ICAO PAPI Requirements & Compliance Guide
Siting, elevation, spacing, aiming, approach slope, threshold crossing height, minimum eye height, photometry, inspection and maintenance, and how ICAO and FAA values differ. Compliance is a connected engineering chain, so the guide explains why each parameter matters, which document governs it, and how to evidence it.
ICAO PAPI Overview
A Precision Approach Path Indicator (PAPI) gives pilots visual approach-slope guidance on final approach. Its performance depends on correct siting, installation, elevation, unit spacing, aiming, optical performance, colour, intensity, inspection and maintenance.
For international projects, assess PAPI requirements against the applicable edition of ICAO Annex 14, Volume I, the relevant ICAO guidance material and the requirements of the State or national aviation authority.
| Aircraft position | 4-unit PAPI |
|---|---|
| Too high | 4 White |
| Slightly high | 3 White + 1 Red |
| On approach path | 2 White + 2 Red |
| Slightly low | 1 White + 3 Red |
| Too low | 4 Red |
How red and white lights tell a pilot above, on or below the slope.
AGL Visual Encyclopedia: PAPI Optical Principle PAPI Glide Path PAPI System Overview
Which Document Governs a PAPI Value?
Choosing which standard governs a value.
AGL Visual Encyclopedia: Standard-Selection Flowchart Applicable-Standard Identification Standard Comparison
System Configuration and Unit Identification
Standard installation
Four light units in a row generally perpendicular to the runway centreline, with optical systems, light sources, mounting, electrical supply, control equipment, cabling, foundations and alignment and aiming provisions.
Different aiming per unit
Each unit has its own vertical aiming relationship to the others. The difference in aiming angles creates the red/white transition.
Consistent identification
The unit nearest the runway is the inboard unit and the furthest is the outboard unit. Label units A to D (or the project equivalent) consistently across drawings, test sheets and maintenance records.
How the PAPI units sit relative to the runway.
AGL Visual Encyclopedia: PAPI Unit Arrangement PAPI System Overview Different PAPI Systems
PAPI Location, Distance from Threshold and Elevation
PAPI location is not a convenient distance from the threshold. ICAO-related aerodrome inspection guidance describes it as determined from the approach angle, the difference in level between the threshold and the PAPI units, and the minimum eye height over the threshold. There is no single universal ICAO PAPI distance for every runway.
Calculation should consider
Selected approach slope, PAPI elevation, runway threshold elevation, required minimum eye height, aircraft characteristics, obstacle clearance and runway operational constraints. A change in PAPI elevation can change the nominal location.
Runway profile
Where runway elevation changes significantly between threshold and PAPI, the simple theoretical geometry may not hold. Use threshold elevation, unit elevation, centreline profile, terrain, runway slope and approach geometry from the actual survey.
Elevation survey
Establish survey references for the threshold, runway centreline, PAPI foundation, each unit and relevant reference points, and retain the results with the commissioning documents as the baseline for maintenance. An incorrect elevation affects approach slope, TCH, minimum eye height, location and visual indications.
Where the glide path meets the runway and how the PAPI sits to it.
AGL Visual Encyclopedia: PAPI Glide Path ILS Glide Slope ILS Siting and AGL Interface
Approach Slope, Setting Angles, TCH and Minimum Eye Height
| Concept | What it is | Note |
|---|---|---|
| Nominal approach slope | Intended vertical approach path for the PAPI | A design parameter, coordinated with approach design and other guidance such as ILS |
| Unit setting angle | Vertical aiming angle of an individual unit | Different per unit; values come from the current ICAO requirement or approved calculation |
| On-slope indication | 2 White + 2 Red on a four-unit PAPI | Defined by the unit setting angles |
| Transition boundaries | Upper and lower limits between indications | Set by the angular relationship between units |
| Threshold Crossing Height (TCH) | Height associated with the visual approach geometry at the threshold | Depends on approach angle, PAPI elevation and distance, eye-to-wheel geometry, minimum eye height, threshold elevation |
| Minimum Eye Height over Threshold (MEHT) | Operational characteristic of the indication, related to the setting angle of the unit defining the lower boundary of on-slope | Siting cannot be separated from aircraft approach geometry |
Aircraft characteristics
Consider cockpit height, eye-to-wheel height, aircraft category, approach speed and operational requirements. The most demanding aircraft expected to use the runway may drive the design; a design for one category is not automatically suitable for all.
