Precision approach path indicator: Difference between revisions

Revision as of 14:52, 1 March 2023

Revision as of 14:56, 1 March 2023

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[[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.]]

==HistoryDesign==

A typical engineering design specification for a PAPI light unit is shown below:

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>

[[File:PAPI-Section.svg|thumb|350px|Schematic diagram of longitudinal section<br />

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

Optical construction:

* Preadjusted 2-lamp optical assembly.

* Anodized aluminium reflectors.

* Red color filters.

* Precision-ground lenses.

* Lamps and reflectors replaceable without recalibration.

* 2 x 200 W / 6,6 A prefocused halogen lamps, Pk30d base.

* Average lifetime 1000 hours at rated current.

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>

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.{{cn}}

==Interpretation==

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}}

==Meaning==

[[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. For the optimum approach angle the ratio of white to red lights will remain 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}}

==Background==

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.

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PAPI systems are readily available from airfield lighting manufacturers worldwide. PAPI is normally operated by [[air traffic control]] (ATC). If ATC services are not normally provided at an aerodrome, PAPI along with other airport lights may be [[pilot-controlled lighting|activated by the pilot]] by keying the aircraft microphone with the aircraft's communication radio tuned to the [[CTAF]] or dedicated pilot controlled lighting (PCL) frequency.

==DesignHistory==

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>

A typical engineering design specification for a PAPI light unit is shown below:

[[File:PAPI-Section.svg|thumb|350px|Schematic diagram of longitudinal section<br />

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

Optical construction:

* Preadjusted 2-lamp optical assembly.

* Anodized aluminium reflectors.

* Red color filters.

* Precision-ground lenses.

* Lamps and reflectors replaceable without recalibration.

* 2 x 200 W / 6,6 A prefocused halogen lamps, Pk30d base.

* Average lifetime 1000 hours at rated current.

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.{{cn}}

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>

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}}

The PAPI system is co-opted for use by the [[final approach (aviation)|Final Approach]] Runway Occupancy Signal (FAROS) system being introduced<ref>{{Cite web|url=http://www.faraim.org/aim/aim-4-03-14-87.html|title=Aeronautical Information Manual (AIM) - Page 87|website=www.faraim.org|access-date=2019-12-24}}</ref> by several major airports in the United States for the purpose of allowing pilots to resolve a [[runway incursion]] without requiring ''a priori'' notice of an occupied runway from the [[control tower]]. In FAROS, automated line-of-sight runway sensors detect if a vehicle has committed a runway incursion, and if so, will flash the PAPI lights to alert the pilot of an aircraft on final approach that the runway is currently occupied. The pilot then becomes responsible for resolving the conflict by notifying the [[air traffic controller]] and executing a [[go-around]]. Once the tower has ascertained that the runway has been cleared, the ground controller resets the PAPI so that landing operations may resume normally.<ref>{{cite web |url=https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/operations/td/projects/faros/solution/animation.cfm |title=Final Approach Runway Occupancy Signal (FAROS) - Animation |access-date=2010-06-07 |url-status=dead |archive-url=https://web.archive.org/web/20100209024258/https://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/operations/td/projects/faros/solution/animation.cfm |archive-date=2010-02-09 }}</ref><ref>{{cite web |url=https://www.faa.gov/air_traffic/publications/atpubs/aim_html/chap2_section_1.html |title=Section 1. Airport Lighting Aids |access-date=2019-09-19 }}</ref>