Airports' Approach Lights: A Necessary Investment?

Runway approach lights are a crucial component of aviation ground lighting, enabling pilots to visually identify the runway environment and align their aircraft for landing. The design and installation of these lighting systems can be a significant investment for airports, but they are essential for ensuring safe aircraft operations, especially during periods of reduced visibility. The specific requirements and configurations of approach lighting systems vary depending on factors such as the airport's licensing category, the volume of air traffic, and the need to support operations in low-visibility conditions.

Runway Approach Lighting Systems

The length of the light system, the number of lights, and the spacing between them depend on the type of ALS, the lights used (separate light sources or barettes), and whether the system meets the required serviceability levels specified in ICAO Annex 14. Simple ALS for non-instrument runways and non-precision approach runways typically consist of a row of lights extending at least 420 metres from the threshold, with a crossbar at 300 metres. More advanced systems, such as the CAT I, II, and III lighting systems, feature longer rows of lights, additional light sources, and more crossbars.

The brightness of the lights can be adjusted for day and night operations and may be controlled by the Air Traffic Control Tower (ATCT) or, in some cases, by the pilot via radio.

Several ALS configurations are recognised by the International Civil Aviation Organization (ICAO), and non-standard configurations are also installed at some airports. Typically, approach lighting systems are of high intensity and are complemented by various on-runway light systems, such as runway end identifier lights (REIL), touchdown zone lights (TDZL), and high-intensity runway lights (HIRL).

Approach lighting systems play a crucial role in ensuring safe aircraft operations by aiding pilots in judging distance and alignment for landing.

Runway End Identifier Lights (REIL)

The REIL system provides three intensity settings and has an approximate range of three miles in daylight and twenty miles at night. The lights flash between 60 and 120 times per minute and are visible only in the direction of the runway approach. The system can be controlled by the air traffic control tower, remotely by the pilot, or manually from the control cabinet.

REILs are compatible with most approach systems, such as ALSF, SSALR, and MALSR. The installation of these lights is recommended by the International Civil Aviation Organization (ICAO) under certain conditions, such as when additional threshold conspicuity is necessary or when a runway threshold is displaced from its normal position.

Runway Edge Lights

Runway edge lighting systems are classified by how bright the lights can get. The brightest lights are High-Intensity Runway Lights (HIRL), followed by Medium-Intensity Runway Lights (MIRL), and then Low-Intensity Runway Lights (LIRL). The HIRL and MIRL systems have variable intensity controls, whereas the LIRLs normally have one intensity setting.

The runway edge lights are white, except on instrument runways where yellow replaces white on the last 2,000 feet or half the runway length, whichever is less, to form a caution zone for landings.

The lights marking the ends of the runway emit red light toward the runway to indicate the end of the runway to a departing aircraft and emit green outward from the runway end to indicate the threshold to landing aircraft.

The maximum spacing between runway edge lights is 200 feet, and they are 2 to 10 feet from the edge of the usable runway.

Understanding runway lights is essential for safe flying. These lights not only allow precise takeoffs and landings in bad weather or at night but also help keep aircraft moving safely on the airport surface.

Runway Centerline Lighting Systems

The lights start from 75 feet from the landing threshold and extend to within 75 feet of the end of the runway. The lights themselves are spaced at 50-foot intervals. When viewed from the landing threshold, the runway centerline lights are white until the last 3,000 feet of the runway. The white lights begin to alternate with red for the next 2,000 feet, and for the last 1,000 feet of the runway, all centerline lights are red. If the runway centerline lights are spaced at 25-foot intervals, alternate pairs of red and white lights should be used on the section from 3,000 to 1,000 feet from the runway end. Where the runway is less than 6,000 feet in length, the alternate red and white lights extend from the midpoint of the runway usable for landing to 1,000 feet from the runway end.

Runway centerline lights and touchdown zone lights are required for CAT II and CAT III runways, and for CAT I runways used for landing operations below 2,400 feet RVR. Runway centerline lights are also required on runways used for takeoff operations below 1,600 feet RVR unless specifically approved by the FAA in an airline operator's specification for that runway.

Approach Lighting Systems (ALS)

The required minimum visibilities for instrument approaches are influenced by the presence and type of approach lighting system. For example, in the US, a CAT I ILS approach without approach lights will have a minimum required visibility of 3/4 mile, or 4000 feet of runway visual range. With a 1400-foot or longer approach light system, the minimum potential visibility might be reduced to 1/2 mile (2400 feet of runway visual range).

ALS are illuminated during hours of darkness and/or when the visibility is less than that required for visual flight rules. There are several types of ALS, including:

• Medium-Intensity Approach Lighting System (MALS)
• Medium-Intensity Approach Lighting System with Sequenced Flashers (MALSF)
• High-Intensity Approach Lighting System with Sequenced Flashing Lights (ALSF-2)
• Simplified Short Approach Lighting System with Sequenced Flashers (SSALF)
• Runway End Identifier Lights (REIL)
• Visual Approach Slope Indicator (VASI)

ALS provides the basic means to transition from instrument flight to visual flight for landing. Operational requirements dictate the sophistication and configuration of the approach light system for a particular runway.

Frequently asked questions