Precision approach path indicator: Difference between revisions

Revision as of 10:17, 30 August 2008

Revision as of 10:48, 24 September 2008

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The PAPI is usually located on the left side of the runway and can be seen up to five miles during the day and twenty miles at night. It has two or four lights installed in a single row instead of far and near bars that would be characteristic of Visual Approach Slope Indicator (VASI).

Each box of lights is equipped with an optical apparatus that splits light output into two segments, red and white. Depending on the angle of approach, the lights will appear either red or white to the [[aviator|pilot]]. Ideally the total of lights will change from white to half red, moving in succession from rightleft to leftright side. The pilot will have reached the normal glidepath (usually 3 degrees) when there is an even split in red and white lights. If an aircraft is beneath the glidepath, red lights will outnumber white; if an aircraft is above the glidepath, more white lights are visible.

During aircraft [[descent (aircraft)|descent]], this system, 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]].