Division 11 — PAPI / VASI Troubleshooting

01 · PAPI / VASI Faults

20 of 20 topics published

PAPI-291 PAPI Completely Off

Symptom — The entire PAPI wing bar (all units) is dark, with no red or white light visible at night despite the associated lighting circuit reportedly being energised.

Equipment / System

PAPI wing bar assembly (typically four units) and its dedicated series or multi-circuit feed from the CCR, including the local disconnect/isolation point and any photocell brightness control.

Possible Causes

HighCCR feeding the PAPI circuit tripped, off, or commanded to zero intensity

HighPrimary series or feeder cable open circuit or major fault upstream of the first unit

MedMain local isolating switch or circuit breaker at the PAPI enclosure open

MedPhotocell/brightness control system commanding the bar off in error

LowLoss of feeder power to the substation circuit supplying the PAPI panel

LowMain power supply cable to the PAPI panel de-energised upstream

Required Tools

Clamp-on series circuit ammeterTrue-RMS multimeterCCR panel status/logPAPI feed circuit diagram1000V insulation resistance tester (megger)

Safety Precautions

LOTO the circuit before any work, treating it as energised until confirmed isolated at the CCR.
Coordinate all airside access through ATC/apron control given the wing bar's position near the runway edge.

Diagnostic Procedure

ObservationCheck the ALCMS/CCR panel for the PAPI circuit's status and commanded intensity step.
ObservationConfirm whether any other runway lighting circuits are also affected, which would point to an upstream feeder or substation fault.
MeasurementMeasure the CCR output current for the PAPI circuit.
MeasurementCheck the local isolator/breaker and photocell control at the PAPI enclosure.
DecisionCCR output present but nothing downstream → local isolator or primary cable fault, proceed to trace the feed. No CCR output → route to CCR/power distribution troubleshooting.
Fault LocationIsolate the fault to the CCR, local isolator, photocell control, or primary cable.
Root CauseConfirm the root cause before re-energising the full circuit.

Test Points

CCR output current for the PAPI circuit

Local isolator/breaker state at the PAPI enclosure

Photocell/brightness control command signal

Primary cable continuity to the first unit

Root Cause Verification

After repair, confirm all units illuminate at the commanded intensity step and that the correct red/white split is observed from the approach path or with a collimating test device.

Corrective Action

Restore or repair the CCR feed to the PAPI circuit.
Replace a failed local isolator or breaker.
Correct a photocell/brightness control fault.
Repair the primary cable fault.

Preventive Action

Include PAPI circuit status in the nightly serviceability inspection.
Periodically function-test the photocell/brightness control.
Trend the CCR log for the PAPI circuit to catch a developing supply issue.

Related References

SOP: SOP-PAPI-01 (PAPI Fault Isolation Procedure), SOP-CCR-04 (CCR LOTO Procedure)

Standards: FAA AC 150/5345-28 (PAPI Systems), ICAO Annex 14 Vol I Attachment A, ICAO Doc 9157 Part 4

Diagram: PAPI circuit and enclosure layout drawing

Case Study: Division 01 — CCR Troubleshooting; Division 24 — Complete Runway Lighting Failure

Rev 0 — Initial issue

PAPI-292 One PAPI Unit Not Working

Symptom — One of the four units in the PAPI wing bar is dark while the remaining units illuminate normally, altering the red/white ratio seen on approach.

Equipment / System

Individual PAPI unit — lamp/LED module, isolation transformer or local driver, internal wiring, and base connector.

Possible Causes

HighLamp/LED failure within that specific unit

HighIsolation transformer or LED driver failure at that unit

MedL-823 connector or internal wiring fault at the unit

MedBlown internal fuse or local PSU/driver fault

LowMechanical or thermal damage inside the unit housing

LowUnit physically displaced, disconnecting internal wiring

Required Tools

True-RMS multimeter1000V insulation resistance tester (megger)Spare lamp/LED module matched to unit typeUnit access toolsPAPI unit technical manual

Safety Precautions

LOTO the circuit before opening the unit.
Coordinate airside access with ATC given the unit's position near the runway edge.
Re-secure the unit cover carefully to avoid disturbing the elevation/azimuth setting.

Diagnostic Procedure

ObservationConfirm which specific unit in the sequence is dark and note whether the adjacent units are unaffected.
MeasurementWith the circuit isolated, check voltage/continuity at the unit's isolation transformer or driver output.
MeasurementInspect the lamp/LED module and internal connector for visible failure.
DecisionUnit-level component confirmed faulty → proceed with unit repair. Fault traces to the shared circuit or affects more than one unit → route to PAPI-293.
Fault LocationIsolate the fault to the lamp/LED, transformer/driver, or connector.
Root CauseConfirm the specific failed component before replacement rather than swapping parts speculatively.

Test Points

Unit isolation transformer/driver output

Lamp/LED module continuity

L-823 connector condition

Internal wiring harness

Root Cause Verification

Re-energise and confirm the repaired unit matches the brightness and colour split of the other three units, verified visually at night or with a collimating test lamp.

Corrective Action

Replace the failed lamp/LED module.
Replace the failed isolation transformer or driver.
Repair or reseat the connector.
Re-level the unit if it was disturbed during repair.

Preventive Action

Stock spare lamp/LED modules matched to the installed PAPI type.
Include a per-unit visual check in the routine night inspection.
Trend individual unit run-hours for proactive lamp/LED replacement.

Related References

SOP: SOP-PAPI-02 (Unit-Level Fault Isolation Procedure)

Standards: FAA AC 150/5345-28, ICAO Annex 14 Vol I Attachment A

Diagram: PAPI unit internal wiring diagram

Case Study: Division 26 — Photometric & Intensity Compliance

Rev 0 — Initial issue

PAPI-293 Multiple PAPI Units Failure

Symptom — Two or more units within the same PAPI wing bar are dark or degraded simultaneously, while at least one unit remains functional, distorting the glide path indication.

Equipment / System

PAPI wing bar shared series circuit, feeder cable, or shared CCR circuit and the multiple individual units fed from it.

Possible Causes

HighShared primary series cable fault between the affected units

HighCCR at reduced output affecting all units on the shared circuit

MedCommon feeder or junction box fault

MedA batch of lamps/LED modules failing near-simultaneously from end-of-life

LowStorm or lightning-induced damage affecting several units together

LowRodent or animal damage to a buried cable run

Required Tools

Clamp-on series circuit ammeter1000V/2500V insulation resistance tester (megger)TDR / fault locatorPAPI circuit as-built drawing

Safety Precautions

LOTO the entire PAPI circuit before work, since multiple affected units point to a shared circuit.
Coordinate airside access through ATC/apron control.