Obstacles and ILS
PAPI does not remove the need for obstacle assessment. Where both PAPI and ILS exist, coordinate glide path, nominal slope, threshold crossing geometry, antenna location and eye height. Do not adjust a PAPI because it looks different from the ILS without checking the approved design relationship.
Elevation setting angles of the four units.
AGL Visual Encyclopedia: PAPI Elevation Angle PAPI Glide Path PAPI Optical Principle
Unit Spacing, Horizontal Alignment and Aiming
Spacing
Establish spacing from the applicable design requirements and drawings, then measure and record the actual value instead of judging by eye.
Horizontal alignment
Alignment controls beam azimuth. Vertical angles can be perfect and the guidance still wrong if the units are horizontally misaligned. Check with a survey or alignment method and record runway reference, azimuth, design, actual, tolerance and result.
Spacing record
| Measurement | Design | Actual | Difference | Status |
|---|---|---|---|---|
| Unit A–B | Approved value | Measured | Calculated | Pass/Fail |
| Unit B–C | Approved value | Measured | Calculated | Pass/Fail |
| Unit C–D | Approved value | Measured | Calculated | Pass/Fail |
Aiming: the four units are not aimed at identical vertical angles. The setting angles create the 4 White, 3W/1R, 2W/2R, 1W/3R and 4 Red sectors. The exact angles and tolerances come from the current ICAO requirements and the approved project design.
Related Guides
Elevation adjustment Azimuth adjustment PAPI Alignment, Testing & Maintenance Field GuideHorizontal alignment of the units to the runway.
AGL Visual Encyclopedia: PAPI Azimuth Alignment PAPI Alignment PAPI Unit Arrangement
Which Standard Should You Cite?
Pick the governing basis and the parameter to see how to reference it without mixing ICAO and FAA numbers.
PAPI Photometry, Intensity, Colour and Beam Coverage
Photometry verifies optical performance. Depending on the applicable standard and procedure it can address intensity, beam distribution, colour, red/white transition, horizontal and vertical coverage and individual unit performance, using calibrated equipment and an approved procedure. A simple visual check cannot establish photometric compliance.
Intensity
Affected by light-source condition, contamination, filter, optical alignment, electrical supply, internal optics and environment. Produce measured data per unit.
Colour
Relies on distinguishing aviation white and aviation red. Abnormal colour can come from damaged filters, contamination, wrong components, source degradation or internal damage.
Transition and coverage
The transition must be defined enough to give the intended information. A unit can have adequate centre-beam intensity and still fail elsewhere in its distribution. Do not judge colour by looking at the unit from close range.
Equipment
Calibrated photometer, angular measurement system, alignment equipment, colour measurement equipment, data acquisition and reference equipment. Before testing check identification, calibration status, range, resolution, test configuration and environment.
Test report should identify
Instrument manufacturer, model, serial number, calibration date and certificate, measurement range, test date, technician and environmental conditions, so an auditor can see how the result was obtained.
The PAPI beam, its sectors and its coverage.
AGL Visual Encyclopedia: PAPI Beam Beam Intensity Photometric Compliance Flow
PAPI Inspection and Maintenance
Inspection
Visual: output, housing, lens, contamination, damage, obstructions, foundation, mounting. Mechanical: level, alignment, mounting, fasteners, foundation. Electrical: supply, wiring, connectors, protection, controls. Photometric: applicable intensity, colour, distribution, transition.
