What is an ILS approach in aviation and flight simulation?
An ILS approach is a precision instrument approach using ground-based radio signals to guide an aircraft laterally towards a runway centreline and vertically down a descent path. In aviation and flight simulation, the pilot intercepts the localiser and glideslope, follows them to published minima, then lands visually, completes an autoland, or goes around.
In Aviation & Real-World Flying, ILS means Instrument Landing System. Strictly speaking, the ILS is the navigation system; an ILS approach is the published procedure that tells the pilot how to join its signals, what altitudes to observe and what to do after reaching the decision altitude or height.
How does an ILS approach work?
An ILS combines a horizontal localiser signal with a vertical glideslope signal to define a path towards one specific runway direction.
| Element | What it provides | What the pilot sees |
|---|---|---|
| Localiser | Lateral guidance towards the extended runway centreline | A horizontal deviation indication, usually labelled LOC |
| Glideslope | Vertical guidance down a published descent angle, commonly close to 3° | A vertical deviation indication, usually labelled GS |
| Associated fixes or DME | Distance or position checks where provided | DME distance, waypoint information or charted fixes |
A centred localiser indication means the aircraft is on the lateral course; a centred glideslope indication means it is on the vertical path. The beams become increasingly sensitive near the runway, so the large corrections that work during interception can cause oscillation close to the threshold.
The published chart supplies the ILS frequency, inbound course, intercept altitudes, minima and missed-approach instructions. Marker beacons may appear on older procedures, but many installations use DME or defined fixes instead. Approach and runway lights are not radio-guidance components, although they are crucial when transitioning from instruments to a visual landing.
How do you fly an ILS approach in a simulator?
To fly an ILS in a simulator, select the correct runway procedure, tune and identify its frequency, choose the localiser navigation source, intercept from below and monitor both the guidance and the aircraft's mode annunciations.
- Load or review the published approach. Confirm the runway direction, localiser frequency, front course, intercept altitude, decision altitude or height, and missed-approach procedure. Selecting an approach in a flight plan does not guarantee that every simulated aircraft will tune it automatically.
- Tune and identify the ILS. Place the frequency in the appropriate navigation receiver and listen for or verify the identifier where the aircraft models it. Modern airliners may tune the frequency through the flight-management system.
- Select the correct navigation source. A glass-cockpit aircraft may require
VLOC,LOCor a similar radio-navigation source rather than GPS. The setup error we see most often is an aircraft following the magenta GPS course while the pilot expects it to capture the localiser. - Approach the localiser at a sensible angle. Follow the published transition or ATC vector, usually using a shallow intercept rather than crossing the beam at a right angle. Set the published front course and avoid approaching from the back-course side unless a separate back-course procedure is published.
- Remain below the glideslope before capture. Level at the charted intercept altitude and let the glideslope descend towards the aircraft. Intercepting from above can prevent capture and risks following a false upper lobe.
- Arm approach mode and verify capture. Pressing
APPorAPRonly arms the system. Check that the flight-mode annunciations change from armed to captured, normally localiser first and glideslope second. Configure the aircraft, reduce speed and monitor the descent rather than assuming the autopilot will correct every setup error. - Make the decision at minima. Continue only with the required visual reference and a stable aircraft. Otherwise, execute the published missed approach. A simulator may let the aircraft descend regardless, but that is not a correctly completed instrument approach.
Aircraft controls and automation differ significantly. Our MSFS 2024 setup and capture walkthrough covers modern Microsoft Flight Simulator procedures, while the FSX frequency, course and interception procedure explains the older simulator's workflow.
Why will the localiser or glideslope not capture?
An ILS usually fails to capture because the wrong frequency or navigation source is selected, the aircraft has poor intercept geometry, or it is already above the glideslope.
| Symptom | Likely cause | Practical fix |
|---|---|---|
| No localiser indication | Wrong frequency, receiver or navigation source; excessive distance; incompatible scenery or navigation data | Verify the runway identifier and frequency, activate the correct receiver, select radio navigation and check for scenery or database mismatches |
| Localiser appears but no glideslope | The procedure is localiser-only, the wrong runway end is selected, or the simulated installation lacks vertical guidance | Confirm that the procedure is published as an ILS rather than LOC and that the chosen runway direction matches |
| Glideslope is visible but will not capture | The aircraft is above the beam, approach mode is not armed, or required localiser capture has not occurred | Reposition below the glideslope at the charted altitude and verify the armed and captured mode annunciations |
| Aircraft turns away from the runway | Wrong front course, back-course interception or incorrect navigation source | Set the published inbound course and intercept the front course from the correct side |
| Aircraft oscillates near the runway | Excessive speed, aggressive corrections or weak autopilot behaviour as beam sensitivity increases | Stabilise earlier, use smaller corrections and be prepared to disconnect the autopilot |
FSX has several aircraft- and scenery-specific variations; our FSX glideslope capture fault guide works through those failure modes in more detail.
Is an ILS approach the same as autoland or RNAV?
No: ILS is a ground-based guidance system, autoland is an aircraft capability, and RNAV is a different method of navigating an instrument approach.
Autoland requires a suitably equipped aircraft, an appropriate runway installation, the required serviceability and a correctly performed procedure. Many general-aviation autopilots can follow an ILS but cannot flare or control the rollout. Even in an airliner simulation, pressing APP does not by itself guarantee autoland; the necessary autopilot channels and landing modes must engage and remain operational.
ILS categories permit progressively lower operating minima, but the available category depends on the complete operation: airport equipment, aircraft certification, system status and crew authorisation. A simulator add-on may model only part of that chain.
RNAV approaches use GPS or flight-management guidance rather than a runway's localiser transmitter. An LPV approach can display angular lateral and vertical guidance that resembles an ILS, but it uses different navigation sources and autopilot modes. Our GPS and RNAV approach setup guide explains those operational differences.
Choose the published approach that matches the runway, weather, available equipment and ATC clearance. ILS is often the natural choice in a low cloud base when the runway has a serviceable installation; RNAV is useful where no ILS exists or where its routing better suits the arrival.