Diagnostic Procedure

ObservationMap which specific units are affected and their position in the wing bar sequence.
MeasurementCheck the CCR output current for the shared circuit.
MeasurementMegger the primary cable in segments between the affected units.
DecisionFault isolated to one cable segment or junction → localised repair. Fault distributed with reduced CCR output → route to Division 01 CCR troubleshooting.
Fault LocationIsolate the fault to the cable segment, junction box, or shared driver.
Root CauseConfirm with a full circuit re-test that the fault has been fully cleared.

Test Points

CCR output current for the shared circuit

Segment-by-segment insulation resistance

Junction box condition

Affected units' individual driver/transformer readings

Root Cause Verification

Re-energise the circuit, confirm all previously affected units illuminate at the correct intensity and colour split, and monitor over the following nights.

Corrective Action

Repair or replace the faulted cable segment or junction.
Replace the affected lamp/LED modules.
Restore CCR output if the fault is source-side.

Preventive Action

Periodically megger the PAPI feeder circuit.
Inspect junction boxes for water ingress.
Stagger lamp/LED replacement to avoid batch end-of-life clustering.

Related References

SOP: SOP-PAPI-03 (Multi-Unit Circuit Fault Procedure)

Standards: IEC 60364 (insulation testing), ICAO Annex 14 Vol I

Diagram: PAPI circuit route drawing

Case Study: Division 24 — Complete Runway Lighting Failure

Rev 0 — Initial issue

PAPI-294 PAPI Wrong Indication

Symptom — Pilots report the PAPI indication does not match the aircraft's actual position on the approach path — a red/white ratio inconsistent with the true glide angle as cross-checked against other guidance.

Equipment / System

Complete PAPI wing bar — unit elevation settings, azimuth alignment, and colour-split integrity across all units.

Possible Causes

HighOne or more units mis-set in elevation angle, out of sequence with the schedule

HighUnit(s) rotated or shifted in azimuth so the observed colour split does not correspond to the true vertical angle

MedRed filter degraded or incorrect on one unit

MedGround settlement or frost heave altering the mounting platform level

LowA unit swapped into the wrong sequence position during maintenance

LowAn obstruction partially blocking one or more units' beams

Required Tools

Collimating theodolite / PAPI angle test setPrecision inclinometerAs-built elevation angle scheduleSurvey level

Safety Precautions

Notify airfield operations/NOTAM of a suspected wrong indication immediately given the flight-safety implications.
Consider a temporary PAPI unserviceable status pending verification.
LOTO before any mechanical adjustment.

Diagnostic Procedure

ObservationGather pilot reports and correlate them with the aircraft's known position using ILS glideslope or track data where available.
MeasurementVerify each unit's elevation angle setting against the as-built schedule using a collimating test set.
MeasurementVerify the wing bar's azimuth alignment against the runway centreline extended.
DecisionOne unit's angle out of tolerance → proceed to PAPI-303 for elevation correction. Whole bar misaligned or rotated → proceed to PAPI-304 for azimuth correction.
Fault LocationIsolate the fault to the specific out-of-tolerance unit(s) or the whole bar mounting.
Root CauseConfirm with a full angle survey after adjustment.

Test Points

Individual unit elevation angle vs. schedule

Wing bar azimuth vs. runway centreline

Red filter transition angle per unit

Mounting platform level/settlement

Root Cause Verification

Re-survey all units after correction, confirm each is within tolerance, and validate the indication with a ground-based verification check or follow-up flight check before restoring to service.

Corrective Action

Re-set the affected unit's elevation angle.
Realign the wing bar azimuth.
Replace a degraded filter.
Re-level the mounting platform.

Preventive Action

Include a full angle survey in the periodic calibration cycle.
Monitor the platform for ground settlement.
Lock elevation adjustment mechanisms after calibration to prevent drift.

Related References

SOP: SOP-PAPI-05 (PAPI Calibration Procedure)

Standards: ICAO Annex 14 Vol I Attachment A, ICAO Doc 9157 Part 4, FAA AC 150/5340-30

Diagram: PAPI angle schedule / as-built drawing

Case Study: Division 25 — Field Case Study Troubleshooting

Rev 0 — Initial issue

PAPI-295 PAPI Too Many White Indications

Symptom — Pilots consistently report seeing more white units than expected (e.g. three white/one red or four white) while independently confirmed to be on or near the correct glide path.

Equipment / System

Individual unit elevation angle settings, specifically the units expected to show red at the reported approach angle.

Possible Causes

HighOne or more units' elevation angle set too low, shifting the white sector into the correct-path region

HighRed filter faded or degraded, allowing more white-appearing light through the lower sector

MedColour transition mechanism (dichroic filter or red glass) misaligned within the housing

MedAn incorrect unit swapped into a position requiring a different angle step

LowMounting platform tilted forward, reducing the effective angle of all units

Required Tools

Collimating theodolite / PAPI angle test setRed filter transmittance referenceAs-built elevation angle schedule

Safety Precautions

Notify airfield operations of the suspected discrepancy.
LOTO before adjustment.

Diagnostic Procedure

ObservationConfirm the reports are consistent across multiple approaches/aircraft rather than a single anomalous report.
MeasurementVerify each unit's elevation angle against the schedule, focusing on the units expected to show red at the reported path.
MeasurementInspect the red filter condition/transmittance where a unit shows white but its angle checks correct.
DecisionAngle set too low on one or more units → re-set the angle. Filter degraded but angle correct → replace the filter.
Fault LocationIsolate the fault to the angle setting or the optical filter.
Root CauseConfirm with a post-adjustment survey.

Test Points

Elevation angle per unit vs. schedule

Red filter condition and colour transition sharpness

Mounting platform level

Root Cause Verification

Re-survey the angles, confirm the colour transition occurs at the specified vertical angle for each unit, and validate with a follow-up ground-based or flight check.

Corrective Action

Re-set the elevation angle on the affected unit(s).
Replace the degraded red filter/lens assembly.
Re-level the platform if tilt is the cause.

Preventive Action

Include red filter transmittance checks in periodic calibration.
Lock angle adjustment mechanisms after calibration.
Monitor platform level over time.

Related References

SOP: SOP-PAPI-05 (PAPI Calibration Procedure)

Standards: ICAO Annex 14 Vol I Attachment A

Diagram: PAPI angle schedule

Case Study: Division 26 — Photometric & Intensity Compliance

Rev 0 — Initial issue

PAPI-296 PAPI Too Many Red Indications

Symptom — Pilots report an excessive number of red units (e.g. three red/one white or four red) while independently confirmed to be on or near the correct approach path.

