RUNWAY LIGHTING SYSTEMS COMPLETE NOTES

RUNWAY EDGE LIGHTS

Runway edge lights define the lateral limits of the runway and help pilots identify the usable runway width. In FAA guidance they are classified by intensity:

• HIRL: High Intensity Runway Lights
• MIRL: Medium Intensity Runway Lights
• LIRL: Low Intensity Runway Lights

FAA guidance states that they are normally white, with yellow replacing white on the last 2,000 ft or half the runway length, whichever is less, on instrument runways. ICAO Annex 14 uses a different rule: the section 600 m or one-third of the runway length, whichever is less, at the remote end (from where the take-off run starts) shows yellow, and the lights between the runway start and a displaced threshold show red in the approach direction. Indian aerodromes follow ICAO-based provisions, so check the applicable AIP before assuming the FAA distance.

Study method: Runway Edge → Lateral Limits → White. The intensity classification tells you the system's intensity level, while the colour provides visual runway guidance.

Runway lights are normally supplied from CCR-fed series circuits through isolation transformers; see Note 05, Note 07 and Note 08.

THRESHOLD LIGHTS

Threshold lights identify the beginning of the landing portion of the runway for an approaching aircraft. For FAA configurations they are green when viewed from the approach side.

ICAO Annex 14 specifies threshold lights as fixed, unidirectional green lights in a line at right angles to the runway axis at the threshold (at the displaced threshold where one exists). Wing bars, extra green lights on each side of the threshold, may be added for conspicuity, particularly on precision approach runways. The FAA achieves the same result with bidirectional green/red fixtures (see runway end lights below).

Study the threshold as both a physical runway reference point and a visual lighting indication.

RUNWAY END LIGHTS

Runway end lighting identifies the end of the usable runway. FAA practice uses bidirectional fixtures whose colour depends on viewing direction, so one fixture serves as the threshold light for one direction and the end light for the other:

ICAO Annex 14 specifies runway end lights as fixed, unidirectional red lights visible in the direction of the runway, in a line at right angles to the axis, consisting of at least six lights. ICAO threshold (green) and end (red) lights may be separate or combined in one fixture. Where a stopway is provided, ICAO also specifies stopway lights: fixed, unidirectional red lights facing the runway.

Memory link: think of the runway-end fixture as a bidirectional visual indication, not one colour from every direction.

RUNWAY CENTRELINE LIGHTS

Centreline lights provide accurate runway alignment and a distance-remaining cue in the final part of the runway, particularly in reduced visibility. They are required on CAT II and CAT III precision approach runways and may be provided on other runways, for example where RVR for take-off is low.

Spacing: FAA centreline lights are spaced at 50 ft (15 m). ICAO specifies approximately 15 m, and approximately 30 m is permitted on runways intended for use in RVR conditions of 350 m or greater.

Centreline colour sequence (FAA and ICAO)

Viewed from the landing threshold toward the far end: White → Alternating Red/White → Red. The FAA and ICAO sequences are essentially the same pattern, because 3,000 ft ≈ 914 m and 1,000 ft ≈ 305 m. Only the units and rounding differ.

Always identify what the question is asking for: FAA requirement? ICAO requirement? Indian AIP? Airport specification? Project-specific requirement? This distinction is particularly important in examinations and technical documentation.

TOUCHDOWN ZONE LIGHTS (TDZL)

TDZL provide visual identification of the touchdown zone on applicable precision approach runways. FAA guidance describes rows of transverse light bars symmetrically disposed around the centreline, using steady-burning white lights, giving a clear indication of the touchdown-zone area during landing.

Extent: FAA TDZL start 100 ft (30 m) beyond the threshold and extend to 3,000 ft (900 m) from the threshold, or to the runway midpoint where the runway is shorter than 6,000 ft (1,800 m). ICAO Annex 14 uses the same 900 m / midpoint rule, with short barrettes of three fixed white lights. TDZL are unidirectional, facing the landing threshold, and are required on CAT II and CAT III runways.

REIL

Runway End Identifier Lights. REILs are a pair of synchronised white flashing lights, one on each side of the runway at the threshold and facing the approach, giving rapid and positive identification of the approach end of a runway. They are especially useful where the runway has little contrast with surrounding terrain or lights, or in reduced visibility. ICAO calls the equivalent aid runway threshold identification lights (white flashing, 60 to 120 flashes per minute).

Do not confuse REIL with the runway-end lights themselves. Despite the name, REIL marks the approach end (threshold) of the runway, not the far end. It is a separate visual aid, white and flashing, intended specifically for rapid identification of the runway being approached.

RETIL

Rapid Exit Taxiway Indicator Lights. RETILs give distance-to-go information to the nearest rapid exit taxiway and can improve situational awareness during landing and rollout in applicable low-visibility or heavy-traffic conditions.

RETIL is an ICAO Annex 14 aid. The lights are fixed, unidirectional yellow lights installed in the runway next to the centreline, on the same side as the associated rapid exit taxiway. They form a 3-2-1 sequence of sets about 100 m apart (six lights in total), counting down to the point of tangency of the exit taxiway centreline. ICAO recommends them on runways intended for use in RVR below 350 m and/or where traffic density is heavy. Check the aerodrome's AIP entry to see whether RETILs are installed on a given runway.

RUNWAY LIGHTING QUICK REVISION TABLE

Function-based revision

Remembering the purpose of each system is often easier than memorising colours alone.

EXAM QUESTIONS

FINAL STUDY TAKEAWAY

Do not study runway lighting as a list of colours. Study every system through Location → Colour → Function → Operational Meaning, then connect it to the applicable FAA, ICAO, AIP, airport or project requirement.

ENGINEERING & EXPERT NOTES

REFERENCES & FURTHER READING

These notes are a study aid. Verify details against the primary sources below.

EXPLORE ALL AGL STUDY NOTES