Visual Approach Slope
PAPI System (2-Unit / 4-Unit)
Precision Approach Path Indicator systems with installation, alignment and verification support
PAPI gives pilots immediate visual indication of whether they are above, on, or below the approach path. Precision AGL Solutions supports projects from configuration review through installation, alignment and final performance verification.
Supplied by Precision AGL Solutions
Visual Approach Slope Indication
PAPI System (2-Unit / 4-Unit)
What PAPI Does
Precision AGL Solutions provides Precision Approach Path Indicator (PAPI) systems for runway approaches requiring visual vertical guidance. PAPI presents a combination of red and white indications that changes with the aircraft's position relative to the approach slope, showing whether the pilot is above, on, or below the intended path.
FAA guidance describes PAPI as a row of two or four focused light units, normally installed on the left side of the runway. ICAO Annex 14 likewise places the wing bar on the left side unless that is physically impracticable.
More Than the Light Units
Performance depends on runway reference data, siting, elevation, approach angle, unit spacing, azimuth alignment, aircraft eye-to-wheel characteristics, threshold crossing height, obstruction clearance and verification procedures.
We therefore support PAPI projects from configuration review through installation, alignment and final performance verification.
Important Configuration Terminology
Specify by Number of Light Units, Not “Bars”
| FAA designation | Configuration | Description |
|---|---|---|
| L-880 | 4 light units | Standard four-unit PAPI arrangement |
| L-881 | 2 light units | Two-unit PAPI arrangement |
The term 3-bar is more commonly used for three-bar VASI systems. FAA aeronautical information distinguishes two- and three-bar VASI from PAPI, which uses two or four light units. Where a brief says “2-bar / 3-bar PAPI”, confirm the intended arrangement against the national aerodrome standard, project specification and authority-approved configuration before equipment selection.
Overview of Indications
Red / White Optical Sectors
A PAPI is a runway-side visual aid giving vertical slope information through sharply defined red/white sectors. The pilot interprets the relative number of red and white indications to judge position against the approach path.
| Aircraft position | Typical indication (four-unit) |
|---|---|
| Well above approach slope | All units white |
| Slightly above approach slope | Three white, one red |
| On or close to approach slope | Two white, two red |
| Slightly below approach slope | One white, three red |
| Well below approach slope | All units red |
Four-Unit PAPI — Pilot's View
A two-unit PAPI (APAPI, FAA L-881) gives three sectors instead of five. On or close to the slope the unit nearer the runway shows red and the farther unit white; above the slope both show white; below it both show red. It must still be located and aimed to provide the required guidance for the approved runway application.
Primary Applications
Where PAPI Is Considered
Visual slope indicationRunways requiring visual approach slope guidance.
New runway constructionIncluded in new visual-aid packages.
Rehabilitation & upgradesRunway rehabilitation and lighting upgrades.
Modernising older systemsConversion of older visual glide-path systems.
Complementing instrument approachVisual guidance alongside instrument approach facilities.
ILS / GLS / LPV coordinationCoordinated visual and electronic glide paths.
Replacement programmesAgeing, misaligned or obsolete PAPI equipment.
PAPI siting is an aerodrome engineering task, not simply a fixture replacement exercise.
System Scope
Typical Package Elements
| System element | Function |
|---|---|
| PAPI light units | Produce the red/white directional signal sectors |
| Mounting assemblies | Maintain unit geometry, stability and installation elevation |
| Power supply equipment | Provides the required electrical operating arrangement |
| Isolation / circuit equipment | Where required by the electrical architecture |
| Cabling and connectors | Connection between light units and system supply |
| Adjustment hardware | Controlled vertical and azimuth aiming |
| Protection / environmental accessories | Operation in the airfield environment |
| Monitoring or control interface | Where required by the control philosophy |
| Reference / aiming equipment | Installation alignment and commissioning |
| Verification accessories | Inspection, angular checks and field adjustment |
The final bill of materials follows the approved system architecture, applicable standard, electrical design and site conditions.
PAPI Installation Engineering
Small Errors Change the Apparent Slope
Small errors in elevation, angular setting or physical position can alter the apparent approach slope and reduce the consistency of the visual indication.
Siting
The reference position comes from threshold geometry, desired slope, threshold crossing height and aircraft characteristics.
