What are PAPI foundations?
The concrete footings under each PAPI unit. They must stay firm, level and in line for the life of the installation, because the unit’s signal is an angle.
A PAPI foundation is the concrete footing under a PAPI unit, normally one for each unit. It carries the anchor bolts or mounting plate, a duct stub-up for the cable and an earth connection, with the unit above it on a frangible coupling and the foundation top kept low and level.
It is a civil interface because the civil works excavate, compact, drain and pour it, while the AGL design sets its position, line and offset from the runway edge, bolt layout, duct, earth and top level. It matters more than most light foundations because a PAPI signal is an angle: adjacent units are set only about 20 arcminutes apart, so a footing that settles, heaves or keeps moving shifts where each unit changes from white to red. The unit’s own levelling adjustment can absorb a small error at commissioning, but not ground that moves afterwards.
Carries an optical unit whose angle is the signal, so the base must stay firm, level and in line for life.
Carries an elevated light on a frangible coupling, where a small tilt rarely changes what the pilot sees.
Frequently Asked Questions
Q1What are PAPI foundations?
PAPI foundations are the concrete footings under the units of a PAPI wing bar, normally one per unit. Each carries the anchor bolts or mounting plate, a duct stub-up for the cable and an earth connection, and holds its unit at the surveyed position with a low, level top. The civil works build them to the AGL design.
Q2Why are PAPI foundations held to tighter movement limits than other light foundations?
A PAPI signal is an angle. Adjacent units are set only about 20 arcminutes apart in elevation, so a footing that settles, heaves or keeps moving shifts where a unit changes from white to red, and the pilot cannot see why. An elevated edge light can tolerate more movement because it gives no angular cue.
Q3What does the civil team provide and what does the AGL design set?
The civil works provide excavation, a firm compacted base, drainage, formwork and the concrete. The AGL design sets the position, the line and offset from the runway edge, the bolt layout from the manufacturer’s template, the duct and earth provision, and the level the top must meet.
Q4Why do soil and frost conditions matter?
Soft, loose or wet ground lets a footing settle, and frost can lift it. Either one tilts the unit slowly after commissioning. The geotechnical advice sets the depth and size of the footing so the base stays firm and drained for the life of the installation.
Q5Why is the foundation top kept low and the unit frangible?
A PAPI stands close to the runway, so an aircraft that strays onto it must not meet a solid obstacle. The foundation top is kept low, and the unit is mounted on a frangible coupling above it so it breaks away cleanly while the footing stays in the ground.
Q6What should be signed off before the unit is mounted?
The footing is in the surveyed position and in line with the others, the top and bolt pattern are level and true to the drawing tolerance, the duct and earth are in place, the concrete has cured without cracks or voids, and the as-built position and level are recorded. Cable locations are checked and the permit issued before any excavation.
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