Threshold Lights are green lights that mark the runway's starting edge , where aircraft are permitted to land. They are a crucial part of the landing lights and help pilots identify the safe landing zone , especially in nighttime or low-visibility conditions .
1. Features of Threshold Lights
✅ Placed at the threshold of the runway → Usually in a line across the entire width of the runway.
✅ Green lights → Visible from the approach direction , so pilots know where they can land.
✅ Can be bidirectional → On the other side they can be red , to indicate the end of the track.
✅ Part of the Runway Lighting System → Works with Runway Edge Lights, REIL and Approach Lights .
✅ Works in any visibility level → Essential for night landings and ILS-assisted landings .
2. Function of Threshold Lights
🔹 Clear marking of the landing point → Pilots know exactly where the safe landing zone begins.
🔹 Prevents early landings → Prevents planes from accidentally landing too short .
🔹 Essential in poor visibility → Helps pilots in fog, rain or night operations.
💡 Important:
- Green side → Visible to incoming aircraft wanting to land.
- Red side → Visible to aircraft on the ground , marks the end of the runway .
3. Difference between Threshold Lights and other landing lights
| Lighting system | Location | Goal | Colour |
|---|---|---|---|
| Threshold Lights | At the beginning of the runway | Marks the safe landing area | Green (from the air), Red (from the runway) |
| Runway End Identifier Lights (REIL) | On either side of the threshold | Flashing lights to identify the runway | White flashing |
| Runway Edge Lights | Along the edges of the runway | Marks the track boundary | White → Yellow → Red |
| Runway Centerline Lights | Middle of the runway | Helps with alignment during landing and take-off | White → White/Red → Red |
4. Types of Threshold Lighting
📌 Standard Threshold Lights → Most common, green lights in a straight line.
📌 Bidirectional Threshold/Runway End Lights → Green for landing direction, red for runway end.
📌 Enhanced Threshold Lighting → Combined with REIL (Runway End Identifier Lights) for better visibility.
5. Where are Threshold Lights used?
📍 All commercial airports → Essential for airports large and small .
📍 Military airfields → Extra clear for nighttime and low-visibility operations.
📍 Emergency landing strips and short runways → Critical for precision landings.
💡 In short:
Threshold Lights are green lights that mark the beginning of the runway . They help pilots position themselves correctly for landing and prevent landings that are too short . In bidirectional systems, they are green for approaching aircraft and red for aircraft on the runway , warning of the end of the runway.