Where ILS, GLS or LPV exists, FAA AC 150/5340-30J places the PAPI runway reference point relative to the glide-path touchdown point, so the visual and electronic paths are coordinated. Without one, FAA describes a method using threshold crossing height and the angle of the lowest on-course signal to find the distance from the threshold.
The FAA equipment standard (AC 150/5345-28H) is written for light units spaced 20–30 ft (6–10 m) apart, and ICAO Annex 14 requires equal spacing. Confirm the exact spacing and the distance from the runway edge in the applicable standard. FAA Engineering Brief #95 covers additional siting and survey considerations.
Obstacle Protection Surface
ICAO Annex 14 requires an obstacle protection surface for a PAPI or APAPI. No object may penetrate it unless it is shielded by an existing object or the authority judges it will not adversely affect safety. Survey the approach for obstacles before the PAPI position and angle are fixed, and keep the check current during the life of the installation.
Approach Angle
The standard PAPI glideslope referenced by FAA guidance is 3°. For certain non-jet runways, FAA permits considering a higher angle for obstacle clearance, subject to design requirements.
Do not treat the angle as a generic product setting; establish it from the approved runway design and aircraft population.
ICAO Annex 14 also ties the setting to a minimum eye height over the threshold for the aircraft eye-to-wheel height group using the runway, so confirm the group and the resulting threshold crossing height before fixing the angle.
Transverse Alignment
- Common elevation reference and relative unit height
- Transverse slope and unit spacing
- Azimuth alignment
- Perpendicular relationship to runway centreline
- Stability of each mounting point
- Correct unit identification and sequence
- Freedom from obstruction by pavement, vegetation, equipment or structures
ICAO-aligned guidance stresses a consistent horizontal plane and an installation as low as practicable, with tolerances set by the applicable standard.
Alignment and Aiming
Optical Precision Devices Need Controlled Aiming
Support We Can Provide
- Establish runway reference datum
- Verify installation coordinates
- Mechanical levelling
- Unit-to-unit elevation checks
- Vertical angle adjustment
- Azimuth verification
- Cross-runway geometry checks
- Optical signal verification
- Approach-slope confirmation
- Document installed settings
Setting Angles
For a four-unit PAPI the setting angles are normally the approach angle θ −30′, θ −10′, θ +10′ and θ +30′. A 3° path therefore gives 2°30′, 2°50′, 3°10′ and 3°30′, which is why a 10-minute graduation is the minimum useful resolution. Confirm the settings, including those for a two-unit system, against the applicable Annex 14 or FAA edition.
Tools & Coordination
A clinometer, alignment telescope and suitable PAPI alignment/check equipment can be used, depending on project methodology. Under FAA AC 150/5345-28H the PAPI system is furnished with its own aiming tool, which must read the beam-centre angle from 2° to 8° in 10-minute graduations with ±3-minute repeatability. A telescope or check stick complements that tool rather than replacing it.
Where the PAPI is associated with ILS, GLS or LPV, check the visual and non-visual references together, not independently. FAA AC 150/5340-30J specifically addresses PAPI siting against these glide paths.
Optical & Photometric Characteristics
Sharply Defined Angular Sectors
The Optical System Should Provide
- Stable colour presentation
- Clearly defined red/white transition
- Consistent vertical beam geometry
- Appropriate intensity for conditions
- Controlled azimuth coverage
- Adequate visual acquisition range
- Repeatable unit-to-unit performance
- Protection against stray light and optical degradation
Why the Transition Matters
PAPI is fundamentally angular guidance. A fixture can produce substantial output and still perform poorly if the transition sector, aiming angle or unit alignment is wrong.
FAA pilot guidance states PAPI normally provides useful vertical guidance to about ±10° of the extended runway centreline, though local conditions may reduce the effective area.
Electrical Configuration
Architecture Depends on Equipment and Airport Design
| Parameter | Engineering requirement |
|---|---|
| Supply arrangement | FAA Style A (voltage-powered, with power and control unit) or Style B (current-powered); confirm project architecture |
| Circuit type | Style B runs on a series lighting circuit (2.8–6.6 A) with isolation transformers; Style A runs from a utility voltage supply |
| Control | Local, remote or continuous-operation philosophy |
| Switching | Confirm operating and maintenance isolation |
| Intensity control | Confirm required operating levels. FAA Style A has a day mode and two night settings at about 5% and 20% of day intensity |
| Protection | Surge, fault and environmental protection as applicable. FAA-qualified units also switch the system off if a light unit tilts out of its aiming angle |
| Earthing | Verify system and installation earthing |
| Cabling | Confirm airfield-rated cable and connectors |
| Monitoring | Confirm whether health/status monitoring is required |
| Redundancy | From operational requirement and authority specification |
FAA guidance notes basic PAPI systems may operate independently through a photoelectric device for continuous operation, while others use remote control. FAA equipment is also classed by operating temperature (Class I: −35 °C to +55 °C; Class II: −55 °C to +55 °C). Take exact supply characteristics from the selected product's approved technical data.
