Learn what an ILS approach is, how localiser and glideslope guidance work, how to fly one in a simulator, and why capture sometimes fails.
An ILS approach is a precision instrument procedure that uses ground-based radio signals to align an aircraft with a runway. The localiser provides left-right guidance and the glideslope provides vertical guidance. In a flight simulator, tune or confirm the correct ILS, intercept from below, and follow both indications to published minima.
This is a general flight-simulator explanation applicable to Microsoft Flight Simulator, FSX, Prepar3D, X-Plane and similar civilian sims. The radio principles remain the same, but tuning, navigation-source selection and autopilot capture logic vary by aircraft. Our guide to the equipment needed to practise ILS approaches explains the essential receiver and cockpit displays.
What does ILS stand for?
ILS stands for Instrument Landing System, a precision runway guidance system used in reduced visibility or whenever its published instrument procedure is flown. Strictly speaking, the ILS is the radio system; an ILS approach is the procedure specifying how to join its signals, which altitudes to observe, the applicable minima and the missed approach.
Not every airport, runway or runway direction has an ILS. A runway may instead offer a localiser-only, RNAV, RNP or visual approach, and an ILS serving one end does not necessarily serve the opposite end.
ILS procedures are categorised as CAT I, CAT II or CAT III. Progressively lower minima require the complete operation to qualify: suitable ground equipment, serviceable aircraft systems and the necessary operating approval. A simulator aircraft or airport may model only part of that capability.
How does an ILS approach work?
An ILS combines two separate radio guidance signals to define a path towards one specific runway direction: the localiser aligns the aircraft with the extended centreline, while the glideslope defines its descent path.
What is the ILS localiser?
The localiser, spelt localizer in US material, provides lateral guidance. Its aerial is normally beyond the far end of the runway, and the aircraft displays deviation through a CDI, HSI or primary flight display.
On a correctly configured front-course approach, an indication left of centre means the localiser course lies left of the aircraft, so correct towards it. Localiser guidance is angular and becomes increasingly sensitive near the runway. Large late corrections therefore produce oscillation across the centreline; use small heading changes and give each one time to work.
What is the glideslope?
The glideslope, also called the glide path, provides vertical guidance towards the touchdown area. Its published angle is often close to 3°, but the charted angle and altitude restrictions always take priority.
If the glideslope pointer is above centre, the path is above the aircraft. If it is below centre, the aircraft is high relative to the path. The normal technique is to intercept from below at the published altitude rather than dive after the signal from above. Our focused explanation of how simulator glideslope indications and capture work covers this vertical component in more detail.
The localiser and glideslope do not themselves supply distance. Position checks may come from DME, GPS or FMS fixes, depending on the procedure and aircraft. Older approaches may use marker beacons, while many modern procedures rely on DME or defined fixes. Approach and runway lights are not part of the radio guidance, but they become crucial when transitioning to a visual landing.
How do we fly an ILS approach in a flight simulator?
A successful simulator ILS requires correct approach data, a stable localiser intercept and glideslope capture from below. A dedicated ILS simulator is not required; major civilian flight simulators reproduce the signals and indications needed for manual or autopilot-coupled practice.
- Brief the published procedure. Confirm that the selected runway direction has an ILS. Note its identifier, frequency, inbound course, final approach fix, altitude restrictions, decision altitude or height, and missed-approach instructions. Do not assume every glideslope uses exactly 3°.
- Load the approach if appropriate. Selecting the procedure in an FMS or GPS can provide sequencing and fixes, but it does not guarantee that every aircraft will tune the radio or change navigation source automatically.
- Tune and identify the ILS. Enter or confirm the frequency in the correct NAV receiver. Verify the displayed identifier or listen for its Morse identifier if the equipment models it. The paired glideslope frequency is selected automatically; there is normally no separate glideslope frequency to enter.
- Set the course and navigation source. Select the published front course where the panel requires it. Confirm that the instruments and autopilot are using
NAV,VLOCorLOCrather thanGPSorFMS. Some airliners manage this automatically, so follow their mode logic rather than forcing an unnecessary source change. - Establish a stable intercept. Join the localiser at a modest angle, commonly around 20° to 30° unless the procedure or an ATC vector requires otherwise. Be level at the published intercept altitude, below the glideslope, with speed and configuration under control. Arriving high is the setup error we see most often.
