Installing or Upgrading PAPI: What Airports Need to Get Right
A PAPI installation can seem straightforward: install the units, aim them to the correct angle, connect the power and commission the system.
In practice, a PAPI project needs careful design. Whether the airport is replacing T-VASIS, installing PAPI for the first time, relocating an existing PAPI, or changing the system to suit a revised design aircraft, the key issues are the same: siting, obstacle protection, aircraft eye height, civil works, electrical infrastructure and commissioning.
Getting any of these wrong can create problems late in the project, when they are most expensive to fix.
PAPI siting is the critical design step
The heart of a PAPI design is the relationship between three things:
- the approach slope the PAPI is intended to indicate;
- the eye height over threshold required for the aircraft using the runway; and
- the obstacle environment below the approach path.
These items are linked. Moving the PAPI further from the threshold changes the eye height outcome and the obstacle assessment. Adjusting the approach slope can affect instrument procedure compatibility, obstacle clearance and pilot expectations.
This is why PAPI siting should be based on current survey data, confirmed runway geometry and a proper obstacle assessment. It should not be treated as a simple field placement exercise.
Different project types create different risks
A PAPI project may be triggered for several reasons.
If replacing T-VASIS, the new PAPI will usually need its own siting calculation, civil works and electrical arrangement. It should not be assumed that the PAPI can simply be installed in the old T-VASIS footprint.
If installing PAPI where no visual approach slope system currently exists, the project needs to confirm the appropriate runway end, approach slope, aircraft design assumptions, obstacle environment and operational need.
If relocating an existing PAPI, the design needs to check whether the new location still provides the required eye height over threshold and obstacle protection.
If upgrading the system for a new or larger design aircraft, the siting may need to change to suit the revised eye height requirement. This can have flow-on effects for cable routes, grading, circuit capacity and commissioning.
Common items that get underestimated
Civil works
PAPI units need stable mounting, correct levels and suitable grading around the installation. Small level changes can affect beam alignment, so the local ground profile matters.
Electrical infrastructure
A PAPI may require new pits, ducts, cabling, isolating transformers and circuit capacity. On some projects, the electrical infrastructure costs more than the PAPI units themselves.
Control and monitoring
The PAPI needs to operate consistently with the rest of the airfield lighting. Switching, intensity control, monitoring and fault reporting should be considered early, especially where the airport has an existing AGL control system.
Frangibility and mounting
The units, supports and secondary cable retention need to be suitable for the runway strip environment. Mounting heights, frangible supports, local grading and cable restraint should be resolved together, not separately.
Redundant infrastructure
Where an existing system is being replaced or relocated, the removal or isolation of old fittings, pits, transformers and cabling should be clearly defined. Leaving redundant infrastructure behind creates confusion for future maintenance and upgrade works.
Commissioning is not a formality
PAPI commissioning should be planned into the project from the start.
Ground commissioning needs to verify the installation, aiming angles, light characteristics, electrical performance, switching, intensity control and monitoring. Flight checking confirms that the visual indications are correct from the pilot’s perspective.
Commissioning also needs to be coordinated with operational changes, documentation updates and NOTAM requirements. CASA guidance requires aerodrome lighting systems to be commissioned before being made available for use, and the commissioning process produces the evidence needed before NOTAM or AIP/ERSA updates.
Live operations need a transition plan
Most PAPI projects happen at operating aerodromes.
The project needs to consider how the works area will be managed airside, whether runway closures are required, what guidance is available to pilots during the transition, and how commissioning will be sequenced.
These questions should be answered during design, not after construction has started.
The takeaway
A PAPI project is not just an equipment installation. It is a design exercise that links aircraft operations, obstacle protection, civil levels, electrical infrastructure and commissioning.
The projects that run smoothly are the ones that confirm the siting, survey, obstacle assessment and operational requirements early.
Whether the airport is replacing T-VASIS, installing PAPI for the first time, relocating an existing system or upgrading for a different aircraft type, the same principle applies: answer the design questions before the works are priced and built.