Excessive-Tilt Protection
The FAA standard requires the system to de-energise if a light unit is displaced by a fraction of a degree from its preset aiming angle, with a 10–30 second delay to avoid nuisance trips, and the sensing must fail safe. A tripped PAPI is therefore a prompt to re-verify alignment, not just to reset the supply.
Technical Data
Confirm Against the Datasheet and Project Specification
| Parameter | Project / manufacturer value |
|---|---|
| System type | PAPI / APAPI / authority-approved configuration |
| FAA equipment designation | L-880 / L-881 where applicable |
| Number of light units | Project-specific |
| Optical technology | Project-specific |
| Light colour | Aviation red / aviation white |
| Red/white transition | FAA: within 3 minutes of arc at beam centre and 5 at beam edges, viewed at 1,000 ft (300 m); confirm against datasheet |
| FAA style and class | Style A or B; Class I or II (AC 150/5345-28H) |
| Approach angle | Project-specific; commonly 3° under FAA guidance |
| Vertical angular settings | Project-specific |
| Horizontal coverage | Project-specific |
| Photometric output | Manufacturer / applicable specification |
| Supply voltage / current | Project-specific |
| Control and intensity control | As specified |
| Dimensions | Manufacturer-specific |
| Mounting arrangement | Adjustable mounting legs with frangible couplings (FAA drawing C-6046 or equivalent) on an approved pad or foundation |
| Finish and height | FAA: International Orange finish; light unit not higher than 40 in (1 m) at its minimum mounting height |
| Operating temperature, environmental protection | Manufacturer-specific |
| Mechanical loading | Site and support design dependent |
| Cable arrangement, monitoring | Project-specific; optional |
| Alignment tolerance | Applicable standard and approved installation specification |
| Verification method | Project commissioning procedure |
Mounting & Runway Coordination
A Stable Reference Platform
Civil Interface
- Prepared mounting pad or foundation
- Precision elevation reference
- Anchor system and adjustable hardware
- Frangible mounting where required
- Drainage and cable entry protection
- Access for maintenance and alignment
- Protection against grass, soil and debris
Coordinate with runway safety-area and frangibility requirements. Position low enough to avoid unnecessary clearance risk while keeping the required optical line of sight.
Runway Interfaces
- Threshold position and displaced threshold
- Runway centreline, threshold elevation
- Longitudinal profile and transverse slope
- Approach lighting
- ILS / GLS / LPV systems
- Obstacle limitation surfaces
- Taxiway geometry, runway strip and safety areas
- Aircraft types and eye-to-wheel characteristics
ICAO material says PAPI/APAPI siting must be compatible with visual and non-visual approach guidance and account for relevant aircraft characteristics.
Performance Verification
Commission, Then Re-Verify After Changes
Initial Commissioning
- Physical coordinates, unit spacing, elevations
- Mounting stability
- Individual unit operation
- Red/white optical presentation
- Vertical aiming and azimuth
- System reference geometry
- Electrical supply and intensity operation
- Optical contamination check
- Correspondence with approved approach slope
- Record as-installed settings
After realignment or unit replacement, the authority may require a flight inspection or a notified unserviceability before the PAPI returns to service. Follow the airport procedure.
Post-Maintenance Verification
Consider re-verification after:
- Replacing a complete light unit
- Replacing or disturbing optical assemblies
- Mounting repairs or foundation movement
- Major pavement rehabilitation
- Cable or electrical modifications
- Changes to runway threshold or ILS/GLS/LPV parameters
- Significant vegetation or landscaping changes
- Reported inconsistent pilot indications
PAPI Check Stick & Alignment Equipment
Part of the Commissioning Methodology
PAPI Check StickField checking of angular performance and alignment against reference points.
