Learn what ILS approach lights show, how pilots use them at decision altitude, and when the lights permit continued descent or require a go-around.
ILS approach lights are a ground-lighting array extending outward from the runway threshold, usually along the extended centreline. Pilots use the pattern to identify the landing runway, judge alignment and transition from ILS instruments to outside visual references near decision altitude. The lights do not provide the ILS radio guidance.
In Aviation & Real-World Flying, the formal term is an approach lighting system, or ALS. “ILS approach lights” is common shorthand because precision runways often combine an ALS with an instrument landing system, but the two installations are separate.
Are approach lights part of the ILS?
No: the approach lighting system and the ILS are separate systems that work together during the final stage of an instrument approach.
| System | What it tells the pilot | What it does not provide |
|---|---|---|
| ILS localiser and glideslope | Lateral and vertical instrument guidance | A visual runway reference |
| Approach lighting system | Runway alignment, roll and distance cues before the threshold | Electronic course or glideslope guidance |
| PAPI or VASI | Visual indication of position above or below the approach path | Localiser guidance |
| Threshold, edge and touchdown-zone lights | The threshold, runway boundaries and landing area | Pre-threshold instrument guidance |
Approach lights help the pilot change from instrument references to a recognisable outside picture. Our broader explanation of runway, threshold and approach-light cues covers the lighting encountered after that transition.
How do pilots use ILS approach lights?
Pilots use the lights only after flying the published ILS accurately and confirming that the visual references are sufficient to continue safely and legally.
- Brief the lighting and minima. The approach chart identifies the runway, decision altitude or height, required visibility and missed-approach procedure. Lighting failures may change the applicable minima, so the crew checks operational information and any inoperative-components provisions. See our explanation of how to find minima and lighting information on an approach chart.
- Track the ILS on instruments. The pilot follows the localiser and glideslope while maintaining the correct speed, configuration and descent rate. Seeing lights early is not a reason to abandon instrument cross-checking; sim pilots can practise the complete localiser-to-visual ILS sequence.
- Identify a coherent pattern. A line or group of approach lights must agree with the expected runway centreline. An isolated light, nearby road or parallel runway is not enough.
- Assess the approach at decision altitude. The aircraft must be in a position from which landing can be made using normal manoeuvres, with the required visibility and visual references under the applicable rules.
- Continue or go around. If the references are adequate, the pilot transitions progressively to the runway picture while retaining an instrument cross-check. If they are not, the pilot starts the published missed approach at the decision point rather than descending while searching for more lights.
What do different approach-light patterns mean?
The pattern provides alignment, roll, distance and threshold cues; it does not encode landing instructions or replace an ATC clearance.
- White centreline lights or bars extend the runway centreline towards the arriving aircraft.
- Crossbars make bank and alignment errors easier to recognise and give the otherwise narrow pattern some scale.
- Sequenced flashing lights, informally called the rabbit, lead the eye towards the threshold. They do not mean that the runway is clear or that landing is authorised.
- Red side-row or terminating bars appear in some precision systems near the inner portion of the array. They have specific significance under certain visual-reference rules.
- Green threshold lights mark the runway threshold when viewed from the approach direction; they belong to the runway lighting rather than the radio ILS.
There is no single worldwide layout. Charts may identify systems such as ALSF, MALSR or a Calvert arrangement, each with a different combination of bars, centreline lights and flashers. Pilots brief the installed system instead of expecting every ILS runway to look alike.
Do approach lights alone permit descent below decision altitude?
Sometimes, but only to the limit allowed by the governing rules; merely seeing a flashing light does not automatically permit a landing.
For example, under US rules, an approach lighting system is an accepted visual reference when the other required conditions are met. If the ALS is the only visible reference, descent generally cannot continue below 100 feet above touchdown-zone elevation unless the red terminating bars or red side-row bars are distinctly visible. Another qualifying runway reference may also permit continuation.
Other authorities and operators use their own wording and approval requirements. CAT II and CAT III operations also involve specific aircraft, crew and ground-equipment approvals, so a CAT I rule must not be applied mechanically to them.
What happens if the approach lights are out?
An approach-light failure can increase the required visibility or make a particular set of minima unavailable, even when the localiser and glideslope remain fully operational.
The crew applies the chart’s inoperative-lighting provisions and operational rules before beginning or continuing the approach. PAPI, runway-edge lights or a working ILS cannot simply be treated as substitutes for a required ALS.
Maximum brightness is not always the clearest setting: intense lights can bloom in fog, heavy rain or snow. Where control arrangements and regulations permit, pilots may request a more suitable intensity. In a flight simulator, default airport scenery may simplify or omit the real pattern; for realistic practice, use the charted decision and go around if the simulated visual reference is inadequate.