Precision approach path indicator: Difference between revisions

Revision as of 16:34, 12 December 2023

Revision as of 13:13, 13 April 2024

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{{Short description|Visual aid in aviation}}

{{RefimproveMore citations needed|date=December 2009}}

[[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.]]

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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.

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|8-338–33}}

For a typical 3 degree approach slope, PAPI lights should be angled as follows: 3°30', 3°10', 2°50', 2°30' (3.50°, 3.17°, 2.83°, 2.50°).<ref name="ICAO"/>{{rp|8-368–36}}

==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 see more white lights than red; below the ideal angle more red lights than white will be seen. At the optimum approach angle the ratio of white to red lights will be equal, for most aircraft.

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The precision approach path indicator system was first devised in 1974 by Tony Smith and David Johnson at the [[Royal Aircraft Establishment]] in Bedford, England. It took them a further two years to fully develop the technology. Engineering firm Research Engineers (RE) were also heavily involved in the project, having produced and supplied PAPI units for the first trials that were conducted. The same design is still in use today.<ref>{{cite web |url=http://www.research-engineers.com/about_papi.html |title=Research Engineers PAPI |access-date=2017-05-14 |url-status=dead |archive-url=https://web.archive.org/web/20140125163859/http://research-engineers.com/about_papi.html |archive-date=2014-01-25 }}</ref>

Smith and Johnson's work was honoured by a commendation from the RAE, a Fellowship from the Aeronautical Society, an award from the American Flight Safety Foundation, and a Gold Medal from the British Guild of Air Pilots.{{cncitation needed|date=March 2023}}

PAPIs were used by NASA's Space Shuttle for its safe landing, for which Johnson was interviewed by UK local news media and TV.{{cncitation needed|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 }}).{{cncitation needed|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>

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* [[Optical landing system]]

* [[Leading lights]]

* [[Instrument landing system ]] (ILS)

==References==