ClinometerControlled angle measurement during setup and verification.
Alignment TelescopePrecision visual alignment with runway and survey references.
Mounting StandMechanical interface to establish and maintain light-unit geometry.
Select these as part of the installation and commissioning methodology, not as unrelated workshop tools.
Maintenance
Preserve Optical Accuracy, Stability and Reliability
Optical
- Dirty front windows
- Condensation
- Scratches or damage
- Discolouration
- Loss of optical definition
- Water ingress
- Degraded lamps or LEDs
- Incorrect optical assembly
Mechanical
- Mounting hardware
- Foundations
- Alignment mechanisms
- Unit levelling
- Corrosion, structural damage
- Frangible components
- Impact or movement
Electrical
- Supply voltage/current
- Cable insulation, connectors
- Isolation components, grounding
- Protection devices
- Control and monitoring
- Overheating or moisture
Site
- Vegetation
- Soil accumulation
- Construction materials
- Parked equipment
- Other obstacles in the optical field
ICAO inspection material specifically flags long grass and similar site conditions around visual approach slope indicators.
Troubleshooting
Symptoms, Causes and Checks
All units white when a mixed indication is expected
Incorrect aircraft position, unit aiming, excessive vertical setting error or optical transition problems.
Check
- Unit aiming
- Installation elevation
- Runway reference
- Vertical angle settings
- Optical condition
- Field verification procedure
All units red
Aircraft substantially below the path, or an incorrect vertical reference.
Check
- PAPI elevation
- Approach angle settings
- Unit sequencing
- Survey reference
- Actual aircraft position
Inconsistent indications between units
Unit-to-unit misalignment, differing elevations or mechanical movement.
Check
- Relative unit height
- Cross-level
- Individual aiming
- Mounting condition
- Survey control
One unit differs in colour or intensity
Optical contamination or deterioration, light-source degradation or electrical problems.
Check
- Lens/window condition
- Light source
- Power supply
- Driver/current
- Optical assembly
- Internal contamination
PAPI differs from ILS glide-path expectations
An engineering coordination issue, not simply a fixture fault.
Check
- PAPI reference position
- ILS/GLS/LPV reference data
- Threshold crossing geometry
- PAPI vertical aiming
- Runway elevation information
- Recent runway or navigation modifications
Selection Checklist
Before Specifying a PAPI System
Runway
- Designation
- Length and width
- Threshold location
- Displaced threshold, if any
- Threshold elevation
- Longitudinal and transverse profile
Aircraft
- Aircraft types using the runway
- Eye-to-wheel characteristics
- Dominant aircraft category or height group
- Required threshold crossing height
Approach
- Instrument approach type
- ILS / GLS / LPV availability
- Approved visual approach angle
- Obstacle environment and clearance
- Day/night operating conditions
Electrical
- Available supply
- Series or direct-voltage architecture
- Control system and intensity control
- Monitoring requirements
- Cable routing
Installation
- PAPI side of runway
- Physical coordinates
- Mounting arrangement
- Foundation condition, drainage
- Frangibility requirements
- Maintenance access
Verification
- Survey reference
- Alignment tools
- Commissioning method
- Photometric/optical verification
- Authority inspection requirements
- As-built documentation
What Precision AGL Solutions Can Support
From Selection to Documentation
System SelectionReview of the intended configuration against runway, aircraft and regulatory requirements.
Siting ReviewThreshold relationship, approach geometry and available installation area.
Alignment EngineeringControlled elevation, vertical angle and azimuth settings.
Electrical IntegrationSupply, control and interface requirements.
Installation SupportMounting, cabling, mechanical adjustment and site preparation.
CommissioningFunctional, alignment and performance verification.
Maintenance SupportInspection guidance, fault diagnosis, adjustment and replacement planning.
DocumentationAs-installed information, technical data, alignment records and maintenance references.
Standards & References
Governing Standards
Base design and installation on the authority and jurisdiction applicable to the aerodrome. The latest authority-approved edition governs.
ICAO
Annex 14, Volume I — Aerodromes, including current amendments and corrigenda. The ICAO Store lists the 9th Edition (July 2022) with Amendment 18. Review PAPI provisions with the associated aerodrome design, obstacle-clearance and visual-aid requirements. See also the ICAO Aerodrome Design Manual (Doc 9157) Part 4, Visual Aids, and, for India, DGCA CAR Section 4 (Aerodrome Standards).