Maintenance activities
Cleaning, visual, optical, mechanical and electrical inspection, alignment verification, functional testing, photometry where required, fault recording and corrective maintenance.
| Trigger | Reassess |
|---|---|
| Impact (vehicle, mower, snowplough), construction, foundation work, severe weather, suspected movement | Position → level → alignment → aiming → optics → electrical → photometry. A unit that still lights may no longer be aligned |
| Runway rehabilitation or resurfacing | Runway, PAPI and threshold elevation relationship and approach geometry, before returning the runway to normal operation |
What an inspection of a PAPI unit covers.
AGL Visual Encyclopedia: PAPI Inspection PAPI Testing PAPI Troubleshooting
PAPI vs APAPI and ICAO vs FAA
| Feature | PAPI | APAPI |
|---|---|---|
| Light units | 4 | 2 |
| Visual indication | Four-unit sequence | Two-unit sequence |
| Installation | Standard configuration | Abbreviated configuration |
| Siting | Project-specific | Project-specific |
| Aiming | Multiple setting angles | Different two-unit geometry |
Shared concepts
PAPI gives visual approach guidance; the four-unit PAPI uses different aiming angles; siting, elevation, TCH/MEHT, optical performance, inspection and maintenance all matter.
Where they differ
Numerical requirements, terminology, tolerances, siting procedures and equipment specifications. Use FAA publications for FAA-governed projects, and ICAO provisions plus the State's implementation for ICAO-based projects.
Misleading
"According to ICAO, PAPI units should be spaced at X metres," when X came from an FAA advisory circular.
Better
"The applicable PAPI spacing shall be established in accordance with the current ICAO/State requirements and approved project design." Cite the specific controlled provision if a number is needed.
Four-unit PAPI against two-unit APAPI.
AGL Visual Encyclopedia: PAPI versus APAPI APAPI Configuration VASI versus PAPI
Commissioning Procedure and Maintenance Workflow
Review approved design
Confirm applicable ICAO and State requirements
Verify PAPI location
Verify elevation
Verify unit spacing
Level units
Check horizontal alignment
Set individual aiming angles
Complete electrical checks
Perform functional test
Perform photometric testing
Correct deficiencies and repeat measurements
Compile commissioning report
Obtain operational acceptance
Maintenance and corrective-action loop
Steps in commissioning a PAPI.
AGL Visual Encyclopedia: PAPI Commissioning PAPI Installation PAPI Testing
As-Built Documentation, Baselines and Audit File
As-built and baseline
Record coordinates, elevations, spacing, runway offset, aiming angles, equipment model and serial numbers, electrical and control arrangement and photometric results. Baseline data (unit elevation, alignment, aiming angle, intensity, colour, beam, electrical measurements) lets future maintenance compare with the accepted condition. The original design drawing is not enough.
Audit file
Approved design, siting calculation, survey data, installation and as-built drawings, alignment records, photometric reports, calibration certificates, commissioning report, maintenance, fault and corrective-action records, and equipment manuals.
Typical deficiencies to assess against the applicable requirement.
What the audit file has to show.
AGL Visual Encyclopedia: Compliance Matrix Compliance Decision Tree
ICAO PAPI Compliance Checklist
Click an item to mark it complete.
Design
Installation
Electrical and Optical
Documentation
Deciding whether an installation complies.
AGL Visual Encyclopedia: Compliance Decision Tree Compliance Matrix Regulator Comparison Matrix (ICAO, EASA, FAA, DGCA)
Operations, Certification and What Engineers Should Verify
PAPI is an operational visual aid, so compliance must support reliability: availability, correct indication, brightness, alignment, maintenance status, fault reporting and aerodrome operating procedures. ICAO contingency material lists visual-aid status, including PAPI calibration, among items for assessing aerodrome readiness, and Annex 14 Vol. I is a core reference for aerodrome certification.
Location
Is the PAPI correctly sited?