Equipment / System

Individual unit elevation angle settings, specifically the units expected to show white at the reported approach angle.

Possible Causes

HighOne or more units' elevation angle set too high, shifting the red sector into the correct-path region

HighWhite lamp/LED source dimming or failing in one or more units, making red appear dominant even at the correct angle

MedMounting platform tilted rearward, increasing the effective angle of all units

MedAn incorrect unit swapped into the wrong angle position

LowVegetation growth or an obstruction partially blocking the white portion of the beam

Required Tools

Collimating theodolite / PAPI angle test setCalibrated luminance meterAs-built elevation angle scheduleSite obstruction/vegetation survey

Safety Precautions

Notify airfield operations given the flight-safety relevance.
LOTO before adjustment.
Assess for obstruction hazards near the PAPI site during the survey.

Diagnostic Procedure

ObservationConfirm consistency of the reports across multiple approaches.
MeasurementVerify each unit's elevation angle against the schedule.
MeasurementCheck the white-source output/luminance where the angle is correct but red is still dominant.
MeasurementInspect the site for vegetation growth or obstructions in the unit's beam path.
DecisionAngle set too high → re-set. White source dim or failing → component repair. Obstruction present → clear the obstruction.
Fault LocationIsolate the fault to the angle setting, the white source, or an obstruction.
Root CauseConfirm with a post-correction survey.

Test Points

Elevation angle per unit vs. schedule

White sector luminance/intensity

Line-of-sight/obstruction survey from the touchdown zone

Root Cause Verification

Re-survey the angles and luminance, confirm the colour transition occurs at the correct vertical angle, and validate with a follow-up flight check.

Corrective Action

Re-set the elevation angle.
Replace or repair the white lamp/LED source.
Clear the obstruction/vegetation.
Re-level the platform.

Preventive Action

Schedule vegetation control around the PAPI site.
Include a red/white luminance balance check in periodic PM.
Lock angle settings after calibration.

Related References

SOP: SOP-PAPI-05, SOP-PAPI-06 (Obstruction Survey Procedure)

Standards: ICAO Annex 14 Vol I

Diagram: PAPI site obstruction survey drawing

Case Study: Division 26 — Photometric & Intensity Compliance

Rev 0 — Initial issue

PAPI-297 PAPI Indication Flickering

Symptom — One or more PAPI units flicker, pulse, or vary in brightness instead of holding a steady output at the commanded intensity step.

Equipment / System

PAPI unit lamp/LED driver, connector, and the series or feeder circuit supplying it.

Possible Causes

HighLoose or intermittent L-823 or internal connector, worsened by wind/vibration loading

HighA partially failed or overheating isolation transformer/LED driver with an intermittent internal fault

MedLED module nearing end of life with driver instability

MedIntermittent cable fault making and breaking contact rather than a solid open or short

LowCCR output instability itself rather than a unit-level fault

LowMoisture inside the unit housing causing an intermittent leakage path

Required Tools

True-RMS multimeter with min/max holdOscilloscope or power quality loggerThermal imaging cameraConnector test adaptor

Safety Precautions

Treat intermittent faults as live until proven otherwise.
LOTO the circuit before opening any unit even if it appears steady at the time of access.

Diagnostic Procedure

ObservationConfirm whether the flicker is on a single unit or several, and whether it correlates with a particular intensity step, vibration, or weather condition.
MeasurementLog CCR output current over a period spanning the reported flicker to rule out a source-side instability.
MeasurementWith the circuit isolated, inspect and re-torque the connector, and megger the transformer/driver under light mechanical flex.
MeasurementUse thermal imaging on the connector and transformer/driver during a live period to spot a hot connection.
DecisionFlicker follows the CCR current log → source-side, route to Division 01. Flicker isolated to the unit and reproducible by flexing the connector → connector or transformer/driver fault.
Fault LocationIsolate the fault to the connector, transformer/driver, lamp/LED module, or cable.
Root CauseConfirm by replacing the suspect component and re-testing under conditions that previously produced the flicker.

Test Points

Connector contact resistance

Transformer/driver under mechanical flex

CCR output current trend log

Lamp/LED module bench test

Root Cause Verification

Monitor the repaired unit over several operating cycles, including varying intensity steps, before closing out.

Corrective Action

Clean, re-grease, and properly seat the connector.
Replace a transformer/driver confirmed to have an intermittent internal fault.
Replace a failing lamp/LED module.
Repair the identified intermittent cable fault.

Preventive Action

Torque-check connectors during PM given continuous vibration exposure.
Include thermal imaging of connectors and drivers in the periodic PM cycle.
Trend CCR output logs to distinguish source-side from unit-side intermittent issues.

Related References

SOP: SOP-PAPI-01 (PAPI Fault Isolation Procedure)

Standards: FAA AC 150/5345-28, ICAO Annex 14 Vol I

Diagram: PAPI circuit layout drawing

Case Study: Division 01 — CCR Troubleshooting

Rev 0 — Initial issue

PAPI-298 PAPI Unequal Brightness

Symptom — One or more units in the wing bar appear noticeably dimmer or brighter than the others at the same commanded intensity step, without being fully dark.

Equipment / System

Individual unit lamp/LED source, driver, and optical assembly across the wing bar.

Possible Causes

HighLamp/LED degrading gradually rather than failing outright

HighMismatched replacement lamp/LED wattage or part number fitted to one unit

MedLens/filter contamination — dust, oil, or insects — reducing the output of one unit

MedDriver output drifting out of calibration

LowA unit installed with older-generation optics/LED technology than the rest of the bar

LowPartial obstruction reducing the perceived output of one unit

Required Tools

Calibrated luminance meter/photometerLamp/LED part catalogueLens cleaning kitDriver calibration tool

Safety Precautions

LOTO before unit access.
Use appropriate fall protection/lifting equipment for the unit mounting height.

Diagnostic Procedure

ObservationConfirm the brightness difference visually at night and/or with a luminance meter across all units at the same step.
MeasurementCheck the lamp/LED part number and rated output against the specification for the dim/bright unit.
MeasurementInspect and clean the lens/filter, then re-measure.
MeasurementCheck the driver output calibration.
DecisionPart mismatch → replace with the correct part. Contamination → clean and re-verify. Driver drift → recalibrate or replace the driver.
Fault LocationIsolate the fault to the source, optics, or driver.
Root CauseConfirm with a comparative luminance reading across the full bar.

Test Points

Luminance/intensity per unit at each intensity step

Lamp/LED part number verification

Lens/filter cleanliness

Driver output calibration

Root Cause Verification

Re-measure luminance across all units after correction and confirm readings fall within the acceptable balance tolerance between units.