FAA
- AC 150/5345-28H — Precision Approach Path Indicator (PAPI) Systems; issued 29 July 2019, listed as active; defines L-880/L-881, Styles A/B and Classes I/II
- AC 150/5340-30J — Design and Installation Details for Airport Visual Aids; issued 12 February 2018, listed as active; PAPI siting and installation
- Order JO 6850.2C — Visual Guidance Lighting Systems; FAA installation criteria including PAPI siting and aiming
- AC 150/5340-26C — Maintenance of Airport Visual Aid Facilities
- Engineering Brief #95 — Additional siting and survey considerations for PAPI and other visual glide slope indicators
- AIM and aeronautical information on PAPI operation, indications and normal placement
Project-Specific Authorities
- National civil aviation authority regulations
- Aerodrome certification requirements
- Airport design standards
- Approved instrument approach procedures
- Lighting control specifications
- Electrical standards
- Frangibility requirements
- Employer's requirements
FAQ
PAPI System — Frequently Asked Questions
What does a PAPI system do?
A Precision Approach Path Indicator (PAPI) gives pilots an immediate visual indication of whether they are above, on, or below the approach path, using sharply defined red and white sectors. FAA guidance describes it as a row of two or four focused light units, normally installed on the left side of the runway; ICAO Annex 14 likewise places the wing bar on the left unless that is physically impracticable.
What is the difference between FAA L-880 and L-881 PAPI?
L-880 is the standard four-unit PAPI arrangement and L-881 is the two-unit arrangement (APAPI). PAPI should be specified by the number of light units, not by bars: the term 3-bar is associated with three-bar VASI. If a brief says 2-bar or 3-bar PAPI, confirm the intended arrangement against the national aerodrome standard and project specification before equipment selection.
What do the PAPI red and white indications mean?
On a four-unit PAPI, all units white means well above the slope, three white and one red slightly above, two white and two red on or close to the slope, one white and three red slightly below, and all units red well below. A two-unit PAPI gives three sectors instead of five: both units white above the slope, both red below it, and on or close to the slope the unit nearer the runway shows red and the farther unit white.
Where is a PAPI installed and how are the units spaced?
A PAPI is normally on the left side of the runway. The FAA equipment standard (AC 150/5345-28H) is written for light units spaced 20 to 30 ft (6 to 10 m) apart, and ICAO Annex 14 requires equal spacing. Confirm the exact spacing and the distance from the runway edge in the applicable standard; FAA Engineering Brief #95 covers additional siting and survey considerations.
What approach angle and unit setting angles does a PAPI use?
The standard PAPI glideslope referenced by FAA guidance is 3 degrees, and for certain non-jet runways FAA permits considering a higher angle for obstacle clearance, subject to design requirements. For a four-unit PAPI the setting angles are normally the approach angle minus 30 minutes, minus 10 minutes, plus 10 minutes and plus 30 minutes, so a 3 degree path gives 2°30′, 2°50′, 3°10′ and 3°30′. ICAO Annex 14 also ties the setting to a minimum eye height over the threshold for the aircraft eye-to-wheel height group, so establish the angle from the approved runway design and not as a generic product setting.
Why is an obstacle survey needed before fixing the PAPI position?
ICAO Annex 14 requires an obstacle protection surface for a PAPI or APAPI. No object may penetrate it unless it is shielded by an existing object or the authority judges it will not adversely affect safety. Survey the approach for obstacles before the position and angle are fixed, and keep the check current during the life of the installation.
How is a PAPI powered and controlled?
FAA Style A equipment is voltage-powered with a power and control unit and runs from a utility voltage supply; Style B is current-powered and runs on a series lighting circuit (2.8 to 6.6 A) with isolation transformers. Style A has a day mode and two night settings at about 5% and 20% of day intensity. FAA equipment is also classed by operating temperature: Class I from -35 °C to +55 °C and Class II from -55 °C to +55 °C. Take exact supply characteristics from the selected product's approved technical data.
What is excessive-tilt protection on a PAPI?
The FAA standard requires the system to de-energise if a light unit is displaced by a fraction of a degree from its preset aiming angle, with a 10 to 30 second delay to avoid nuisance trips, and the sensing must fail safe. A tripped PAPI is therefore a prompt to re-verify alignment, not just to reset the supply.
