How does an ILS glideslope work in a flight simulator?

An ILS glideslope is the vertical guidance component of an Instrument Landing System, normally leading an aircraft down a roughly 3-degree descent towards the runway touchdown zone. In a flight simulator, the aircraft's navigation receiver displays deviation from that radio beam, while the pilot or autopilot corrects the descent to keep it centred.

Is the glideslope the same as the localiser?

No. The localiser provides left-and-right guidance towards the runway centreline, while the glideslope, usually shown as GS, provides up-and-down guidance. Our explanation of how both ILS components fit together covers the complete approach concept.

The ground installation transmits overlapping signals above and below the intended descent path. The aircraft's receiver compares them and moves a needle, diamond or pointer to show whether the aeroplane is above or below the beam. A simulator reproduces this from the virtual aircraft's position relative to the modelled ILS transmitter; the depth of radio propagation and interference modelling varies between simulators and aircraft add-ons.

Tuning the published localiser frequency also selects its paired glideslope channel internally, so there is normally no separate GS frequency to enter. Some modern aircraft tune the ILS through the flight management system, while older panels require manual tuning in a NAV radio. The selected navigation source must normally be NAV, LOC or VLOC rather than GPS.

This is a fly-towards-the-pointer convention used by common CDI, HSI and glass-cockpit displays. Always confirm the presentation used by the simulated aircraft rather than making a large pitch correction from an unfamiliar indication.

How do you capture an ILS glideslope?

The reliable method is to intercept the localiser at the published altitude while positioned below the glideslope. The mistake we see most often is descending onto the approach from above and expecting the autopilot to capture the beam.

1. Confirm the approach data. Check the simulated airport's ILS frequency, inbound course and charted intercept altitude. Airport scenery and navigation data can occasionally disagree.
2. Tune and identify the ILS. Place the frequency in the active NAV receiver or select it through the aircraft's flight-management system. Set the published front course where the panel requires it.
3. Select the correct navigation source. Change from GPS or FMS guidance to LOC, NAV or VLOC as required by that aircraft. A GPS route can lead to the final approach but cannot display an ILS glideslope while the receiver remains in GPS mode.
4. Join from below. Intercept the localiser at a shallow angle, preferably about 30 degrees or less, and remain level at the published altitude. The GS pointer should move towards the centre as the beam reaches the aircraft.
5. Arm approach mode. When using the flight director or autopilot, select APPR or APR and check the mode annunciations. Look for localiser capture and GS armed, followed by GS capture; merely selecting NAV or LOC may provide lateral guidance without vertical capture.
6. Follow the descent. Once centred, make small pitch and power changes, maintain the target speed and avoid chasing every needle movement. The indication becomes more sensitive as the runway gets closer.

Controls and annunciations differ between panels. A worked MSFS 2024 glideslope capture sequence shows how this process applies in that simulator.

Why will the glideslope not capture?

A glideslope usually fails to capture because the aircraft is above the beam, using the wrong navigation source or has not armed approach mode.

• Intercepting from above: Return to the published procedure rather than diving after the pointer. Real ILS installations can produce false lobes above the normal path, although simulator modelling of them varies.
• GPS is still selected: Change the CDI or navigation source to the tuned ILS receiver. An RNAV glidepath marked GP is different from an ILS glideslope marked GS.
• The frequency is wrong or still in standby: Verify the active frequency, runway direction and localiser identification.
• Only LOC or NAV mode is active: Arm APPR or APR and confirm GS appears as an armed mode on the flight-mode annunciator.
• The wrong runway end is being approached: A back-course approach normally has no usable glideslope. Do not follow a GS indication from the reciprocal side unless the published procedure and aircraft explicitly support it.
• The aircraft is outside coverage: Glideslope reception is more restricted than localiser reception. Establish on the published final approach rather than expecting capture far from the runway.
• Scenery and navigation data disagree: A replacement airport may place or tune the ILS differently from the aircraft database. Compare the simulator's data with the approach information being used.

For the older simulator, our FSX glideslope troubleshooting steps cover its common receiver and autopilot problems in more detail.

Does the glideslope land the aircraft automatically?

No. Glideslope capture means only that the aircraft or autopilot can follow vertical ILS guidance; it does not guarantee an automatic landing.

Autoland requires a suitably equipped aircraft, compatible autopilot modes, an appropriate runway installation and correct crew configuration. Many simulated autopilots can track LOC and GS but cannot flare, reduce thrust or control the landing rollout. At the applicable decision altitude or minimums, the pilot must obtain the required visual reference and continue manually, use a correctly configured autoland system, or go around.

The beam guides the aircraft towards the touchdown area, not through the flare. Wind does not move the ILS beam, but it changes the crab angle, power and control inputs needed to remain centred.