Wednesday, January 23, 2008

AIRPORT LIGHTING


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 operated from dusk till dawn and 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 (visual flight rules minimums). However, there is no requirement for this, so a pilot has the responsibility of determining if the weather is VFR.

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, which produces the visual effect of flashes at regular intervals.
The combination of light colors from an airport beacon indicates the type of airport.

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 followed by a green flash identifies 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, which 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
Visual approach slope indicator (VASI) installations are the most common visual glidepath systems in use. The VASI provides obstruction clearance within 10° of the runway extended runway centerline, and to 4 nautical miles (NM) from the runway threshold. AVASI 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 which is normally set at 3°. The 3-bar system provides two glidepaths with the lower glidepath normally set at 3° and the upper glidepath one-fourth 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 having a white segment in the upper part of the beam and a red segment in the lower part of the beam.

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. A tri-color system consists of a single light unit projecting a three-color visual approach path. A below the glidepath indication is red, on the glidepath color is 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.

There are also pulsating systems, which consist of a single light unit projecting a two-color visual approach path. A below the glidepath indication is shown by a steady red light, slightly below is indicated by pulsating red, on the glidepath is indicated by a steady white light, and a pulsating white light indicates above the glidepath.

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
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. These lights are classified according to the intensity they are capable of producing. They are classified as high intensity runway lights (HIRL), medium intensity runway lights (MIRL), or 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.

IN-RUNWAY LIGHTING
Touchdown zone lights (TDZL), runway centerline lights (RCLS), and taxiway turnoff lights are installed on some precision runways to facilitate landing under adverse visibility conditions. TDZLs are two rows of transverse light bars disposed symmetrically about the runway centerline in the runway touchdown zone. RCLS consists of flush centerline lights spaced at 50-foot intervals beginning 75 feet from the landing threshold. Taxiway turnoff lights are flush lights, which emit a steady green color.

CONTROL OF AIRPORT LIGHTING
Airport lighting is controlled by air traffic controllers at controlled airports. At uncontrolled 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 uncontrolled airports, the pilot may control the lighting by using the radio. This is done by selecting a specified frequency and clicking the radio microphone.

For information on pilot controlled lighting at various airports, refer to the Airport/Facility Directory.

TAXIWAY LIGHTS
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 air traffic controller when deemed necessary or when requested by the pilot. Some airports also have taxiway centerline lights that are green in color.

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—either 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 Light— flashes high intensity white lights during the daytime with the intensity reduced for nighttime.
  • Dual Lighting—is a combination of flashing red beacons and steady red lights for nighttime operation, and high intensity white lights for daytime operations.
1 comments



Comments

1 comments to "AIRPORT LIGHTING"

Anonymous said...
July 5, 2012 at 12:36 AM

This description is way out of date and should be revised. I didn't read it all and gave up at the description of PAPI which is completely erroneous. TRY AGAIN.

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