What equipment is used to aim and check a PAPI?
A clinometer, alignment telescope and PAPI alignment or check equipment can be used, depending on project methodology. Under FAA AC 150/5345-28H the PAPI is furnished with its own aiming tool, which must read the beam-centre angle from 2° to 8° in 10-minute graduations with ±3-minute repeatability; a telescope or check stick complements that tool rather than replacing it. Where the PAPI is associated with ILS, GLS or LPV, check the visual and non-visual references together.
When must a PAPI be re-verified?
Commission it with recorded as-installed settings, then consider re-verification after replacing a light unit or optical assembly, mounting repairs or foundation movement, major pavement rehabilitation, cable or electrical modifications, changes to the runway threshold or ILS, GLS or LPV parameters, significant vegetation changes, or reported inconsistent pilot indications. After realignment or unit replacement, the authority may require a flight inspection or a notified unserviceability before the PAPI returns to service.
What do common PAPI fault indications point to?
All units white when a mixed indication is expected points to aircraft position, unit aiming, vertical setting error or optical transition problems; all units red points to an aircraft well below the path or an incorrect vertical reference. Inconsistent indications between units suggest misalignment, differing elevations or mechanical movement, and one unit differing in colour or intensity suggests optical contamination, light-source degradation or an electrical problem. A PAPI that differs from ILS glide-path expectations is an engineering coordination issue, not simply a fixture fault.
What information is needed to quote or review a PAPI project?
Useful information includes the runway layout drawing, threshold coordinates and elevations, the runway longitudinal profile, approach category, aircraft fleet or critical aircraft information, existing ILS, GLS or LPV information, an obstacle survey, existing PAPI coordinates and settings, the electrical single-line diagram, available supply parameters, the control philosophy, applicable national and airport standards, and the commissioning and acceptance procedure.
Technical Submittal
Information to Request for Quotation or Review
Useful project information includes:
- Runway layout drawing
- Threshold coordinates and elevations
- Runway longitudinal profile
- Approach category
- Aircraft fleet / critical aircraft information
- Existing ILS/GLS/LPV information
- Obstacle survey or approach-surface information
- Existing PAPI coordinates and settings, where applicable
- Electrical single-line diagram
- Available supply parameters
- Required control philosophy
- Applicable national and airport standards
- Required commissioning and acceptance procedure
Procurement Information for Indian Projects
Indian public tenders commonly ask for the documents below. State which ones your tender requires when you send the enquiry, so they are covered in the quotation.
- Manufacturer / OEM authorisation
- Country of origin and local-content declaration (for Make in India purchase preference)
- Type-test and routine-test certificates, and the FAA / ICAO / IEC compliance documents named in the specification
- Datasheets, drawings and installation instructions
- Warranty, delivery period and spares support
- GeM catalogue or tender-portal requirements, where applicable
Planning a PAPI Installation or Upgrade?
Share the runway designation, runway dimensions, threshold information, approach category, aircraft types, existing ILS/GLS/LPV information and available site layout so the appropriate system configuration and installation requirements can be assessed.
- Emailprecisionaglsolutions@gmail.com
- Websiterahulsharmaagl.in
- LinkedInPrecision AGL Solutions
- Phone+91 98214 96412
Engineering Note
PAPI is a geometrically controlled visual guidance system, not simply a row of high-intensity lights. Correct performance depends on the relationship between the light units, runway datum, threshold, approach angle, aircraft geometry and obstacle environment.
For procurement accuracy, specify the actual approved system classification, such as FAA L-880 or L-881 where applicable, rather than relying only on the terms “2-bar” or “3-bar”. FAA standards distinguish PAPI configurations by number of light units, while three-bar terminology is associated with VASI.
Final selection, siting and commissioning should be verified against the applicable aerodrome authority requirements and current approved technical documentation.
Product Disclaimer
Product availability, configuration, dimensions, electrical characteristics, photometric performance, certifications and compliance status depend on the selected manufacturer and project specification. The technical values published on this page should not be treated as a substitute for the manufacturer's current approved Technical Data Sheet.
Final selection shall be based on the approved project specification, applicable aviation standards, authority requirements, manufacturer documentation and site conditions. Use of this page is also subject to the Legal Notice, Disclaimer & Terms of Use.
Standards and editions referenced on this site are listed on the Standards Reference page.