Airport Lighting | Flight-Study

The majority of airports have some type of lighting for night operations. The variety and type of lighting systems depends on the volume and complexity of operations at a given airport. Airport lighting is standardized so that airports use the same light colors for runways and taxiways.

Airport Beacon

Airport beacons help a pilot identify an airport at night. The beacons are normally operated from dusk until dawn. Sometimes they are turned on if the ceiling is less than 1,000 feet and/or the ground visibility is less than 3 statute miles (VFR minimums). However, there is no requirement for this, so a pilot has the responsibility of determining if the weather meets VFR requirements. The beacon has a vertical light distribution to make it most effective from 1–10° above the horizon, although it can be seen well above or below this spread. The beacon may be an omnidirectional capacitor-discharge device, or it may rotate at a constant speed, that produces the visual effect of flashes at regular intervals. The combination of light colors from an airport beacon indicates the type of airport. [Figure 1]

Figure 1. Airport rotating beacons

Some of the most common beacons are:

Flashing white and green for civilian land airports
Flashing white and yellow for a water airport
Flashing white, yellow, and green for a heliport
Two quick white flashes alternating with a green flash identifying a military airport

Approach Light Systems

Approach light systems are primarily intended to provide a means to transition from instrument flight to visual flight for landing. The system configuration depends on whether the runway is a precision or nonprecision instrument runway. Some systems include sequenced flashing lights that appear to the pilot as a ball of light traveling toward the runway at high speed. Approach lights can also aid pilots operating under VFR at night.

Visual Glideslope Indicators

Visual glideslope indicators provide the pilot with glidepath information that can be used for day or night approaches. By maintaining the proper glidepath as provided by the system, a pilot should have adequate obstacle clearance and should touch down within a specified portion of the runway.

Visual Approach Slope Indicator (VASI)

VASI installations are the most common visual glidepath systems in use. The VASI provides obstruction clearance within 10° of the extended runway centerline and up to four nautical miles (NM) from the runway threshold.

The VASI consists of light units arranged in bars. There are 2-bar and 3-bar VASIs. The 2-bar VASI has near and far light bars and the 3-bar VASI has near, middle, and far light bars. Two-bar VASI installations provide one visual glidepath that is normally set at 3°. The 3-bar system provides two glidepaths, the lower glidepath normally set at 3° and the upper glidepath ¼ degree above the lower glidepath.

The basic principle of the VASI is that of color differentiation between red and white. Each light unit projects a beam of light, a white segment in the upper part of the beam and a red segment in the lower part of the beam. The lights are arranged so the pilot sees the combination of lights shown in Figure 2 to indicate below, on, or above the glidepath.

Figure 2. Two-bar VASI system

Other Glidepath Systems

A precision approach path indicator (PAPI) uses lights similar to the VASI system, except they are installed in a single row, normally on the left side of the runway. [Figure 3]

Figure 3. Precision approach path indicator for a typical 3° glide slope

A tri-color system consists of a single-light unit projecting a three-color visual approach path. Below the glidepath is indicated by red, on the glidepath is indicated by green, and above the glidepath is indicated by amber. When descending below the glidepath, there is a small area of dark amber. Pilots should not mistake this area for an “above the glidepath” indication. [Figure 4]

Figure 4. Tri-color visual approach slope indicator

Pulsating VASIs normally consist of a single-light unit projecting a two-color visual approach path into the final approach area of the runway upon which the indicator is installed. The “on glidepath” indication is a steady white light. The “slightly below glidepath” indication is a steady red light. If the aircraft descends further below the glidepath, the red light starts to pulsate. The “above glidepath” indication is a pulsating white light. The pulsating rate increases as the aircraft gets further above or below the desired glideslope. The useful range of the system is about four miles during the day and up to ten miles at night. [Figure 5]

Figure 5. Pulsating visual approach slope indicator

Runway Lighting

There are various lights that identify parts of the runway complex. These assist a pilot in safely making a takeoff or landing during night operations.

Runway End Identifier Lights (REIL)

Runway end identifier lights (REIL) are installed at many airfields to provide rapid and positive identification of the approach end of a particular runway. The system consists of a pair of synchronized flashing lights located laterally on each side of the runway threshold. REILs may be either omnidirectional or unidirectional facing the approach area.

Runway Edge Lights

Runway edge lights are used to outline the edges of runways at night or during low visibility conditions. [Figure 6] These lights are classified according to the intensity they are capable of producing: high intensity runway lights (HIRL), medium intensity runway lights (MIRL), and low intensity runway lights (LIRL). The HIRL and MIRL have variable intensity settings. These lights are white, except on instrument runways where amber lights are used on the last 2,000 feet or half the length of the runway, whichever is less. The lights marking the end of the runway are red.

Figure 6. Runway lights

In-Runway Lighting

Runway centerline lighting system (RCLS) – installed on some precision approach runways to facilitate landing under adverse visibility conditions. They are located along the runway centerline and 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. For the remaining 1,000 feet of the runway, all centerline lights are red.

Touchdown zone lights (TDZL) – installed on some precision approach runways to indicate the touchdown zone when landing under adverse visibility conditions. They consist of two rows of transverse light bars disposed symmetrically about the runway centerline. The system consists of steady-burning white lights that start 100 feet beyond the landing threshold and extend to 3,000 feet beyond the landing threshold or to the midpoint of the runway, whichever is less.

