PAPI Sytems
This system uses light units installed in a single row of either two or four light units. Lights are visible from about 5 miles during the day and up to 20 miles at night. The visual glide path of the PAPI provides in most cases safe obstruction clearance within plus or minus 10 degrees of the extended runway centerline and to 4 SM from the runway threshold.
Descent, using the PAPI, should not be initiated until the aircraft is visually aligned with the runway.
PAPI’s are usually situated around 1000’ from the threshold of the runway. Regardless of the placement of the PAPIs it will always provide obstruction clearance. This also happens to be in the general vicinity of the visual aim point and the ILS/GS installation, give or take a few feet. If there is an alignment issue between the ILS/GS or Non‐ILS descent angle and the PAPI glidepath you will see the following note: “VGSI and descent angles not coincident” or “VGSI and ILS glidepath not coincident on an approach plate”.
Facts to Know:
The visual glidepath will be at least 1 degree above all obstacles in the final approach area. The VGSI must provide clearance above all obstacles within the commissioned operational service volume.
Flight inspection does verify that specific VGSI below path indications clear all obstacles within the commissioned operational service volume.
When VGSI and electronic glide path information serve the same runway, the visual approach path will coincide with the one produced electronically
The default PAPI glidepath angle is 3 degrees.
The PAPI glidepath for the typical Air Carrier airport with a TCH of 50 ft, will produce a touchdown point at 954 feet from the threshold regardless of runway length, assuming no flare maneuver is used.
