Precision approach path indicator: Difference between revisions

Revision as of 00:51, 19 November 2023

Revision as of 16:34, 12 December 2023

Line 11:

1 = Axis datum<br />2 = Light source<br />3 = Red filter<br />4 = Lenses<br />5 / 6 = Light beam- white/red]]

Optical construction:

* 2Two lamps for redundancy;

* Anodized aluminium reflectors.;

* Red color filter.;

* 1One or 2two lenses.;

* Lamps and reflectors replaceable without recalibration.

Each light unit consists of one or more light sources, red filters and lenses. A color filter may not be necessary with colored LED lights. Each light unit emits a high-intensity beam. The lower segment of the beam is red, and the upper part is white. The transition between the two colours must take place over an angle not greater than three minutes of arc. This characteristic makes the color change very conspicuous, a key feature of the PAPI signal. To form the PAPI guidance signal, the color transition boundaries of the four units are fixed at different angles. The lowest angle is used for the unit furthest from the runway, the highest for the unit nearest to the runway. The designated glideslope is midway between the second and third light unit settings.

A PAPI installation consists of a bar of four units. Units should be [[Frangibility|frangible]] but not susceptible to jet blast. The inner edge of the PAPI installation should be situated 15 meters from the runway edge, and not closer than 14m14 meters to any runway or taxiway. The units should be spaced 9m9 meters apart. An abbreviated system, A-PAPI, can be used for some categories of aircraft operations. It consists of two units with the inner unit located 10m10 meters from the runway edge.<ref name="ICAO"/>

The PAPI should be located on the left-hand side of the runway at right angles to the runway center line, although can be located on the right-hand side of the runway if required. The red lights are always on the side closest to the runway. If the PAPI is on the right-hand side of the runway (non-standard), the red lights will be on the left. At some locations PAPIs are installed on both sides of the runway but this level of provision is beyond the requirements of ICAO.