warnings.
The cruise_speed reference in an aircraft's configuration does not override its maximum IAS or Mach limits. Follow the aircraft's IAS-to-Mach climb schedule, or keep the selected speed comfortably below the barber pole if no schedule is supplied.
Why does the Mach airspeed warning start at a lower IAS aloft?
The Mach airspeed warning begins at a lower indicated speed aloft because the aircraft reaches its maximum Mach number before reaching its maximum indicated airspeed. This is expected behaviour, not an FS2004 altitude fault.
As an aircraft climbs, a given IAS represents a progressively higher Mach number. At the crossover altitude, the Mach limit becomes more restrictive than the IAS limit, so the barber pole moves down the indicated-speed scale. This explains why a speed that is acceptable lower down can produce an overspeed warning in the cruise.
If the panel offers separate IAS and Mach modes, change to the appropriate Mach target during the climb rather than carrying a high IAS selection to cruise altitude. If the aircraft keeps accelerating, changes the target unexpectedly or will not obey the selected mode, work through our FS2004 autopilot and autothrottle checks.
How do I clear an overspeed warning in FS2004?
Reduce the aircraft's energy smoothly until both IAS and Mach are below their limits; merely changing altitude will not silence a genuine overspeed.
- Check both IAS and Mach. A modest-looking indicated speed may still be above the Mach limit at high altitude.
- Correct the selected speed. Lower the IAS or Mach target and disconnect the autothrottle or autopilot if it continues to command acceleration.
- Reduce thrust and control the descent. Level off or reduce the descent rate if safe. Use speed brakes only within the aircraft's operating limits.
- Wait for the speed to decay. Throttling back does not clear the alert instantly because the aircraft still carries excess energy.
- Leave a margin below the barber pole. Turbulence, instrument rounding and small autopilot corrections can repeatedly cross the limit when flying exactly on it.
- Do not use gear or flaps as emergency brakes. They have separate extension-speed limits and may cause another warning or simulated damage.
For the broader operating principles, see our guidance on what an aircraft overspeed alert means and how to respond.
Why does the warning appear at every altitude or below the barber pole?
A warning that follows excessive IAS at low altitude and excessive Mach at high altitude is normal. A warning well below both limits points instead to the selected speed, the aircraft files or a custom panel gauge.
- It stops as soon as speed falls below the pole: the warning is operating normally. Use a lower IAS or Mach target.
- It occurs during every descent: the aircraft is gaining IAS as it descends. Reduce thrust earlier and manage the descent rate.
- It affects only one add-on aircraft: suspect incorrect speed references, mismatched panel and flight-model files, or a custom gauge with its own limit.
- It begins only a few knots below the pole: allow a larger margin. Gauge rounding, turbulence or a moving Mach limit can explain a small discrepancy.
- It affects every aircraft: confirm that the number being watched is IAS rather than TAS or groundspeed, then test an unmodified default aircraft in a new flight.
- It remains active below both IAS and Mach limits: a custom warning gauge or sound may be stuck or incompatible. Restore the matching panel files before changing the flight model.
Should I edit aircraft.cfg to remove the warning?
Edit aircraft.cfg only when an add-on's limits are demonstrably wrong. FS2004 aircraft commonly define them under [Reference Speeds] using max_indicated_speed and max_mach.
Back up the original file, then restore the correct values for that specific aircraft rather than raising them simply to suppress the alert. Our guide to checking and changing FS2004 aircraft speed settings explains the configuration side. These edits will not repair a custom gauge that has an independent overspeed threshold.