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Encyclopedia > Precision Approach Path Indicator

The Precision Approach Path Indicator (PAPI) is a light system positioned beside the runway that consists of two, three, or four boxes of lights that provide a visual indication of an airplane's position on the glidepath for the associated runway. The FAA standard for the PAPI is the same as the ICAO's standard Visual Glide Slope Indicator. Aerial picture of a runway of Chennai International Airport, Tamil Nadu A runway is a strip of land on an airport, on which aircraft can take off and land. ... Glide-path typically refers to an aircraft’s angle of approach for landing at an airport’s runway. ... The Federal Aviation Administration is the entity of the United States government which regulates and oversees all aspects of civil aviation in the U.S. // Activities Along with the European Joint Aviation Authorities, the FAA is one of the two main agencies worldwide responsible for the certification of new aircraft. ... The International Civil Aviation Organization (ICAO), an agency of the United Nations, develops the principles and techniques of international air navigation and fosters the planning and development of international air transport to ensure safe and orderly growth. ... Wikipedia does not yet have an article with this exact name. ...

The PAPI is usually located on the left side of the runway and can be seen up to five miles during the day and twenty miles at night. It has two or four lights installed in a single row instead of far and near bars that would be characteristic of Visual Approach Slope Indicator (VASI).

Each box of lights is equipped with an optical apparatus that splits light output into two segments, red and white. Depending on the angle of approach, the lights will appear either red of white to the pilot. Ideally the total of lights will change from white to half red, moving in succession from right to left side. The pilot will have reached the normal glidepath (usually 3%) when there is an even split in red and white lights. If an airplane is beneath the glidepath, red lights will outnumber white; if an airplane is above the glidepath, more white lights are visible. An aviator is a person who flies aircraft for pleasure or as a profession. ...

During aircraft descent, this system, along with other airport lights, may be activated by the pilot by keying the airplane microphone with the airplane's communication radio tuned to the CTAF. A descent during air travel is any portion where an aircraft decreases altitude, and is the opposite of an ascent. ... CTAF, or Common Traffic Advisory Frequency, is the name given to a VHF radio frequency used at U.S. airports which do not have an active or on-site control tower, such as when some major airports close their tower overnight. ...

The PAPI operates on the principle of the Fresnel lens. Fresnel Lens displayed in a Paris museum A Fresnel lens is a type of lens invented by Augustin-Jean Fresnel. ...

See also

Pilot Controlled Lighting (PCL), also known as Aircraft Radio Control of Aerodrome Lighting (ARCAL) or Pilot Activated Lighting (PAL), is a technical system by which aircraft pilots can control the lighting of an airport or airfields runways and taxiways via radio. ... The Visual Approach Slope Indicator (VASI) is a system of lights on the side of a runway that provide visual descent guidance information during the approach to a runway. ... Runway End Identifier Lights (REIL) are installed at many airports to provide rapid and positive identification of the approach end of a particular runway. ... Runway Edge Lights are used to outline the edges of runways during periods of darkness or restricted visibility conditions. ...


  • FAA Aeronautical Information Manual: Visual Glideslope Indicators
  • FAA TERPS directive



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