Does bad weather affect ILS signals and approaches?

Bad weather usually does not weaken an ILS signal: fog, cloud and ordinary rain have little effect on its VHF localiser and UHF glideslope transmissions. It can still make the approach much harder through low visibility, wind, turbulence, icing and poor braking, while snow or nearby traffic may indirectly disturb guidance.

For Aviation & Real-World Flying, the useful distinction is between signal integrity and approach safety. An ILS may remain accurate while the aeroplane is close to its wind, visibility or runway-state limits.

Can rain, fog or snow interfere with an ILS?

Fog and cloud do not block an ILS, and rain attenuation is normally negligible at ILS frequencies over the short line-of-sight distance involved.

The localiser and glideslope are separate ground transmissions. Our explanation of the beam geometry behind localiser and glideslope indications shows why poor visibility does not prevent radio guidance from reaching the aircraft.

Why can ILS needles move in poor visibility?

Transient ILS movement in bad weather is more often caused by objects near the antennas than by the weather itself.

• Aircraft and vehicles: A large object entering an ILS critical or sensitive area can reflect or distort the signal, particularly the glideslope.
• Snow accumulation: Deep or uneven snow around some ground installations can alter the reflecting environment and course structure.
• Buildings and construction: Cranes, temporary structures and new development can produce multipath reflections.
• Equipment faults: A ground transmitter or its monitor can fail. Certified installations are monitored, and an out-of-tolerance condition normally raises an alarm or removes the affected component from service.
• Cockpit setup errors: A wrong frequency, wrong runway end, incorrect navigation source or an intercept from unsuitable geometry can look like weather interference.

Low-visibility procedures keep aircraft and vehicles farther from protected ILS areas. This explains why interference and poor weather may appear related: the weather prompts extra protection, but it is the reflecting object—not the fog—that bends the beam.

Most consumer flight simulators do not model meaningful rain fade or changing snow depth around an ILS installation. If guidance disappears after changing the weather preset, first check the frequency, runway, navigation source, approach geometry and any scenery or navigation-data mismatch.

How does bad weather change an ILS approach?

Bad weather reduces handling and decision margins even when the localiser and glideslope remain perfectly serviceable.

• Crosswind: The localiser shows the extended centreline, but the pilot or autopilot must apply the necessary wind correction. Strong gusts can cause repeated deviations without indicating a faulty signal.
• Turbulence and windshear: Rapid airspeed and flight-path changes can make the approach unstable. An ILS does not detect or avoid a microburst.
• Icing: Airframe ice increases drag and reduces aerodynamic performance. Anti-ice use and any speed adjustment must follow the aircraft's approved procedure.
• Low visibility: The approach must comply with its published decision altitude or decision height, visibility requirements and the applicable operating rules.
• Runway contamination: ILS guidance ends at the runway; it does not guarantee adequate landing distance or directional control on water, slush, snow or ice.
• Cold temperature: The radio glideslope angle does not change, but barometric procedure altitudes can require published cold-temperature corrections under local rules.

Before deciding whether conditions are suitable, decode the visibility, wind, cloud and precipitation in the METAR. We also cover the broader aircraft-performance penalties caused by wind, temperature and weather.

Can an ILS land an aircraft in zero visibility?

An ILS can support very-low-visibility operations, but it does not automatically permit every aircraft to land in zero visibility.

CAT II and CAT III operations require the appropriate ground equipment, runway lighting, aircraft systems, crew qualification, operator approval and low-visibility procedures. Some authorised CAT III operations use no decision height, but runway visual range and system requirements still apply; “zero visibility” is not a general capability.

For a conventional approach, the required visual reference must be available by the applicable decision altitude or height. If it is not, the correct response is the published missed approach—even with centred needles or an engaged autopilot.

What should you do if ILS guidance becomes unreliable?

Treat unexplained flags, identification loss or conflicting guidance as a navigation failure rather than assuming that rain is disrupting the signal.

1. Confirm serviceability. Check the approach chart, reported facility status and station identification. In a simulator, verify that the selected approach matches the installed airport and navigation data.
2. Check the setup. Confirm the localiser frequency, inbound course and navigation source. Intercept the localiser first and approach the normal glideslope from below; capturing an upper false glideslope is possible when descending onto it from above.
3. Cross-check the indications. Compare raw ILS guidance with altitude, distance, heading and any independent navigation source. Do not chase a rapidly oscillating needle.
4. Assess approach stability. A valid ILS signal does not override wind limits, windshear warnings, excessive deviations or the aircraft's stabilised-approach criteria.
5. Go around when required. Discontinue the approach if guidance is flagged or unreliable, the aircraft becomes unstable, or the required visual reference is absent at minima.