Understand ILS glideslope guidance in flight simulators: GS pointer meanings, coverage, ‘glideslope alive’, MSFS capture steps and common fixes.
An ILS glideslope is the vertical part of an Instrument Landing System, usually defining a descent of about 3 degrees towards the runway touchdown zone. In a flight simulator, the simulated navigation receiver derives the aircraft’s position relative to that modelled beam and drives a GS pointer, flight director or autopilot command.
This is General simulator guidance. The underlying principles apply across MSFS, FSX, Prepar3D, X-Plane and other simulators, but receiver controls, indications and autopilot capture logic depend on the aircraft and avionics being simulated.
How does an ILS glideslope work in aircraft?
An ILS ground installation transmits separate lateral and vertical guidance: the localiser leads the aircraft towards the runway centreline, while the glideslope, usually labelled GS or G/S, defines the descent angle.
The real glideslope signal uses overlapping 90 Hz and 150 Hz modulation patterns. The airborne receiver compares their relative strength; equal modulation places the aircraft on the intended path, while an imbalance indicates that it is above or below it. Simulators usually reproduce the resulting deviation from the aircraft’s position relative to a modelled transmitter rather than physically simulating every reflection, obstruction and multipath effect.
The glideslope transmitter uses a paired UHF channel, but the pilot normally tunes only the published VHF localiser frequency. The receiver selects the paired glideslope channel automatically. Modern airliners may tune it through the flight-management system, while conventional panels use a NAV receiver.
The course selector does not rotate or move the transmitted beam. Setting the published inbound course gives a meaningful display and may be required by the simulated avionics, but it cannot correct a wrongly tuned facility.
| Guidance | Purpose | Typical indication |
|---|---|---|
| Localiser | Left-and-right guidance to the runway centreline | LOC |
| ILS glideslope | Radio-based vertical guidance for an ILS | GS or G/S |
| RNAV glidepath | Computed vertical guidance for a suitable RNAV approach | GP |
A glidepath marked GP is not an ILS glideslope. Our comparison of ILS and RNAV vertical guidance explains when to use each. To display an ILS, the simulated aircraft needs an ILS-capable receiver and a CDI, HSI or primary flight display; an autopilot is optional. See our guide to the cockpit equipment used for simulated ILS approaches for the common panel arrangements.
What does the glideslope pointer show?
A conventional glideslope pointer shows where the desired path lies relative to the aircraft: fly gently towards the pointer rather than moving away from it.
| GS pointer position | Aircraft position | Appropriate response |
|---|---|---|
| Above centre | Below the glideslope | When intercepting level, hold altitude until the pointer approaches the centre. If already descending, reduce the descent rate gently. |
| Centred | On the glideslope | Maintain a stable speed, configuration and descent rate. |
| Below centre | Above the glideslope | Do not dive after it. Re-establish a safe, stable approach or go around. |
This fly-towards-the-pointer rule applies to a deviation diamond or needle. Flight-director bars are command indications: they tell the pilot which control input to make, so they should not be confused with the GS deviation pointer beside the attitude display.
The indication also becomes increasingly sensitive near the runway. A small displacement close to the threshold represents much less physical distance than the same displacement several miles out, which is why large late pitch corrections produce oscillation.
What does “glideslope alive” mean?
Glideslope alive means the GS pointer has moved into view—normally from the top of the scale during a level intercept from below—and is travelling towards the centre.
It confirms that the receiver is detecting usable vertical guidance, but it does not mean the autopilot has captured it. Remain at the published intercept altitude until the pointer centres and the flight-mode annunciator changes from GS armed to GS captured. Beginning the descent merely because someone calls “glideslope alive” places the aircraft below the proper path.
How much glideslope coverage is available?
Standard ILS glideslope coverage is normally usable to at least 10 nautical miles within approximately 8 degrees either side of the localiser centreline, although individual facilities can have approved extended coverage.
That is narrower and shorter than typical localiser coverage. Reception outside the nominal area, or an indication obtained from the wrong side of the runway, must not be treated as valid approach guidance. The published intercept fix, altitude and final approach segment remain the proper basis for joining the beam.
False glideslope lobes can exist above the normal path, which is another reason to intercept from below. Some simulators model false or restricted signals; others provide an idealised beam that can be received too far away or from unrealistic positions. Airport scenery can also move the visible runway without moving the navigation facility, leaving the pointer centred while the runway appears offset.
How do you capture an ILS glideslope?
The reliable method is to intercept the localiser at the published altitude, approach the glideslope from below and arm approach mode before the pointer centres.
- Check the procedure. Confirm that it is an ILS rather than a localiser-only approach, then note the runway, frequency, inbound course, intercept altitude and minimums. A procedure labelled LOC may provide no glideslope.
- Tune and identify the ILS. Put the localiser frequency in the active NAV receiver or select it through the aircraft’s radio-navigation system. Check the identifier when the simulation models it.