Corrective Action

Replace with the correct-specification lamp/LED module.
Clean the lens/filter.
Recalibrate or replace the driver.

Preventive Action

Verify part numbers against specification at every replacement.
Include lens cleaning and a comparative luminance check in periodic PM.

Related References

SOP: SOP-PAPI-07 (Luminance Balance Check Procedure)

Standards: ICAO Annex 14 Vol I, FAA AC 150/5345-28

Diagram: PAPI photometric specification sheet

Case Study: Division 26 — Photometric & Intensity Compliance

Rev 0 — Initial issue

PAPI-299 PAPI Lamp Failure

Symptom — A specific PAPI unit's incandescent/halogen lamp has failed, causing the unit to go dark or noticeably dim, on a lamp-based PAPI installation.

Equipment / System

PAPI unit halogen/tungsten lamp, lamp holder, isolation transformer, and series circuit.

Possible Causes

HighLamp reached normal end of service life (filament failure)

HighVoltage/current spikes on the series circuit shortening lamp life

MedFrequent switching/thermal cycling accelerating filament fatigue

MedVibration from ground traffic or wind loading fatiguing the filament

LowIncorrect wattage/voltage lamp fitted at a previous replacement

LowPoor lamp seating causing arcing at the base

Required Tools

Spare lamps matching the specified type/wattageLamp changing toolTrue-RMS multimeterSeries circuit ammeter

Safety Precautions

LOTO before lamp replacement.
Allow the lamp to cool before handling.
Avoid touching halogen lamp glass with bare skin, as oil residue shortens lamp life.

Diagnostic Procedure

ObservationConfirm the specific unit and check the lamp for visible filament failure or blackening.
MeasurementCheck circuit voltage/current at the unit's isolation transformer to rule out an overvoltage condition.
MeasurementVerify the lamp holder contacts are not corroded or loose.
DecisionLamp confirmed failed with normal circuit parameters → routine lamp replacement. Circuit parameters abnormal → investigate the transformer/CCR for overvoltage.
Fault LocationIsolate the fault to lamp filament failure versus a supply-side overvoltage condition.
Root CauseConfirm the new lamp holds correctly and circuit parameters are normal.

Test Points

Lamp filament continuity

Unit supply voltage/current

Lamp holder contact condition

Root Cause Verification

Re-energise and confirm the replaced lamp operates at the correct brightness and colour split, and monitor for a premature repeat failure.

Corrective Action

Replace the lamp with the correct-specification part.
Clean or repair the lamp holder contacts.
Correct any overvoltage condition at the source.

Preventive Action

Track lamp run-hours for proactive group replacement.
Verify lamp specification at every replacement.
Monitor circuit voltage for anomalies.

Related References

SOP: SOP-PAPI-02 (Unit-Level Fault Isolation Procedure)

Standards: FAA AC 150/5345-28

Diagram: PAPI unit technical manual

Case Study: Division 26 — Photometric & Intensity Compliance

Rev 0 — Initial issue

PAPI-300 PAPI LED Failure

Symptom — A specific unit on an LED-based PAPI system has gone dark, dim, or shows an abnormal colour, with the LED driver reporting a fault or no output.

Equipment / System

LED-PAPI unit LED array/module, integral LED driver, and internal control wiring.

Possible Causes

HighLED array module failure — individual diode or full array

HighLED driver (constant current source) failure

MedDriver overheating due to inadequate heat sinking or blocked ventilation

MedInternal control/communication fault preventing the driver from receiving the intensity command

LowMoisture ingress into the LED module causing a short

LowEnd-of-life LED lumen depreciation beyond the acceptable threshold rather than a hard failure

Required Tools

LED driver diagnostic tool/laptop interfaceTrue-RMS multimeterThermal imaging cameraSpare LED module and driver

Safety Precautions

LOTO before opening the unit.
Discharge any driver capacitors per the manufacturer's instructions before handling.

Diagnostic Procedure

ObservationCheck the unit for complete darkness, dim output, or abnormal colour, and note any driver fault indicator/status light.
MeasurementConnect a diagnostic tool to the driver to read fault codes where supported.
MeasurementCheck the driver output voltage/current to the LED array.
MeasurementThermal image the driver and heat sink for overheating.
DecisionDriver fault code or no output to the array → replace the driver. Driver output normal but array dark → replace the LED module.
Fault LocationIsolate the fault to the LED array, driver, or control wiring.
Root CauseConfirm with a bench test of the removed component where practical.

Test Points

Driver output voltage/current to the array

Driver fault code/status

LED array continuity

Driver heat sink temperature

Root Cause Verification

Re-energise and confirm correct colour, brightness, and intensity-step response, and monitor driver temperature under normal operation.

Corrective Action

Replace the failed LED module.
Replace the failed driver.
Clear a ventilation/heat sink obstruction.
Reseal the unit against moisture ingress.

Preventive Action

Include driver diagnostic readout in periodic PM where supported.
Monitor LED lumen output trend for proactive module replacement.
Keep heat sinks clear of debris.

Related References

SOP: SOP-PAPI-08 (LED Module and Driver Replacement Procedure)

Standards: FAA AC 150/5345-28 (LED PAPI addenda)

Diagram: Manufacturer LED-PAPI technical manual

Case Study: Division 26 — Photometric & Intensity Compliance

Rev 0 — Initial issue

PAPI-301 PAPI Optical Failure

Symptom — A unit's beam pattern, colour transition, or beam spread is abnormal even though the lamp/LED source itself is confirmed functional, pointing to a fault in the optical assembly.

Equipment / System

PAPI unit optical assembly — primary Fresnel/collimating lens, red filter/dichroic element, internal reflector, and optical housing.

Possible Causes

HighCracked, chipped, or missing primary lens altering the beam spread

HighRed filter/dichroic element cracked, delaminated, or displaced from its mounting

MedInternal reflector misaligned or corroded, reducing beam collimation

MedCondensation or contamination between optical elements scattering the beam

LowOptical assembly loosened by vibration, shifting the colour transition edge

LowUV degradation clouding the lens and reducing overall transmittance

Required Tools

Optical inspection lightCollimating theodolite / PAPI angle test setReplacement lens/filter assemblyTorque driver for optic mounting hardware

Safety Precautions

LOTO before opening the optical chamber.
Handle optical glass/lens components carefully to avoid further damage.
Reseal the housing to manufacturer specification after work.

