Why doesn't every runway have an ILS? Cost, terrain, traffic, interference and RNAV alternatives determine which runway ends receive one.
Not every runway has an ILS because the system is expensive to install, certify and maintain, and many runway ends do not generate enough low-visibility traffic to justify it. Terrain, buildings, radio interference, protected-area requirements and obstacle-clearance limits can also make installation impractical; RNAV or visual approaches often provide a better fit.
In real-world aviation, an ILS belongs to a specific runway approach direction, not simply to the strip of pavement. A runway numbered 09/27 might therefore have an ILS for Runway 09 but no ILS for Runway 27.
What determines whether a runway gets an ILS?
An airport equips a runway end when the operational benefit justifies the installation and a compliant approach can be designed around the site.
| Decision factor | Why it matters |
|---|---|
| Traffic and weather | Busy airports with frequent fog, low cloud or commercial operations gain more from lower approach minima than lightly used airfields in generally good weather. |
| Installation and upkeep | The airport needs localizer and glideslope transmitters, power, monitoring, shelters, inspections, maintenance and eventual equipment replacement. |
| Available land | The localizer array is normally beyond the far end of the runway, while the glideslope equipment sits beside the touchdown area. Roads, boundaries or unsuitable ground can prevent proper siting. |
| Signal quality | Terrain, hangars, fences, aircraft and moving vehicles can reflect or disturb the signals. Protected critical and sensitive areas may also restrict taxiing during low-visibility operations. |
| Obstacles and procedure design | A safe final approach, threshold crossing and missed approach must all be possible. Installing transmitters does not remove hills, towers or protected-airspace conflicts. |
| Supporting infrastructure | Lighting, markings, backup power and low-visibility procedures affect the minima the airport can support. CAT II and CAT III operations require much more than a basic ILS installation. |
Frequency assignments must also be co-ordinated so that nearby systems do not provide misleading guidance. Our explanation of how ILS localizer and glideslope frequencies are allocated covers the separate radio bands involved.
There is no universal traffic figure at which an ILS becomes mandatory. Airport operators, procedure designers and aviation authorities consider demand, weather, terrain, airspace and the cost of maintaining the system for its full service life.
Does one ILS serve both ends of a runway?
No: an ILS is normally installed and certified for one approach direction, so the reciprocal runway end needs separate equipment if it is to have a full ILS.
A localizer signal may have a usable back course, but pilots may fly it only when an authorised back-course procedure is published. It normally provides lateral guidance without a glideslope and is not the same as having a full ILS in the opposite direction.
Airports usually prioritise the runway direction used most often in instrument weather, particularly when it offers the best wind, runway length and obstacle environment. A secondary or crosswind runway may receive only a non-precision approach, an RNAV procedure or no instrument approach at all.
What do pilots use when a runway has no ILS?
Pilots use whichever published procedure their aircraft, crew and operator are authorised to fly, or they land visually when conditions permit.
- RNAV or RNP: Satellite-based procedures can provide lateral guidance and, in forms such as LPV or LNAV/VNAV, approved vertical guidance without installing ILS transmitters at every runway end. Our comparison of ILS and RNAV guidance explains the operational differences.
- Localizer-only approach: This supplies centreline guidance but no ILS glideslope, so altitude is managed using the published descent profile.
- Other conventional approaches: Some airports retain VOR or NDB procedures, although their availability depends on the local navigation infrastructure.
- Visual approach: When visibility and cloud clearance are sufficient, pilots can approach using visual references rather than instrument landing guidance.
A runway without an ILS is not inherently unsafe. It may simply have higher landing minima, require different aircraft equipment, or become unavailable when the weather falls below the applicable limits. An ILS-equipped runway does not automatically permit autoland either; the ILS category, airport facilities, aircraft, crew and operator approvals must all support it.
Why does a flight simulator runway show no ILS?
A simulator runway usually shows no ILS because the real runway end lacks one, the selected procedure is RNAV or localizer-only, or the simulator's navigation data and airport scenery do not agree.
- Check the runway end: Runway 09 and Runway 27 are separate approach directions. Selecting the reciprocal end is a mistake we see constantly.
- Read the procedure type: Confirm that it says ILS rather than LOC, RNAV, RNP or visual. Approach mode cannot capture a glideslope that the procedure does not provide.
- Verify the frequency and course: Use the approach data available in the simulator rather than assuming both ends share the same settings.
- Check for a data mismatch: Changed runway numbers, older navigation data or third-party airport scenery can leave the localizer missing or displaced. Temporarily disabling the airport add-on can help identify an override conflict.
For a practical example, our guide to checking and flying an ILS in MSFS 2024 shows how to distinguish a full ILS from a localizer-only or non-ILS runway before beginning the approach.