Precision approach path indicator: Difference between revisions

Revision as of 15:22, 1 March 2023

Revision as of 15:27, 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]]s 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==

Line 21:

==Interpretation==

[[File:comparison_visual_landing_systems.svg|thumb|250px|Comparison of [[Precision approach path indicator|PAPI]], [[Visual approach slope indicator|VASI]], and [[Optical landing system|OLS]] meatball and datum lights {{nowrap|(not to scale)}}]]

The ratio of white to red lights seen is dependent on the angle of approach to the runway. Above the designated [[glide slope]] a pilot will observe more white lights than red; at approaches below the ideal angle more red lights than white will be seen. ForAt the optimum approach angle the ratio of white to red lights will remainbe equal throughout, for most aircraft, the exceptions being the [[Boeing 747]] and now retired [[Concorde]]. With the 747, because the cockpit is approximately 20 feet behind the nose and much higher than other aircraft, the flight crew in a 747 will typically see one red and three white lights when they are on the glide slope. The aircrew of Concorde would see four white lights as the Concorde's approach angle was higher than traditional aircraft.{{cn|date=February 2023}}

The greater number of red lights visible compared with the number of white lights visible in the picture means that the aircraft is flying below the glide slope. To use the guidance information provided by the aid to follow the correct glide slope a pilot would manoeuvre the aircraft to obtain an equal number of red and white lights.

Line 34:

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 Pilotsname="ICAO">{{cite inbook |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 maywith 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> when pilotPilot 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.