Diagnostic Procedure

ObservationConfirm the lamp/LED source is functional and rule out a source-level fault first.
MeasurementInspect the primary lens for cracks, chips, or missing sections.
MeasurementInspect the red filter/dichroic element for cracking, delamination, or displacement.
MeasurementVerify the internal reflector alignment and condition.
DecisionLens/filter physically damaged → replace the optical component. Reflector misaligned → realign and re-secure. Contamination present → clean and reseal.
Fault LocationIsolate the fault to the lens, filter, reflector, or housing seal.
Root CauseConfirm the beam pattern and colour transition after repair using a collimating test set.

Test Points

Lens integrity and clarity

Red filter/dichroic condition and mounting

Reflector alignment

Beam pattern via collimating test set

Root Cause Verification

Re-survey the unit's elevation angle and colour transition after optical repair, and confirm the beam pattern matches specification.

Corrective Action

Replace the damaged lens or filter assembly.
Realign and re-secure the reflector.
Clean the internal optical surfaces and reseal the housing.

Preventive Action

Include optical assembly inspection in periodic PM.
Reseal housings with fresh gasket material to prevent condensation ingress.
Protect stored spare optics from UV exposure.

Related References

SOP: SOP-PAPI-09 (Optical Assembly Inspection and Replacement Procedure)

Standards: ICAO Doc 9157 Part 4, FAA AC 150/5345-28

Diagram: PAPI unit optical assembly drawing

Case Study: Division 26 — Photometric & Intensity Compliance

Rev 0 — Initial issue

PAPI-302 PAPI Alignment Error

Symptom — The PAPI wing bar as a whole, or individual units within it, are found out of tolerance during a routine or triggered survey, covering both elevation and azimuth deviations together.

Equipment / System

Complete PAPI wing bar mounting platform, individual unit levelling frames, and site survey reference points.

Possible Causes

HighGround settlement or frost heave shifting the mounting platform

HighA unit disturbed during maintenance and not re-surveyed before returning to service

MedMounting hardware loosened by vibration allowing gradual drift

MedSnow plough, vehicle strike, or wind-storm impact shifting a unit or the platform

LowIncorrect initial commissioning survey

LowSite survey reference monuments themselves disturbed, giving a false alignment reading

Required Tools

Collimating theodolite / PAPI angle test setPrecision level/inclinometerSite survey reference drawingTorque driver for mounting hardware

Safety Precautions

LOTO before adjustment.
Notify airfield operations if any unit is taken out of service during correction.
Coordinate airside access through ATC/apron control.

Diagnostic Procedure

ObservationReview the periodic calibration record and any recent maintenance or impact events at the site.
MeasurementSurvey each unit's elevation angle and the wing bar's azimuth against the as-built reference.
MeasurementCheck the mounting platform for visible settlement, tilt, or physical disturbance.
DecisionDeviation traced to one unit → proceed to PAPI-303/PAPI-304 for the specific correction. Deviation affects the whole platform → investigate a foundation/settlement issue.
Fault LocationIsolate the fault to the individual unit levelling frame or the shared mounting platform.
Root CauseConfirm with a full post-adjustment survey referenced to the original site monuments.

Test Points

Elevation angle per unit

Wing bar azimuth vs. runway centreline extended

Mounting platform level and settlement

Site survey reference monument condition

Root Cause Verification

Re-survey all units after correction against the as-built reference, confirm all are within tolerance, and validate with a follow-up inspection or flight check.

Corrective Action

Re-set individual unit angles.
Realign the wing bar azimuth.
Correct the platform level or address foundation settlement.

Preventive Action

Schedule a full angle and azimuth survey on a defined periodic interval.
Re-survey any unit disturbed by maintenance before returning it to service.
Monitor the platform for settlement over time.

Related References

SOP: SOP-PAPI-05 (PAPI Calibration Procedure)

Standards: ICAO Annex 14 Vol I Attachment A, ICAO Doc 9157 Part 4

Diagram: PAPI as-built angle and azimuth schedule

Case Study: Division 25 — Field Case Study Troubleshooting

Rev 0 — Initial issue

PAPI-303 PAPI Elevation Angle Error

Symptom — Survey or flight check confirms one or more units are set to the wrong vertical (elevation) angle, outside the tolerance specified in the angle schedule for that unit's position in the sequence.

Equipment / System

Individual PAPI unit elevation adjustment mechanism (tilt screw/worm gear) and its locking hardware.

Possible Causes

HighElevation adjustment mechanism not properly locked after a previous calibration, allowing drift under vibration

HighIncorrect angle set during commissioning or a prior maintenance visit

MedAdjustment mechanism worn or damaged, unable to hold the set angle

MedUnit's levelling frame disturbed during a lamp/LED or optical replacement without re-survey

LowFoundation/platform settlement changing the effective angle even though the mechanism itself is unchanged

Required Tools

Collimating theodolite / PAPI angle test setPrecision inclinometerAs-built elevation angle scheduleTorque driver

Safety Precautions

LOTO before adjustment.
Support the unit securely while the elevation mechanism is unlocked to prevent uncontrolled movement.

Diagnostic Procedure

ObservationIdentify which unit(s) and confirm the required angle from the as-built schedule for that specific sequence position.
MeasurementSurvey the current elevation angle using a collimating theodolite.
MeasurementInspect the adjustment mechanism and locking hardware for wear or looseness.
DecisionAngle out of tolerance with a sound mechanism → re-set and re-lock. Mechanism worn or damaged → replace the adjustment hardware.
Fault LocationIsolate the fault to an angle setting error versus mechanism condition.
Root CauseConfirm with a re-survey after adjustment and locking.

Test Points

Elevation angle vs. schedule for that unit's sequence position

Adjustment mechanism condition and locking torque

Colour transition angle observed via collimating set

Root Cause Verification

Re-survey the corrected unit, confirm the angle and colour transition fall within tolerance, and re-check after 24–48 hours to confirm the setting has held.

Corrective Action

Re-set the elevation angle to the schedule value and torque the locking hardware.
Replace a worn or damaged adjustment mechanism.

Preventive Action

Torque-check and witness-mark elevation locks during periodic PM.
Always re-survey a unit after any maintenance that disturbs its mounting.

Related References

SOP: SOP-PAPI-05 (PAPI Calibration Procedure)

Standards: ICAO Annex 14 Vol I Attachment A, FAA AC 150/5345-28

Diagram: PAPI elevation angle schedule

Case Study: Division 26 — Photometric & Intensity Compliance

Rev 0 — Initial issue

PAPI-304 PAPI Azimuth Alignment Error

Symptom — Survey confirms the PAPI wing bar, or an individual unit, is rotated out of tolerance relative to the runway centreline extended, giving an accurate indication only when the aircraft is off the extended centreline.

