What is PAPI installation?
Putting a PAPI wing bar into service as one system — four units set out in one line, mounted level on frangible couplings, connected to the series cable and earth, aimed at their own angles and proved before the aid is released.
PAPI installation is erecting the four units of a wing bar so that they work as one slope indicator: set out in one straight line beside the runway, in the designed order, mounted level on frangible couplings over their foundations, connected through the series cable and isolating transformers, earthed, then aimed and proved before the aid is released.
A PAPI fails quietly. Adjacent units are set only about 20 arcminutes apart, so a unit that is swapped, twisted or tilted gives the pilot a wrong slope cue that cannot be seen from the ground. Work from the design drawings and the as-built foundation record, keep each unit’s place and identity, leave the aiming until the unit is mounted and connected, and read the angles again after the fasteners are tightened. See PAPI Alignment for re-setting, PAPI Testing and PAPI Commissioning for the proof. Treat the circuit as live until it has been isolated, locked out and proved dead.
- Isolate. Isolate the circuit, lock it out, prove it dead, and hold the permit-to-work and runway-operations permission.
- Check the bases. Confirm each footing is cured, level and in line, the bolts are clean and the as-built position is on record.
- Mount the units. Fit each unit in its designed place on its frangible coupling, at the design height, level, with fasteners to the specified torque.
- Connect. Make the cable, transformer and earth connections as designed, keep the unit order, then seal every entry and connector.
- Aim. Set each unit’s elevation to its own setting angle and its azimuth parallel to the runway centreline, then read both again.
- Test and record. Prove insulation and continuity, light the units, check a sharp white-to-red change at each setting, record the readings and clear all tools.
Frequently Asked Questions
Q1What is PAPI installation in AGL construction?
Erecting the four units of a PAPI wing bar so that they work together as one slope indicator. It covers checking the foundations, mounting each unit in its place on a frangible coupling, making the cable, transformer and earth connections, aiming each unit at its own angle, and proving the result before the aid is released for use.
Q2Why must the four units be in one line and in the right order?
The pilot reads all four units together, and each unit is set at its own angle, only about 20 arcminutes from its neighbour. The units must therefore stand in the designed order, in one straight line at the design spacing and offset from the runway edge. A unit that is swapped, out of line or tilted gives a wrong slope cue that the pilot cannot detect.
Q3How is a PAPI unit mounted so that it stays frangible?
Fit it on the manufacturer’s frangible coupling at the design height, with the break point where the design puts it. Do not add bracing, grout or fixings that bridge the break point, and leave the cable with enough slack that it does not hold the unit up. Tighten the fasteners to the specified torque and keep the unit level.
Q4Is aiming part of installation?
Yes, and it is the last step before testing. Each unit is set to its own setting angle in elevation, read with an inclinometer on its reference surface, and aimed parallel to the runway centreline in azimuth. Read both again after tightening, because tightening can move the unit. The final proof is a flight inspection, as the authority requires.
Q5What is checked before a new PAPI is released for use?
Check that the units are in order and identified, level, and fixed to the specified torque, and that the connections are sealed. Prove insulation and continuity, then light the units and check that each shows a sharp white-to-red change at its setting. Record the as-built readings, and complete the airport’s commissioning and flight-inspection steps before the aid is released.
See It. Understand It. Then Learn How to Engineer It.
Recognising an AGL system visually is the first step. The next step is knowing how to design, install, test, commission and maintain them correctly.
Build Practical AGL Engineering Skills
Go deeper with structured training from Precision AGL Academy, covering:
Learn how each light, sign and circuit works as part of a complete airport lighting system, not just as an isolated diagram.