Aerodrome lighting

Approach light systems

Length and pattern support alignment and the visual transition.

Simple and precision systems

A simple approach light system normally extends at least 420 m from threshold with a crossbar at 300 m, using the prescribed centreline arrangement. It supports non-instrument and non-precision operations where installed under the relevant criteria. The simple system can use single sources or barrettes as specified.

A CAT I precision approach system normally extends 900 m with the prescribed centreline and crossbar pattern, including a crossbar at 300 m. Basic arrangements use coded numbers of lights by distance or barrettes and supplementary crossbars as specified. CAT II/III systems add closely spaced centreline/barrettes, crossbars and red side-row lighting in the inner portion; the inner 300 m is particularly important for the low-height visual picture.

Installation and availability

The approach light system is referenced to the actual landing threshold, including a displaced threshold. A relocated threshold therefore changes the relevant visual geometry; runway pavement behind the original end is not an alternative visual datum. Elevated lights in aircraft operating areas must meet frangibility and mechanical safety requirements.

An aerodrome beacon supports locating the aerodrome where required by night use, poor conspicuity or surrounding conditions; a land aerodrome beacon typically alternates white and green. Ground lights must be made available with the applicable operational schedule; lights switched off because no operation is likely must be capable of being brought into operation at least one hour before expected arrival. After take-off, a controlled aerodrome retains lighting as needed for an emergency return; without ATC or central control, the relevant runway lighting remains for the reactivation period and at least 15 minutes after take-off. Local pilot-controlled lighting has published activation arrangements.

PAPI: compare eye path with the runway

Red and white describe the viewing angle to the light units.

Four units, one slope

A PAPI wing bar normally has four units, usually on the left of the runway unless otherwise arranged. Two white and two red indicate the nominal approach slope; more white means higher, more red lower. Four white is well above and four red well below. APAPI uses two units, one white/one red on slope.

The red/white transition comes from the light optics and viewing angle; the units do not measure aircraft altitude and change colour electronically for each aircraft. Eye-to-wheel height and the approved installation geometry affect wheel clearance. A PAPI indication does not by itself prove obstacle clearance outside the protected approach sector or compliance with an instrument procedure.

Cross-check rather than chase

Use the visual path with the aircraft’s approved technique, runway picture and instrument guidance. Published differences between ILS and PAPI slopes or displaced-threshold geometry can explain a mismatch. Avoid abrupt corrections close to the ground; continue only within the safe stabilised-approach criteria.

The slider changes the observer angle continuously and shows each light’s optical transition. The model explicitly illustrates eye-path angle rather than pretending that a four-light display gives a complete landing performance assessment.

Runway and taxiway light colours

Position and direction determine which colour is visible.

Runway system

Runway edge lights are normally white, with yellow in the caution zone near the far end on an instrument runway as specified. Threshold lights show green toward the approach; runway-end lights show red toward the runway. Centreline lights are white until the final 900 m, alternate red/white from 900 to 300 m remaining and red in the last 300 m, subject to shorter-runway provisions. Touchdown-zone lights are white barrettes.

Runway lead-in systems use the prescribed groups of flashing lights to guide an approach path. Stopway lights show red in the appropriate direction. Lights can be directional and intensity-adjustable: seeing a different colour from the opposite direction is intentional, not necessarily a failure.

Taxi guidance and stop signals

Taxiway edge lights are blue and centreline lights green, with prescribed green/yellow alternation in runway exit/critical-area arrangements. Stop bars are red across the taxiway; do not cross an illuminated bar. Runway guard lights flash yellow to warn of a runway holding position. Intermediate holding lights are fixed yellow; road holding lights give the prescribed red/green vehicle indication where installed.

The light pattern is a positive cue but must agree with the chart, signs, markings and clearance. A failed or unlit light does not itself authorise entry. Report a conflict and request clarification rather than selecting whichever cue allows movement.

Can you apply the rules?

Four original questions. Choose from the facts, then review the explanation.