Equipment / System

PAPI wing bar mounting platform and its azimuth reference/locking hardware.

Possible Causes

HighMounting platform rotated during installation or a prior maintenance visit without a proper azimuth reference

HighAzimuth locking hardware loosened by vibration or ground disturbance

MedVehicle or snow plough strike rotating the platform

MedSurvey reference points used for the original azimuth setting have since been disturbed

LowFoundation movement rotating the platform slightly over time

Required Tools

Theodolite referenced to the runway centreline extendedAzimuth locking hardwareAs-built site survey drawing

Safety Precautions

LOTO before adjustment.
Coordinate airside access and notify airfield operations if the unit is taken out of service.

Diagnostic Procedure

ObservationReview the as-built azimuth reference and any recent site disturbance or impact events.
MeasurementSurvey the current azimuth of the wing bar against the runway centreline extended using a theodolite.
MeasurementInspect the azimuth locking hardware for looseness or damage.
DecisionAzimuth out of tolerance with sound hardware → re-align and re-lock. Hardware damaged → replace.
Fault LocationIsolate the fault to an azimuth setting error versus locking hardware condition.
Root CauseConfirm with a re-survey after correction.

Test Points

Wing bar azimuth vs. runway centreline extended

Azimuth locking hardware condition

Individual unit azimuth consistency across the bar

Root Cause Verification

Re-survey the corrected azimuth, confirm it is within tolerance, and validate the indication with a follow-up flight check where practical.

Corrective Action

Re-align the wing bar to the runway centreline extended and re-torque the locking hardware.
Replace damaged locking hardware.
Re-establish disturbed survey reference points.

Preventive Action

Protect survey reference monuments near the PAPI site.
Include azimuth verification in the periodic calibration cycle.
Witness-mark locking hardware after each calibration.

Related References

SOP: SOP-PAPI-05 (PAPI Calibration Procedure)

Standards: ICAO Annex 14 Vol I Attachment A, ICAO Doc 9157 Part 4

Diagram: PAPI site azimuth survey drawing

Case Study: Division 25 — Field Case Study Troubleshooting

Rev 0 — Initial issue

PAPI-305 PAPI Water Ingress

Symptom — Moisture, condensation, or standing water is found inside a PAPI unit housing during inspection, or is suspected due to fogged optics, corrosion, or an intermittent electrical fault.

Equipment / System

PAPI unit housing, door/access seals, cable entry glands, and internal drainage provisions.

Possible Causes

HighDegraded or missing door/access seal gasket allowing moisture entry

HighCable entry gland not properly sealed after a previous maintenance visit

MedBlocked or missing internal drain path allowing condensation to accumulate

MedHeater element failure allowing normal condensation to persist instead of evaporating

LowHousing physically damaged, creating a direct entry point

LowGround/surface water pooling around the unit base during heavy rain

Required Tools

Moisture detection meter1000V insulation resistance tester (megger)Replacement gasket/seal kitCable gland sealantDrain-clearing tool

Safety Precautions

LOTO before opening the housing.
Treat internal components as wet/degraded until insulation resistance is verified.
Avoid re-energising a unit with visible standing water inside.

Diagnostic Procedure

ObservationInspect the unit for fogged optics, visible moisture, or corrosion at the next scheduled or triggered access.
MeasurementMegger the internal wiring and lamp/LED driver before re-energising.
MeasurementInspect door seals, cable glands, and drain paths to identify the entry point.
DecisionInsulation resistance acceptable → dry out, reseal, and return to service. Insulation resistance degraded → proceed to component-level fault isolation before re-energising.
Fault LocationIsolate the specific seal, gland, or drain failure providing the entry point.
Root CauseConfirm the unit is fully dry and resealed before closing out.

Test Points

Insulation resistance of internal wiring/driver

Door and access seal condition

Cable gland seal integrity

Internal drain path patency

Root Cause Verification

After drying and resealing, re-megger, re-energise, and monitor the unit over subsequent wet-weather cycles to confirm the entry point has been eliminated.

Corrective Action

Replace degraded door/access seals.
Reseal cable entry glands.
Clear or restore the internal drain path.
Repair housing damage.

Preventive Action

Include seal and drain inspection in the periodic PM cycle.
Replace gaskets proactively on a defined interval.
Ensure surface grading directs water away from unit bases.

Related References

SOP: SOP-PAPI-10 (Housing Seal and Moisture Inspection Procedure)

Standards: FAA AC 150/5345-28

Diagram: PAPI unit housing drawing

Case Study: Division 26 — Photometric & Intensity Compliance

Rev 0 — Initial issue

PAPI-306 PAPI Heater Failure

Symptom — A unit's internal anti-condensation/anti-icing heater element is confirmed or suspected failed, typically presenting as recurring fogged optics or ice formation on the lens during cold or humid conditions.

Equipment / System

PAPI unit internal heater element (lens or housing heater) and its control/thermostat circuit.

Possible Causes

HighHeater element burned out or open-circuit

HighHeater control thermostat/sensor failed, keeping the heater off when required

MedHeater supply fuse or breaker tripped

MedCorroded or loose heater wiring connection

LowHeater rated incorrectly for the unit at a previous replacement

LowHeater circuit sharing a fault path with the main lamp/LED circuit

Required Tools

True-RMS multimeterHeater element resistance reference valueThermal imaging cameraSpare heater element

Safety Precautions

LOTO before accessing the heater circuit.
Allow the unit to cool if recently energised before handling internal components.

Diagnostic Procedure

ObservationConfirm the recurring fogging or icing pattern and correlate it with weather conditions.
MeasurementCheck heater element resistance against the reference value with the circuit isolated.
MeasurementCheck the heater control/thermostat circuit and supply fuse.
MeasurementThermal image the unit during a cold/humid period to confirm whether the heater is drawing current.
DecisionHeater element open-circuit → replace the element. Control/thermostat fault → replace the control component.
Fault LocationIsolate the fault to the heater element, control circuit, or supply fuse.
Root CauseConfirm the heater draws the correct current after repair.

Test Points

Heater element resistance/continuity

Heater control/thermostat operation

Heater supply fuse/breaker

Thermal image of the unit under cold conditions

Root Cause Verification

Monitor the unit through a subsequent cold or humid period and confirm no recurrence of fogging or icing.

Corrective Action

Replace the failed heater element or control component.
Repair heater wiring connections.
Replace the supply fuse and investigate the cause of the trip.

Preventive Action

Include a heater functional test in the periodic PM cycle, particularly before the cold season.
Verify heater specification matches the unit at every replacement.