Elevation
Is the installed elevation correct?
Spacing
Are the units correctly positioned?
Alignment
Aligned with the runway?
Aiming
Are setting angles correct?
Geometry
Does it give the required approach path and threshold crossing geometry?
Optics
Intensity and colour acceptable?
Electrical
Reliably powered and controlled?
Maintenance
Is performance being maintained?
Documentation
Can every key parameter be shown in records?
Quick Knowledge Check
Q1. Does ICAO specify one universal PAPI distance from the threshold?
Q2. An FAA spacing figure is found online. How should it appear in an ICAO-based compliance table?
Q3. Which statement about unit setting angles is correct?
Q4. What should be done after a vehicle strikes a PAPI unit that still lights?
Q5. Where should the PAPI inspection interval come from?
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Aiming records, checks and maintenance.
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From the governing standard to the as-built record, explore the complete AGL knowledge base for PAPI compliance.
Explore the AGL Engineering Knowledge Hub
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Runway, Taxiway & Approach Lighting
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ICAO PAPI Requirements FAQ
Q1What is the ICAO standard for PAPI?
PAPI requirements are primarily in ICAO Annex 14, Volume I (Aerodromes: Design and Operations), together with relevant ICAO guidance and applicable State requirements.
Q2Does ICAO specify PAPI installation requirements?
Yes. ICAO aerodrome provisions address the design and operational requirements for visual aids including PAPI. Check the current applicable edition and the State implementation.
Q3How many lights does an ICAO PAPI have?
A standard PAPI uses four light units. APAPI is the two-unit abbreviated configuration.
Q4What is the PAPI approach angle?
The nominal approach slope comes from the approved aerodrome design. Individual units have different setting angles that create the visual indications.
Q5Does ICAO specify one universal PAPI distance from the threshold?
No. Location comes from the geometry, including approach slope, PAPI elevation, threshold elevation and minimum eye height considerations.
Q6What is PAPI TCH?
Threshold Crossing Height: the height associated with the aircraft's visual approach geometry at the threshold, considered when determining PAPI location and approach-slope geometry.
Q7Does PAPI require photometric testing?
Optical performance should be verified according to the applicable equipment, inspection and regulatory requirements. Photometry gives objective evidence of intensity, colour and beam performance.
Q8What is the difference between PAPI and APAPI?
PAPI normally uses four units and APAPI uses two, so the visual indication and design geometry differ.
Q9Are ICAO and FAA PAPI requirements the same?
No. The principles are similar, but numerical requirements, terminology, tolerances and procedures can differ. Use the governing standard for the project.
Q10Can FAA PAPI values be used for an ICAO project?
Only where the project or competent authority specifically adopts them. Do not present FAA values as ICAO requirements without verification.
Q11What documents should be checked before PAPI installation?
The applicable ICAO provisions, State or national authority requirements, approved aerodrome design, PAPI equipment documentation and project specifications.
Q12How often should PAPI be inspected?
The interval comes from the airport maintenance programme, authority requirements and equipment documentation. Do not use an arbitrary generic interval as a regulatory requirement.
Q13What should be done after PAPI maintenance?
Verify the work, check the physical installation, confirm alignment where affected, run a functional test, perform photometry where required, and record the results.
Engineering & Expert Notes
Identify Which Document Governs Each Value
Governing TextCheck the source for each parameter and avoid mixing figures from different frameworks.
Siting and Setting Angles Must Be Consistent
GeometryVerify that the design basis, survey data and installation match.
Check Alignment Method and Equipment
AlignmentRecord the method, instrument and calibration so results can be trusted.
Verify Photometry and Colour
PhotometryMeasured values support compliance statements better than assumptions.
Plan Periodic Re-Verification
MaintenanceSet re-check intervals, including after impacts and changes to the surrounding area.
Keep a Compliance Dossier
RecordsHold the design basis, as-built data and test results together for audits.
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