What is an ILS approach and how does it work in a simulator?

ILS stands for Instrument Landing System. An ILS approach is a precision instrument procedure that uses a runway’s ground-based localiser for left-right guidance and glideslope for vertical guidance. In a flight simulator, you tune or confirm the ILS, select the radio navigation source, intercept from below, and follow it to published minima.

The simulator scope here is General. The same radio principles apply in Microsoft Flight Simulator, FSX, Prepar3D, X-Plane and comparable civilian simulators, although tuning, source selection, autopilot modes and system depth vary between aircraft.

What does ILS stand for in aviation?

ILS means Instrument Landing System, the ground-based radio system that guides an aircraft towards one specific runway direction.

The ILS system and the ILS approach are related but not identical. The system supplies guidance signals; the published approach procedure specifies the route, intercept altitude, inbound course, fixes, decision altitude or height and missed-approach instructions used with those signals.

Not every airport or runway has an ILS, and an installation serving one end of a runway does not necessarily serve the opposite end. Other runway approaches may use a localiser without a glideslope, RNAV or RNP guidance, or visual references.

What do CAT I, CAT II and CAT III mean?

ILS categories describe operations with progressively lower decision heights and visibility requirements, but the category printed for a runway is only one part of the operation.

The ground installation, aircraft equipment, crew qualification and operating approval must all support the category being flown. In a simulator, a CAT II or CAT III label does not prove that the aircraft model has fully implemented autoland, redundancy or rollout guidance. Exact minima come from the applicable approach chart rather than the category name alone.

How does an ILS approach work?

An ILS approach combines two independent steering signals: the localiser aligns the aircraft laterally with the extended runway centreline, while the glideslope defines the vertical descent path.

What is the ILS localiser?

The localiser, written as localizer in US material, provides left-right guidance. Its aerial is normally positioned beyond the far end of the runway, transmitting a course along the runway centreline and its extension.

With the published front course set and normal sensing, a deviation bar or diamond left of centre means the course is to the aircraft’s left. Correct towards it. Localiser guidance is angular, so the same needle movement represents a smaller lateral distance as the aircraft approaches the runway; large late corrections often cause an oscillation across the centreline.

The course selector does not rotate or reposition the transmitted beam. It configures the cockpit display and, in some aircraft, affects autopilot capture logic. Reverse sensing and misleading indications can result from an incorrect course or an improperly flown back-course approach.

What is the ILS glideslope?

The glideslope, also called the glide path, supplies vertical guidance towards the runway’s touchdown area. Many use an angle close to 3°, but the charted angle and altitude restrictions 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 method is to remain level at the published intercept altitude and capture the glideslope from below as the pointer moves towards the centre.

Trying to capture from above may produce an unstable descent or no autopilot capture at all. ILS transmitters can also produce false upper lobes, which is another reason never to chase an unexpected glideslope above the published profile.

The localiser and glideslope steering signals do not themselves provide distance. The procedure may use DME, GPS or FMS fixes, and some older installations use marker beacons. For a closer look at the display logic, see our explanation of how localiser and glideslope indications differ.

How is ILS simulated in a flight simulator?

An ILS simulation uses the virtual airport’s navigation data and transmitter positions to calculate localiser and glideslope deviation for the aircraft’s radio receiver and cockpit instruments.

Loading an ILS procedure into an FMS or GPS draws the arrival and supplies useful fixes, but it is not the same as receiving the ILS. Depending on the aircraft, the ILS frequency may need to be tuned manually, automatically selected by the FMS, or confirmed on a radio-navigation page. The active display and autopilot must then use the appropriate radio source.

A separate, dedicated ILS simulator is not required. Major civilian flight simulators can reproduce manual and autopilot-coupled approaches, though not every product models terrain shielding, radio interference, transmitter failures, certification logic or low-visibility operations in full.

Airport scenery and aircraft navigation data can also disagree. A replaced airport may use a different runway designation or frequency from an older aircraft database, leaving the cockpit procedure and simulated transmitter out of step.

