Precision approach path indicator: Difference between revisions

Revision as of 15:52, 1 March 2023

Revision as of 15:58, 1 March 2023

Line 4:

[[Image:PAPI Jersey Airport.JPG|thumb|The PAPI can be seen to the right (non-standard) side of the runway. The aircraft is slightly below the glideslope.]]

A '''precision approach path indicator''' ('''PAPI''') is a system of [[Electric light|lights]] on the side of an airport [[runway]] threshold that provides visual [[descent (aircraft)|descent]] guidance information during [[final approach]]. It is generally located on the left-hand side of the runway approximately 300 meters beyond the landing threshold of the runway.

==Design and installation==

Line 19:

A color filter may not be necessary with colored LED lights.

A PAPI installation consists of a bar of four units. Units should be frangible but not susceptible to jet blast. The inner edge of the PAPI installation should be situated 15m15 meters from the runway edge, and not closer than 14m to any runway or taxiway. The units should be spaced 9m 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 10m from the runway edge.<ref name="ICAO"/> Units should be frangible but not susceptible to jet blast.

The PAPI isshould usuallybe located on the left-hand side of the runway at right angles to the runway center line., The units are spaced 9 meters apart with the nearest unit 15 meters from the runway edge. A PAPIalthough can, if required, 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.

The optimum distance from the runway threshold depends on the wheel clearance over the threshold of the types of aircraft expected to land on the runway; compatibility with non-visual glide paths such as ILS down to the minimum possible range and height; and any difference in elevation between the PAPI installation and the runway threshold. This optimum distance may be adjusted depending on runway length and obstacle clearance. Harmonisation between PAPIs and an ILS system must take into account the distance between eye height and ILS receiver height for various aircraft.<ref name="ICAO"/>{{rp|8-33}}

Line 36 ⟶ 38:

[[Image:PAPI M39.jpg|thumb|Individual precision approach path indicator]]

The PAPI is a light array positioned beside the [[runway]]. It normally consists of four equi-spaced light units color-coded to provide a visual indication of an aircraft's position relative to the designated [[glideslope]] for the runway. An abbreviated system (APAPI) consisting of two light units can be used for some categories of aircraft operations. The international standard for PAPI is published by the [[International Civil Aviation Organization]] (ICAO) in ''Aerodromes, Annex 14 to the Convention on International Civil Aviation, Volume 1, Chapter 5''. National regulations generally adopt the standards and recommended practices published by ICAO. An earlier glideslope indicator system, the [[visual approach slope indicator]] (VASI), only provided guidance down to heights of {{convert|60|m|ft|sigfig=1}} whereas PAPI provides guidance down to flare initiation (typically {{convert|15|m|ft|sigfig=1|disp=x|, or }}).{{cn|date=February 2023}}

PAPIs are calibrated relative to the Minimum Eye Height over Threshold (MEHT).<ref name="ICAO">{{cite book |title=ICAO Doc 9157, Aerodrome Design Manual. Fifth edition, 2021. Part 4, Visual Aids. Chapter 8 |publisher=ICAO |url=http://icscc.org.cn/upload/file/20220712/20220712090914_13813.pdf |access-date=1 March 2023}}</ref> For certain aircraft with a low pilot eye height, the pilot will see a "slightly low" indication even though they are on the ILS glideslope.<ref>https://publicapps.caa.co.uk/docs/33/CAP637%20Visual%20Aids%20Handbook.pdf</ref> Pilot eye height is usually above the ILS receiver antenna.<ref>https://www.airbus.com/sites/g/files/jlcbta136/files/2021-11/Airbus-Aircraft-Data-for-Visual-Aids-Calibration-v5.0.pdf</ref> [[Concorde]] had a particularly high eye height because the main undercarriage was so far behind the cockpit, so the pilots needed to land with a "slightly high" indication.<ref name="Bannister">{{cite book |last1=Bannister |first1=Mike |title=Concorde: The thrilling account of history’s most extraordinary airliner |date=29 September 2022 |publisher=Random House |isbn=978-0-241-55702-0 |url=https://www.google.com/books/edition/Concorde/QSthEAAAQBAJ |access-date=1 March 2023 |language=en}}</ref>

The PAPI is usually located on the left-hand side of the runway at right angles to the runway center line. The units are spaced 9 meters apart with the nearest unit 15 meters from the runway edge. A PAPI can, if required, be located on the right-hand side of the runway. 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.

The light characteristics of all light units are identical. In good visibility conditions the guidance information can be used at ranges up to {{convert|5|mi|km}} by day and night. At night the light bars can be seen at ranges of at least {{convert|20|mi|km}}.

Line 54 ⟶ 53:

PAPIs were used by NASA's Space Shuttle for its safe landing, for which Johnson was interviewed by UK local news media and TV.{{cn|date=March 2023}}

An earlier glideslope indicator system, the [[visual approach slope indicator]] (VASI), only provided guidance down to heights of {{convert|60|m|ft|sigfig=1}} whereas PAPI provides guidance down to flare initiation (typically {{convert|15|m|ft|sigfig=1|disp=x|, or }}).{{cn|date=February 2023}}

2008 saw the advent of new PAPI devices manufactured using solid state [[LED lamp]]s instead of [[incandescent lamp]]s. The LEDs produce sufficient brightness to satisfy ICAO light intensity and beamspread standards, and average lifetime with the LED based systems is 50,000 hours or more. By using LEDs, the device's power consumption is lowered considerably. The LED systems run internally on DC voltage, so the DC voltage requirements, along with the LEDs' inherently low power consumption, now allow for solar-powered PAPIs, enabling them to function completely independently of a power grid.<ref>{{cite web |url=http://www.flightlight.com/airportlighting/4.0.1/4.0.1.html |title=Solar PAPI & APAPI (Precision Approach Path Indicator) |access-date=2012-04-10 |url-status=dead |archive-url=https://web.archive.org/web/20111230132434/http://www.flightlight.com/airportlighting/4.0.1/4.0.1.html |archive-date=2011-12-30 }}</ref>