Taxiway centerline lead-off lights – provide visual guidance to persons exiting the runway. They are color-coded to warn pilots and vehicle drivers that they are within the runway environment or ILS critical area, whichever is more restrictive. Alternate green and yellow lights are installed, beginning with green, from the runway centerline to one centerline light position beyond the runway holding position or ILS critical area holding position.

Taxiway centerline lead-on lights – provide visual guidance to persons entering the runway. These “lead-on” lights are also color-coded with the same color pattern as lead-off lights to warn pilots and vehicle drivers that they are within the runway environment or ILS critical area, whichever is more conservative. The fixtures used for lead-on lights are bidirectional (i.e., one side emits light for the lead-on function while the other side emits light for the lead-off function). Any fixture that emits yellow light for the lead-off function also emits yellow light for the lead-on function.

Land and hold short lights – used to indicate the hold short point on certain runways which are approved for LAHSO. Land and hold short lights consist of a row of pulsing white lights installed across the runway at the hold short point. Where installed, the lights are on anytime LAHSO is in effect. These lights are off when LAHSO is not in effect.

Control of Airport Lighting

Airport lighting is controlled by ATC at towered airports. At nontowered airports, the lights may be on a timer, or where an FSS is located at an airport, the FSS personnel may control the lighting. A pilot may request various light systems be turned on or off and also request a specified intensity, if available, from ATC or FSS personnel. At selected nontowered airports, the pilot may control the lighting by using the radio. This is done by selecting a specified frequency and clicking the radio microphone. [Figure 7] For information on pilot controlled lighting at various airports, refer to the Chart Supplement U.S. (formerly Airport/Facility Directory).

Figure 7. Radio controlled runway lighting

Taxiway Lights

Similar to runway lighting, taxiways also have various lights which help pilots identify areas of the taxiway and any surrounding runways.

Omnidirectional

Omnidirectional taxiway lights outline the edges of the taxiway and are blue in color. At many airports, these edge lights may have variable intensity settings that may be adjusted by an ATC when deemed necessary or when requested by the pilot. Some airports also have taxiway centerline lights that are green in color.

Clearance Bar Lights

Clearance bar lights are installed at holding positions on taxiways in order to increase the conspicuity of the holding position in low visibility conditions. They may also be installed to indicate the location of an intersecting taxiway during periods of darkness. Clearance bars consist of three in-pavement steady-burning yellow lights.

Runway Guard Lights

Runway guard lights are installed at taxiway/runway intersections. They are primarily used to enhance the conspicuity of taxiway/runway intersections during low visibility conditions, but may be used in all weather conditions. Runway guard lights consist of either a pair of elevated flashing yellow lights installed on either side of the taxiway, or a row of in-pavement yellow lights installed across the entire taxiway, at the runway holding position marking.

Note: Some airports may have a row of three or five in-pavement yellow lights installed at taxiway/runway intersections. They should not be confused with clearance bar lights described previously in this article.

Stop Bar Lights

Stop bar lights, when installed, are used to confirm the ATC clearance to enter or cross the active runway in low visibility conditions (below 1,200 ft Runway Visual Range (RVR)). A stop bar consists of a row of red, unidirectional, steady-burning in-pavement lights installed across the entire taxiway at the runway holding position, and elevated steady-burning red lights on each side. A controlled stop bar is operated in conjunction with the taxiway centerline lead-on lights which extend from the stop bar toward the runway. Following the ATC clearance to proceed, the stop bar is turned off and the lead-on lights are turned on. The stop bar and lead-on lights are automatically reset by a sensor or backup timer.

Obstruction Lights

Obstructions are marked or lighted to warn pilots of their presence during daytime and nighttime conditions. Obstruction lighting can be found both on and off an airport to identify obstructions. They may be marked or lighted in any of the following conditions.

Red obstruction lights – flash or emit a steady red color during nighttime operations, and the obstructions are painted orange and white for daytime operations.
High intensity white obstruction lights – flash high intensity white lights during the daytime with the intensity reduced for nighttime.
Dual lighting – a combination of flashing red beacons and steady red lights for nighttime operation and high intensity white lights for daytime operations.

New Lighting Technologies

A top priority of the FAA is to continue to enhance airport safety while maintaining airport capacity. Reducing runway incursions is a major component of this effort. Runway incursions develop quickly and without warning during routine traffic situations on the airport surface, leaving little time for corrective action. The Runway Status Lights (RWSL) System is designed to provide a direct indication to you that it is unsafe to enter a runway, cross a runway, or takeoff from or land on a runway when the system is activated.

Runway status lights are red in color and indicate runway status only; they do not indicate clearance to enter a runway or clearance to takeoff. The RWSL system provides warning lights on runways and taxiways, illuminating when it is unsafe to enter, cross, or begin takeoff on a runway. Currently, there are two types: Runway Entrance Lights (REL) and Takeoff Hold Lights (THL). [Figures 8 and 9]

Figure 8. Runway Entrance Lights (REL)

Figure 9. Takeoff Hold Lights (THL)

REL provide a warning to aircraft crossing or entering a runway from intersecting taxiways that there is conflicting traffic on the runway. THL provide a warning signal to aircraft in position for takeoff that the runway is occupied and it is unsafe to take off. As of 2016, the RWSL system is operational at 14 of the nation’s busiest airports with 3 more airports scheduled to receive the system by 2017.