Controlled procedures for Precision Approach Path Indicator (PAPI) and, where still installed, legacy Visual Approach Slope Indicator (VASI) units — positioning, azimuth and elevation alignment, aiming-angle setting, optical adjustment, lamp/LED module replacement, electrical connection and power supply verification, heater operation, functional testing, photometric testing and periodic inspection.
Scope Note — The procedures in this division are written around PAPI (and APAPI where applicable), the current ICAO Annex 14 standard visual approach slope system. Legacy VASI / T-VASIS installations follow the same control principles — position, elevation, aiming angle, transition sector, electrical isolation, functional and photometric verification, and flight inspection — but shall use the site-specific values and adjustment procedures of the approved design and manufacturer documentation. Do not apply PAPI unit counts, spacing or angle logic to VASI bars.
Technical Control — PAPI is a precision visual approach-slope system. Exact PAPI location, elevation, azimuth, approach-slope angle, unit separation, aiming angles, photometric requirements, power supply and acceptance criteria shall be taken from the approved aerodrome design, applicable ICAO Annex 14 / national requirements, DGCA requirements where applicable, approved survey data, manufacturer documentation and project specification. Do not use generic values where approved site-specific values exist.
To establish a controlled procedure for installing PAPI units at the approved location, elevation and orientation.
Verify:
PAPI shall be accepted only when Location + Elevation + Azimuth + Aiming Angles + Unit Spacing + Optical Performance + Electrical Operation are verified, and flight inspection is satisfactorily completed where required.
Critical Principle — PAPI positioning and PAPI alignment are separate controls. A perfectly aligned unit installed at the wrong location can still provide an incorrect approach indication.
To ensure each PAPI unit is positioned at its approved longitudinal, lateral and vertical location.
Positioning shall be based on:
To establish the complete alignment procedure for PAPI units.
Verify:
Important — Azimuth alignment shall not be based solely on visual judgment from the runway.
To ensure PAPI units are correctly oriented in the horizontal plane toward the intended approach path.
Critical Check — Any unexplained elevation difference between units shall be investigated before final optical alignment.
To ensure each PAPI unit has the correct elevation relative to the runway and approved PAPI reference.
Important — Do not insert generic PAPI aiming-angle values into the SOP. The approved project/site-specific values shall control.
To establish the approved vertical aiming angles for each PAPI unit.
Critical Rule — Only approved adjustment procedures and manufacturer-specified tools shall be used.
To ensure the PAPI optical system provides the intended transition between visual indications.
Check:
Critical Rule — Replacement lamp type, rating and optical characteristics must match the approved PAPI configuration.
To establish a controlled procedure for replacing conventional PAPI lamps where applicable.
To ensure defective PAPI LED modules are replaced without changing the approved optical characteristics.
To maintain optical performance and environmental integrity.
Clean/inspect:
To ensure reliable and safe electrical connection of PAPI units.
To verify that the PAPI receives the required electrical supply.
Power supply must comply with the manufacturer's specified operating requirements and approved project design.
To verify correct operation of the PAPI heater/anti-condensation system where fitted.
Check for:
To verify complete PAPI operation after installation, adjustment or maintenance.
Confirm:
To verify the photometric performance of the PAPI system against applicable requirements.
Depending on the approved procedure, assess:
Record:
Critical Principle — A PAPI should be considered correctly aligned only after both survey/physical verification and optical verification have been satisfactorily completed.
To independently verify the final physical and optical alignment of the PAPI system after installation or maintenance.
Check:
To establish a systematic periodic inspection program for maintaining PAPI reliability and accuracy.
A. Physical
B. Optical
C. Alignment
D. Electrical
E. Environmental
Master installation workflow, quality hold points, master inspection checklist and common failure modes that apply across all 17 Division 11 procedures.
The following sequence should be applied whenever applicable:
Work shall not proceed past a hold point until the associated inspection or verification has been completed and released.
The installation/inspection team should specifically monitor:
The following conditions should be specifically monitored during AGL maintenance:
The AGL installation/maintenance organization should maintain, as applicable:
"PAPI is not simply a row of four lights. It is a calibrated visual approach-slope guidance system in which position, elevation, azimuth, individual aiming angles, optical performance and unit-to-unit relationship must work together. Any change in the physical installation or optical system can affect the guidance indication and therefore requires controlled verification."
Final PAPI location, elevation, azimuth, approach-slope angle, unit separation, aiming angles, photometric requirements and power supply arrangements shall be based on the approved aerodrome design, applicable ICAO Annex 14 / national requirements, DGCA requirements where applicable, approved survey data and manufacturer documentation.
Approved site-specific design values and manufacturer documentation shall take precedence wherever they impose more restrictive requirements than a generic value.
Technical references behind the procedures in this division:
References are given at document or chapter level for technical orientation. Confirm the current edition, amendments and national adoption (for example DGCA CAR Section 4, FAA Advisory Circulars or EASA material) for each project. Approved project specifications, manufacturer instructions and the airport's own procedures take precedence, as stated in the precedence note above.
Quick answers about PAPI / VASI SOPs in the AGL SOP Library.
Division 11 is a set of 17 procedures (SOP-219 to SOP-235, Rev 0) for Precision Approach Path Indicator (PAPI) units and, where still installed, legacy VASI units. It covers positioning, azimuth and elevation alignment, aiming-angle setting, optical adjustment, lamp and LED module replacement, electrical connection and power supply verification, heater operation, functional and photometric testing, and periodic inspection.
From the approved aerodrome design, applicable ICAO Annex 14 and national or DGCA requirements, approved survey data, manufacturer documentation and the project specification. Generic values must not be used where approved site-specific values apply, and generic aiming-angle values must not be inserted into the SOP (SOP-224).
Confirm the approved angle settings, verify calibration of the alignment equipment, establish a reference plane, set the specified angle for each unit and verify each unit independently. Confirm the correct sequence across the system, lock the adjustment mechanisms and record final settings (SOP-224).
Any unexplained elevation difference between units must be investigated before final optical alignment (SOP-223). Verify approved elevation data, establish a survey datum, measure each unit, verify the unit-to-unit relationship and check for foundation settlement.
Depending on the approved procedure: light intensity, beam distribution, horizontal and vertical coverage, transition characteristics, colour, intensity settings, individual unit performance and system consistency. It uses calibrated test equipment after confirming PAPI alignment (SOP-233).
Where fitted, SOP-231 verifies the heater specification, connections and control circuit, energizes the heater per the approved procedure and checks for abnormal heating, thermostat function, condensation, moisture, damaged wiring and control malfunction.
Knowing the alignment procedure is essential. Understanding how PAPI angular settings, siting and electrical supply affect approach slope guidance takes deeper technical knowledge.
Learn through structured training covering:
Develop the technical foundation to work with AGL systems systematically, safely and confidently.
Please read before relying on any content on this page or on any SOP downloaded from it.