How do you fly an ILS approach in a simulator?

A reliable simulator ILS procedure starts with the correct runway data, joins the localiser at a manageable angle and captures the glideslope from below.

1. Brief the approach. Confirm the runway direction, ILS identifier and frequency, inbound course, final approach fix, intercept altitude, decision altitude or height and missed-approach procedure. Use data that matches the airport and simulator navigation cycle where possible.
2. Load the procedure if needed. Selecting the approach in the FMS or GPS can provide routing and fix sequencing. Check for discontinuities, but do not assume that loading it has tuned the ILS or selected the correct radio source.
3. Tune and identify the ILS. Enter or confirm the localiser frequency in the correct NAV receiver, make it active and verify the displayed or audible identifier where the aircraft models one. The associated glideslope frequency is paired automatically; pilots do not normally tune it separately.
4. Set the course and source. Set the published front course where the panel requires it. Select NAV, VLOC or the aircraft’s equivalent radio-navigation source rather than leaving the display in GPS or FMS. Some airliners switch automatically, so confirm the annunciation instead of changing it blindly. Our source-selection guide explains why a conventional ILS needs NAV or VLOC rather than GPS guidance.
5. Establish the intercept. Approach the localiser with a modest intercept angle, often about 20° to 30° unless the procedure or simulated ATC gives something different. Be level at the published altitude, below the glideslope, with speed and configuration under control. Arriving high is one of the setup errors we see most often.
6. Arm approach mode. Select APP or APR at the appropriate point, or hand-fly the raw indications. Watch the flight-mode annunciator for armed and captured LOC and GS modes; an illuminated approach button alone does not confirm capture.
7. Capture and track. Allow the aircraft to turn onto the inbound course as the localiser centres. Localiser capture normally occurs before glideslope capture. When the glideslope reaches the centre from above, begin the descent or verify that the autopilot has captured it. Use small corrections and keep monitoring speed, power, configuration and both deviation indicators.
8. Act at minima. Cross-check altitude and position rather than staring only at the needles. At the published decision altitude or height, continue only with the required visual references and a suitable landing position, or with a correctly configured autoland operation. Otherwise execute the published missed approach.

Aircraft controls and mode sequences differ, but the underlying flow remains the same. Our simulator-agnostic cockpit procedure for flying an ILS provides a shorter practical checklist.

Why will the localiser or glideslope not capture?

Failed ILS capture is usually caused by the wrong frequency, receiver, navigation source, intercept position or autopilot mode rather than a defective ILS.

If lateral guidance is normal but the vertical pointer never appears, use these targeted checks for a missing glideslope. Also compare the aircraft’s procedure data with the installed airport scenery when frequencies, runway numbers or final approach tracks disagree.

Can the autopilot fly and land from an ILS?

Many autopilots can capture and track an ILS, but an autopilot-coupled approach is not automatically an autoland.

During an ordinary coupled approach, the autopilot may control localiser and glideslope tracking while the pilot manages speed, flaps, landing gear, decision-making and the eventual manual landing. Some systems also require the pilot to manage thrust throughout.

Autoland requires a suitably modelled aircraft, compatible runway facilities, the correct configuration and the required autopilot or flight-control channels. Depending on the aircraft, it may provide flare, touchdown and rollout guidance. Pressing APP does not create those capabilities.

Always monitor the raw localiser and glideslope indications and the flight-mode annunciator. If the aircraft captures the wrong mode, diverges from the beam or becomes unstable, disconnect the automation and correct manually or fly the missed approach.

Is ILS the same as localiser, RNAV or autoland?

No. These terms describe different guidance systems, procedures or aircraft capabilities, even when their cockpit indications look similar.

Choose the procedure published for the runway, supported by the aircraft and appropriate to the simulated clearance and conditions. Do not substitute an ILS for an assigned RNAV procedure merely because both lead to the same runway.