- Arm the correct approach mode. Select
APPorAPRwhen appropriate, or fly the indications manually. Check the flight-mode annunciator: it shows whetherLOCandGSare armed or captured. An illuminated approach button may show only that the mode was selected. - Capture and track the guidance. Turn onto the inbound course as the localiser centres. When the glideslope descends towards centre, begin the descent or allow the autopilot to capture it. Localiser capture normally occurs first. Protect the target speed and use small pitch, power and heading corrections.
- Make the decision at minima. Cross-check altitude against DME, named fixes or other published position information rather than staring only at the needles. Continue with the required visual references or a properly configured autoland capability; otherwise execute the published missed approach.
Aircraft-specific controls can differ sharply from this general sequence. Our practical MSFS 2024 setup and capture walkthrough shows how the procedure translates to a modern simulator.
Why will the localiser or glideslope not capture?
Failed ILS capture is usually caused by the wrong frequency, navigation source, intercept geometry or active autopilot mode rather than a defective transmitter.
| Symptom | Likely cause | What to check |
|---|---|---|
| No ILS indication | Wrong frequency, receiver or navigation source; excessive distance; mismatched scenery data | Verify the runway end, identifier, active NAV receiver and radio-navigation source. Compare the aircraft database with the installed airport scenery if they disagree. |
| Localiser appears but no glideslope | Localiser-only procedure, wrong runway direction or an installation without modelled vertical guidance | Confirm that the procedure is published as an ILS rather than LOC-only and that the correct runway end is selected. |
| Glideslope appears but will not capture | The aircraft is above the path, 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. |
APP is selected but nothing captures | Poor intercept angle, excessive speed or the wrong active mode | Check the flight-mode annunciator, reduce the intercept angle and stabilise before the final approach fix. |
| The aircraft turns away or guidance seems reversed | Wrong front course, back-course confusion or incorrect navigation source | Set the published inbound course and intercept the front course from the correct side. Use back-course mode only for a published back-course procedure and compatible equipment. |
| The aircraft oscillates near the runway | Excessive speed, aggressive corrections or weak autopilot tracking as sensitivity increases | Stabilise earlier, make smaller corrections and be prepared to disconnect the autopilot. |
| Glideslope guidance appears well above the expected profile | Possible false upper glideslope lobe | Do not chase it. Re-establish below the path using published altitudes, or abandon the approach and try again. |
Simulator navigation data can create faults even when the cockpit is configured correctly. A replacement airport may use a different frequency from the aircraft's navigation database, while older scenery may retain superseded runway identifiers. Compare both data sources before blaming the autopilot.
Can the autopilot fly and land from an ILS?
Many autopilots can capture and track an ILS, but a coupled approach is not automatically an autoland. Approach mode may control lateral and vertical flight while leaving speed, flaps, landing gear, flare and braking to the pilot.
Monitor the raw deviation indications and flight-mode annunciations throughout. Approach mode cannot rescue an aircraft that is too high, too fast or tracking the wrong signal, and pressing APP does not guarantee that any mode has captured.
Autoland requires a suitably equipped aircraft, an appropriate runway installation, correct configuration and the required autopilot or flight-control channels. If the simulated aircraft does not meet those conditions, disconnect and land manually when visual or fly the missed approach at minima.
Is ILS the same as localiser, autoland or RNAV?
No. ILS is ground-based lateral and vertical guidance, a localiser-only approach has no usable glideslope, autoland is an aircraft capability, and RNAV uses area-navigation guidance rather than the runway's ILS transmitters.
| Approach or capability | Guidance and pilot action |
|---|---|
| ILS | Tune or confirm the ILS, follow localiser and glideslope guidance, and use the published decision altitude or height. |
| Localiser-only | Use the runway-alignment signal, but descend by charted fixes and altitudes to the published minimum descent altitude because no glideslope is available. |
| RNAV or RNP | Keep the appropriate GPS or FMS source selected. Vertical guidance depends on the procedure and aircraft capability. |
| Autoland | Uses compatible aircraft systems to continue beyond normal ILS tracking through flare and, where modelled, rollout. |
| Visual approach | Position and descend mainly by outside references, although an available ILS may still be monitored as a cross-check. |
An LPV approach can display angular lateral and vertical guidance resembling an ILS, but it uses GNSS rather than localiser and glideslope transmitters. Our comparison of ILS radio guidance with RNAV and GNSS approaches explains why their source selection and capture behaviour differ.
Choose the procedure matching the runway, weather, available aircraft equipment and ATC clearance. ILS is often the natural option with a low cloud base and a serviceable runway installation; RNAV is useful where no ILS exists or its published routing better suits the arrival.