- Display the correct source. On CDI-equipped general-aviation panels, select NAV, LOC or VLOC rather than GPS. Integrated airliner avionics may manage the source internally, but the ILS scales and identification should still be visible.
- Join from below. Intercept the localiser at a shallow angle—about 30 degrees or less is a practical target—and remain level at the charted altitude. The GS pointer should descend from above towards the centre.
- Arm approach mode. Select
APR,APPRor the equivalent and inspect the flight-mode annunciator. Localiser and GS should appear as armed modes; selecting NAV or LOC alone often provides lateral capture without vertical capture. - Confirm capture before descending. At capture, the GS mode changes from armed to active and the autopilot or flight director commands a descent. Do not rely on the button light alone.
- Monitor the approach. Hold the target speed and configuration, make small corrections and cross-check altitude against distance. If guidance becomes unreliable or the approach is unstable, go around rather than chasing a full-scale pointer.
For the complete sequence from tuning through minimums, use our step-by-step simulator ILS approach procedure.
What descent rate should a 3-degree glideslope produce?
A 3-degree glideslope requires a vertical speed of roughly groundspeed multiplied by 5.3; multiplying by 5 gives a quick cockpit estimate.
- 120 knots groundspeed: about 600–640 feet per minute
- 140 knots groundspeed: about 700–740 feet per minute
- 160 knots groundspeed: about 800–850 feet per minute
Use groundspeed, not indicated airspeed. Wind changes the required vertical speed even though it does not move the ILS beam. The pointer remains the primary guidance; the calculation is a useful cross-check for an implausible capture or unstable descent.
How does the glideslope work in MSFS?
In Microsoft Flight Simulator 2020 and Microsoft Flight Simulator 2024, an ILS glideslope follows the same principles, but tuning, source selection and capture logic are implemented by the individual aircraft’s avionics.
- Garmin-style panels: Confirm that the CDI source shows VLOC or LOC rather than GPS. Some units can switch automatically when an approach is loaded, but implementation varies between aircraft.
- Airliner panels: Displaying the ILS scales is not always the same as arming approach mode. On many Airbus-style panels, for example, the LS control displays guidance while APPR arms localiser and glideslope capture.
- Default and add-on aircraft: Autopilot mode logic can differ even when the PFD looks similar. Trust the flight-mode annunciator rather than assuming a labelled button has produced capture.
- Replacement airport scenery: The scenery’s runway position or ILS data can disagree with the aircraft navigation database. Verify the frequency and identifier if the beam points away from the visible runway.
FSX and many older panels use the same underlying technique but are more likely to require manual NAV1 tuning and an explicit GPS/NAV source switch.
Why will the glideslope not appear or capture?
A missing or uncaptured glideslope is usually caused by the wrong approach, frequency, navigation source, intercept geometry or autopilot mode.
| Symptom | Likely cause | Fix |
|---|---|---|
| No GS pointer or GS flag remains visible | Wrong frequency, standby frequency selected, localiser-only approach or aircraft outside coverage | Verify the active frequency, runway and procedure, then establish on the published final approach. |
| Localiser works but no vertical guidance appears | The procedure has no GS, the wrong runway end is selected or navigation/scenery data disagree | Check that the procedure is specifically an ILS and confirm its identifier and runway direction. |
| Pointer moves but autopilot stays level | APPR is not armed, only LOC/NAV is active or capture conditions have not been met | Arm approach mode and inspect the annunciator for GS armed, then GS captured. |
| GS remains armed as the aircraft passes through it | The aircraft is above the beam, not established on the localiser or using the wrong navigation source | Do not dive to recover it. Reposition for an intercept from below or go around. |
| GS captures unusually high or commands a steep descent | Possible false lobe or unrealistic intercept geometry | Discontinue the approach and rejoin at the published altitude from below. |
| Needle is centred but runway is displaced | Wrong ILS or mismatch between airport scenery and navigation data | Verify the facility and use matching scenery/navigation data before attempting the approach again. |
| Aircraft oscillates around the beam | Excessive speed, late configuration, large manual corrections or poor autopilot implementation | Stabilise speed and power, make smaller corrections and disconnect a malfunctioning autopilot if necessary. |
A back-course localiser should not be flown using its reciprocal glideslope. Unless a published procedure explicitly supplies approved vertical guidance, treat a back-course approach as lateral guidance only.
Does following the glideslope land the aircraft automatically?
No. Glideslope capture supplies vertical approach guidance; it does not by itself flare, reduce thrust, touch down or control the landing rollout.
Those functions require a compatible aircraft, runway installation and correctly configured autoland system. Many simulated autopilots can track LOC and GS accurately but still require manual landing at the applicable decision altitude. The glideslope itself points towards the touchdown area and does not perform the flare.
Our explanation of autoland requirements and mode sequencing in a flight simulator covers what must happen after ordinary localiser and glideslope tracking.