Related References

SOP: SOP-PAPI-11 (Heater Circuit Test Procedure)

Standards: Manufacturer PAPI unit technical manual

Diagram: PAPI unit heater circuit diagram

Case Study: Division 26 — Photometric & Intensity Compliance

Rev 0 — Initial issue

PAPI-307 PAPI Temperature Alarm

Symptom — The remote monitoring system reports an over-temperature alarm for a PAPI unit or its driver/enclosure, without an accompanying loss of light output.

Equipment / System

PAPI unit or driver temperature sensor and its link into the remote monitoring system.

Possible Causes

HighGenuine overheating from a blocked or degraded heat sink or restricted ventilation

HighDriver operating at excessive current due to a partial internal fault, generating extra heat without yet causing a visible output fault

MedAmbient temperature extreme pushing the unit close to its rated limit while still functioning correctly

MedTemperature sensor itself faulty, giving a false high reading

LowMonitoring system alarm threshold set too conservatively for the site's climate

Required Tools

Thermal imaging cameraTrue-RMS multimeter/clamp ammeterManufacturer temperature sensor reference dataMonitoring system diagnostic access

Safety Precautions

LOTO before internal inspection.
Allow the unit to cool before opening if a genuine over-temperature condition is suspected.

Diagnostic Procedure

ObservationReview the alarm history and correlate it with ambient weather conditions and time of day.
MeasurementThermal image the unit/driver to confirm the actual temperature against the sensor's reported value.
MeasurementCheck driver current draw against the rated specification.
DecisionGenuine overheating confirmed → investigate ventilation/heat sink or driver fault. Sensor reading inconsistent with the thermal image → replace or recalibrate the sensor.
Fault LocationIsolate the fault to ventilation/heat sink obstruction, driver fault, or sensor fault.
Root CauseConfirm the temperature returns to the normal range after correction.

Test Points

Unit/driver actual temperature via thermal imaging

Temperature sensor reading vs. actual

Driver current draw

Ventilation/heat sink condition

Root Cause Verification

Monitor the unit's temperature trend over subsequent operating cycles, including peak ambient conditions, to confirm the alarm does not recur.

Corrective Action

Clear the ventilation/heat sink obstruction.
Replace a faulty driver.
Replace or recalibrate the temperature sensor.
Adjust the monitoring threshold if found to be set inappropriately for the site.

Preventive Action

Include heat sink and ventilation inspection in periodic PM.
Trend temperature alarm history to catch a developing driver fault before it causes an output failure.

Related References

SOP: SOP-PAPI-12 (Temperature Monitoring and Alarm Response Procedure)

Standards: Manufacturer LED-PAPI technical manual

Diagram: PAPI unit thermal management drawing

Case Study: Division 26 — Photometric & Intensity Compliance

Rev 0 — Initial issue

PAPI-308 PAPI Power Supply Failure

Symptom — A PAPI unit or the whole wing bar loses power at the local supply level even though the upstream circuit/CCR is confirmed energised and outputting correctly.

Equipment / System

PAPI unit's isolation transformer (series-circuit units) or local power supply/driver input stage (LED units), and the local wiring between the circuit and the unit.

Possible Causes

HighIsolation transformer primary or secondary winding failure

HighLED driver input stage failure

MedBlown internal fuse at the unit

MedLocal supply wiring fault between the circuit tap and the unit

LowCorroded or loose connection at the unit's power input terminal

LowA mismatched or incorrectly rated transformer/PSU installed at a previous replacement

Required Tools

True-RMS multimeter1000V insulation resistance tester (megger)Clamp ammeterSpare transformer/PSU matched to unit type

Safety Precautions

LOTO before working on the local supply.
Confirm isolation at both the CCR/circuit and the unit before handling.

Diagnostic Procedure

ObservationConfirm the upstream circuit/CCR is energised and outputting correctly, ruling out a circuit-level cause.
MeasurementCheck voltage at the unit's power input terminal with the circuit live.
MeasurementWith the circuit isolated, megger the local transformer or check the driver's input fuse/stage.
DecisionVoltage present at the terminal but not at the load → internal unit fault. No voltage at the terminal → local wiring/connection fault.
Fault LocationIsolate the fault to the transformer/PSU, internal fuse, or local wiring.
Root CauseConfirm correct voltage and current at the unit after repair.

Test Points

Voltage at unit power input terminal

Transformer/PSU primary and secondary readings

Internal fuse condition

Local wiring continuity

Root Cause Verification

Re-energise and confirm the unit operates at the correct brightness and colour split across all intensity steps, and re-check after a short operating period.

Corrective Action

Replace the failed transformer or local PSU.
Replace a blown internal fuse.
Repair the local wiring connection.

Preventive Action

Verify transformer/PSU rating matches the unit specification at every replacement.
Include a local supply voltage check in periodic PM.

Related References

SOP: SOP-PAPI-13 (Local Power Supply Fault Procedure)

Standards: FAA AC 150/5345-28

Diagram: PAPI unit wiring diagram

Case Study: Division 01 — CCR Troubleshooting

Rev 0 — Initial issue

PAPI-309 PAPI Communication Failure

Symptom — The remote monitoring system shows a lost or stale status for a PAPI unit's brightness/photocell control or driver telemetry, even though the unit continues to display light on visual inspection (or the reverse — status shows normal but the unit is confirmed dark).

Equipment / System

PAPI unit's local monitoring/communication interface (photocell status, driver telemetry, or fieldbus link) and its connection back to the monitoring system.

Possible Causes

HighCommunication cable or fieldbus connector fault between the unit and the monitoring panel

HighLocal communication module/interface card failure at the unit

MedMonitoring system configuration pointing to the wrong unit address

MedPower loss to the communication interface separate from the main lighting circuit

LowElectromagnetic interference or a nearby fault disrupting the data link

LowSoftware/firmware fault in the monitoring system itself rather than the field unit

Required Tools

Fieldbus/communication test tool or diagnostic laptopTrue-RMS multimeterCable tracerMonitoring system configuration access

Safety Precautions

LOTO before opening the unit's communication interface.
Coordinate with the monitoring system administrator before altering configuration.

Diagnostic Procedure

ObservationCompare the reported monitoring status against a direct visual/physical check of the unit.
MeasurementCheck the communication cable/connector for continuity and correct termination.
MeasurementVerify power to the local communication interface.
DecisionStatus disagrees with physical reality → communication fault, proceed with interface/cable investigation. Status agrees with physical reality → re-classify as the underlying lighting fault type.
Fault LocationIsolate the fault to the cable/connector, interface module, or monitoring system configuration.
Root CauseConfirm the reported status matches the physical state after repair.

