What is an ILS approach and how does it work in a simulator?
An ILS approach is an Instrument Landing System procedure that uses radio guidance to align an aircraft with a runway. The localiser provides left-right guidance, while the glideslope provides vertical guidance. In a flight simulator, tune or confirm the correct ILS, intercept from below, then follow both indications to the 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 are the same; cockpit controls, automatic tuning and autopilot capture logic vary by aircraft.
What does ILS stand for?
ILS stands for Instrument Landing System, a precision runway approach system used to guide an aircraft laterally and vertically in reduced visibility or whenever an instrument approach is required.
Not every airport, runway or runway direction has an ILS. A runway may instead have a localiser-only, RNAV, RNP or visual procedure. An ILS also does not automatically mean autoland: most ILS approaches end at a decision altitude or decision height, where the pilot must see the required visual references or fly the missed approach.
ILS procedures may be categorised as CAT I, CAT II or CAT III. The lower minima associated with CAT II and CAT III operations require suitable ground equipment, aircraft systems and operating approval; a simulator aircraft may model only part of that capability.
How does an ILS approach work?
An ILS approach combines two separate radio guidance signals: the localiser aligns the aircraft with the runway centreline, and the glideslope provides the descent path.
What is the ILS localiser?
The localiser, spelt localizer in US material, provides lateral guidance along the extended runway centreline. Its aerial is normally beyond the far end of the runway, and the cockpit displays the signal through a course deviation indicator, HSI or primary flight display.
On a correctly configured front-course approach, a deviation bar to the left means the localiser course lies left of the aircraft, so correct towards it. The signal is angular and becomes increasingly sensitive near the runway. Large late corrections therefore produce the familiar weaving approach; use small heading changes and let each correction take effect.
What is the glideslope?
The glideslope, also called the glide path, supplies vertical guidance towards the runway touchdown area. The published angle is often close to 3°, but the charted value 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 the glideslope from below at the published altitude rather than dive after it from above.
The localiser and glideslope alone do not give distance. Distance checks may come from DME, GPS or FMS fixes, depending on the procedure and aircraft. Older approaches may also use marker beacons, although many simulator panels and modern procedures rely on other position checks.
How do we fly an ILS approach in a flight simulator?
A good simulator ILS starts with correct approach data, a stable intercept and glideslope capture from below. A dedicated ILS simulator is not required; the major civilian flight simulators reproduce the signals and indications needed for manual or autopilot-coupled practice.
Before setting up, obtain the runway frequency, inbound course, intercept altitude, minima and missed-approach instructions. Our guide to finding ILS frequencies, courses and chart data in a simulator explains where to check them and why scenery or navigation-database mismatches matter.
- Brief the published procedure. Confirm the runway really has an ILS, then note its identifier, frequency, front course, final approach fix, altitude restrictions, decision altitude or height, and missed approach. Do not assume every runway uses a 3° path.
- Load the approach if appropriate. Selecting the ILS procedure in an FMS or GPS can provide sequencing and fixes, but it does not guarantee that every aircraft will tune the receiver or change the navigation source automatically.
- Tune and identify the ILS. Enter or confirm the frequency in the correct NAV receiver. Check the displayed identifier or listen to the Morse identifier if the simulated equipment supports it. The paired glideslope frequency is selected by the receiver; 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
NAVorLOCrather thanGPSorFMS. Some airliners manage this automatically, so follow the aircraft's mode logic rather than forcing an unnecessary source change. - Intercept in a stable position. Approach the localiser at a modest angle, commonly around 20° to 30° unless the procedure dictates 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. Use
APPorAPRwhen appropriate, or fly the needles manually. Watch the flight-mode annunciations: they show whetherLOCandGSare armed or captured, while an illuminated button may show only that a mode was selected. - Capture the localiser, then the glideslope. Turn onto the inbound course as the lateral deviation centres. When the glideslope moves down towards centre, begin the descent or allow the autopilot to capture it. Make small pitch, power and heading corrections while protecting the target speed.
- Continue only to the authorised minima. Cross-check altitude against distance or named fixes rather than staring only at the needles. At decision altitude or decision height, continue if the required runway references are visible; otherwise execute the published missed approach.
For cockpit-specific controls, follow our practical MSFS 2024 ILS procedure or the separate FSX walkthrough for traditional radios and autopilots.
Why will the localiser or glideslope not capture?
Failed ILS capture is usually caused by the wrong frequency, navigation source, intercept geometry or autopilot mode rather than a defective transmitter.
| Symptom | Likely cause | What to check |
|---|---|---|
| No ILS indication | Wrong frequency, receiver or navigation source | Verify the runway-end frequency, active NAV radio, identifier and NAV/LOC source. Compare the simulator's data with the airport scenery if they disagree. |
| Localiser appears but no glideslope | Localiser-only procedure, aircraft above the path, or glideslope mode not armed | Confirm that the procedure is an ILS rather than LOC-only, then intercept at the published altitude from below. |
APP selected but nothing captures | Poor intercept angle, excessive speed or incorrect active mode | Check the flight-mode annunciator, reduce the intercept angle and establish the aircraft before the final approach fix. |
| Aircraft repeatedly overshoots the localiser | Late capture, excessive speed or corrections that are too large | Slow earlier, use a shallower intercept and make small heading changes as localiser sensitivity increases. |
| Needle guidance appears reversed | Wrong front course or back-course confusion | Set and verify the published inbound course. Use back-course mode only for a published back-course procedure and compatible equipment. |
| Glideslope indication appears while well above profile | Possible false glideslope lobe | Do not chase it. Re-establish below the path using the published altitudes, or abandon the approach and try again. |
Another common simulator-specific cause is mismatched data. A replacement airport may model a frequency different from the one stored in the aircraft's navigation database, while an older simulator may use older runway identifiers. If the setup is correct but no signal appears, 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 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 pointed at the wrong signal.
Autoland requires an aircraft and simulated avionics that support it, the correct configuration, a suitable ILS procedure and the required autopilot or flight-control channels. If those conditions are not met, disconnect and land manually when visual, or fly the missed approach at minima.
What is the difference between ILS, localiser and RNAV?
An ILS gives both lateral and vertical radio guidance, a localiser-only approach gives lateral radio guidance, and RNAV or RNP uses area-navigation guidance from the aircraft's GPS and FMS.
- ILS: tune or confirm the ILS frequency, follow the localiser and glideslope, and use the published decision altitude or height.
- Localiser-only: use the same precise runway-alignment signal but descend according to charted altitudes, fixes and the published minimum descent altitude because there is no usable glideslope.
- RNAV or RNP: keep the appropriate GPS or FMS source selected. Vertical guidance depends on the procedure and aircraft capability; our simulator guide to flying an RNP approach covers that workflow.
- Visual approach: position and descend mainly by outside visual references, although an available ILS can still be monitored as a cross-check.
Loading an RNAV approach with a vertical path does not turn it into an ILS, and loading an ILS in the flight plan does not always tune the radio. Check the procedure type, active navigation source and mode annunciations before every final approach.