Test Points

Communication cable/connector continuity

Communication interface module power and status

Monitoring system unit address/configuration

Root Cause Verification

After repair, confirm the monitoring system status tracks correctly through a full intensity-step change and a subsequent power cycle.

Corrective Action

Repair or replace the communication cable/connector.
Replace the local communication interface module.
Correct the monitoring system configuration/address.

Preventive Action

Include communication link verification against physical status in periodic PM.
Document unit addressing clearly in the monitoring system configuration record.

Related References

SOP: SOP-PAPI-14 (Remote Monitoring Verification Procedure)

Standards: ALCMS/monitoring system technical manual

Diagram: PAPI monitoring system architecture diagram

Case Study: Division 01 — CCR Troubleshooting

Rev 0 — Initial issue

PAPI-310 PAPI Photometric Non-Compliance

Symptom — A photometric survey finds the PAPI wing bar, or one or more units within it, outputting light intensity, colour, or beam spread outside the tolerances specified in the applicable standard, even though the units appear to operate normally.

Equipment / System

Complete PAPI unit optical and electrical output — lamp/LED source, driver/transformer output, and optical assembly — evaluated against the photometric specification.

Possible Causes

HighGradual lamp/LED lumen depreciation below the specified minimum intensity

HighDriver/transformer output drifting below its rated current, reducing overall brightness

MedLens/filter contamination or degradation reducing transmittance

MedColour coordinates drifting outside the ICAO/FAA chromaticity boundary due to filter ageing

LowIncorrect intensity step commanded at the CCR for prevailing conditions rather than a unit fault

LowBeam spread altered by a damaged or incorrectly seated optical assembly

Required Tools

Calibrated photometer/luminance meterColour coordinate/chromaticity meterCCR intensity step logPhotometric specification reference (ICAO/FAA)

Safety Precautions

LOTO before any component-level correction identified by the survey.
Coordinate the survey with airfield operations if it requires a ground stop or runway closure.

Diagnostic Procedure

ObservationReview the photometric survey report to identify which unit(s) and which parameter — intensity, colour, or beam spread — failed.
MeasurementRe-verify the affected unit's output with a calibrated photometer and chromaticity meter under controlled conditions.
MeasurementCheck the CCR intensity step commanded at the time of the original survey.
DecisionIntensity below minimum → investigate the lamp/LED, driver, or lens contamination. Colour outside boundary → investigate the filter condition.
Fault LocationIsolate the fault to the source, driver, or optical component.
Root CauseConfirm restored compliance with a repeat photometric measurement.

Test Points

Measured intensity vs. ICAO/FAA minimum for the commanded step

Chromaticity coordinates vs. colour boundary

Beam spread/pattern vs. specification

CCR commanded intensity step at time of survey

Root Cause Verification

Repeat the photometric measurement after correction and confirm all affected units meet the specified intensity, colour, and beam spread tolerances, then schedule a follow-up flight check if required.

Corrective Action

Replace the lamp/LED source.
Replace or recalibrate the driver/transformer.
Clean or replace the lens/filter assembly.
Realign the optical assembly.

Preventive Action

Schedule periodic photometric surveys ahead of the interval required by the applicable standard.
Trend intensity and chromaticity readings over time to catch gradual drift before it becomes non-compliant.

Related References

SOP: SOP-PAPI-15 (Photometric Survey and Compliance Procedure)

Standards: ICAO Annex 14 Vol I Attachment A, FAA AC 150/5345-28

Diagram: PAPI photometric specification sheet

Case Study: Division 26 — Photometric & Intensity Compliance

Rev 0 — Initial issue

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Frequently Asked Questions

Quick answers about PAPI / VASI troubleshooting in the AGL Troubleshooting Atlas.

Q1What does Division 11 of the AGL Troubleshooting Atlas cover?

Division 11 is the PAPI / VASI Troubleshooting reference. It publishes 20 diagnostic topics, PAPI-291 to PAPI-310, for PAPI / VASI faults on airfield ground lighting systems.

Q2What information does each topic include?

Every topic follows the same diagnostic record: the symptom, equipment/system, possible causes ranked by likelihood (high, medium or low), required tools, safety precautions, diagnostic procedure, test points, root cause verification, corrective action, preventive action and related references (SOPs, standards, diagrams and case studies).

Q3Which PAPI / VASI faults are covered?

The 20 topics are PAPI-291 to PAPI-310: PAPI Completely Off; One PAPI Unit Not Working; Multiple PAPI Units Failure; PAPI Wrong Indication; PAPI Too Many White Indications; PAPI Too Many Red Indications; PAPI Indication Flickering; PAPI Unequal Brightness; PAPI Lamp Failure; PAPI LED Failure; PAPI Optical Failure; PAPI Alignment Error; PAPI Elevation Angle Error; PAPI Azimuth Alignment Error; PAPI Water Ingress; PAPI Heater Failure; PAPI Temperature Alarm; PAPI Power Supply Failure; PAPI Communication Failure; PAPI Photometric Non-Compliance.

Q4How does a diagnostic procedure begin in Division 11?

Each procedure starts with observation before any intervention. For example, PAPI-291 (PAPI Completely Off) begins: Check the ALCMS/CCR panel for the PAPI circuit's status and commanded intensity step.

Q5What safety precautions apply when troubleshooting PAPI / VASI?

Each topic lists its own precautions. For example, PAPI-291 (PAPI Completely Off) starts with: LOTO the circuit before any work, treating it as energised until confirmed isolated at the CCR.

Q6Which SOPs are referenced in Division 11?

Related references in the topics include SOP-PAPI-01 (PAPI Fault Isolation Procedure), SOP-CCR-04 (CCR LOTO Procedure), SOP-PAPI-02 (Unit-Level Fault Isolation Procedure), SOP-PAPI-03 (Multi-Unit Circuit Fault Procedure), SOP-PAPI-05 (PAPI Calibration Procedure), SOP-PAPI-06 (Obstruction Survey Procedure), SOP-PAPI-07 (Luminance Balance Check Procedure) and SOP-PAPI-08 (LED Module and Driver Replacement Procedure), and 7 more.

Q7Which standards are referenced in the PAPI / VASI topics?

Where a standard applies, it appears in the topic's Related References. Those cited in this division include FAA AC 150/5345-28, ICAO Annex 14 Vol I Attachment A, ICAO Doc 9157 Part 4, IEC 60364, ICAO Annex 14 Vol I and FAA AC 150/5340-30.

Q8How can I find a specific fault in Division 11 quickly?

Use the search box at the top of the page to filter the 20 published topics by code, fault name or keyword; matching topics open automatically. Each diagnostic record can also be downloaded as a Word (.doc) file.