The dedicated failure-classification section for Precision Approach Path Indicator (PAPI) and Abbreviated PAPI (APAPI) systems — covering not only PAPI hardware failures, but also the alignment, elevation, azimuth, beam-angle and photometric failures that can leave a PAPI unit technically energized yet operationally incorrect. “Light is ON” does not necessarily mean “PAPI is performing correctly.”
Key principle — Division 11 separates equipment failure from guidance-performance failure. A PAPI can be energized and apparently operational while its optical alignment or photometric output has already deteriorated. Every record should answer: what failed → how did it fail → why did it fail → what evidence confirmed it → what was the effect on approach guidance → how was it corrected → how can recurrence be prevented?
Failure of a complete PAPI unit resulting in loss of its intended lighting or indication function.
Failure of an APAPI unit resulting in loss or degradation of the APAPI indication.
Use the same basic failure path as PAPI (PAF-01), while recording the specific APAPI configuration.
Failure or burnout of the lamp used in a PAPI/APAPI lighting unit.
Failure of the LED light source within an LED-based PAPI/APAPI unit.
Failure of the electronic driver controlling the lamp/LED light source.
Loss or abnormality of the electrical supply required for PAPI/APAPI operation.
Failure of cabling supplying or controlling PAPI/APAPI equipment.
Cross-reference with Division 02 — Electrical Failures and Division 05 — Cable & Connector Failures where applicable.
Failure of electrical connectors associated with the PAPI/APAPI system.
Cross-reference with Division 05 — Cable & Connector Failures.
Contamination of the optical window that affects light transmission or beam quality.
Physical damage or deterioration of optical components affecting the PAPI/APAPI beam.
PAPI/APAPI unit is not correctly aligned according to the applicable installation/alignment requirement.
Verify unit orientation, elevation, azimuth, reference datum and alignment condition.
Incorrect vertical/elevation positioning of a PAPI/APAPI unit or its optical reference.
Compare actual elevation against the approved/required reference.
Incorrect horizontal orientation of a PAPI/APAPI unit.
The actual PAPI/APAPI beam angle deviates from the intended/required beam-angle setting.
Alignment error (PAF-11) describes the physical alignment condition. Beam-angle deviation describes the resulting optical/angular performance. Both can therefore be recorded in the same failure chain.
Physical movement of the PAPI/APAPI structure or mounting arrangement from its intended position.
Movement or settlement of the foundation supporting the PAPI/APAPI installation.
Cross-reference with Division 06 — Mechanical & Structural Failures where appropriate.
Entry of moisture into the PAPI/APAPI unit or associated electrical/optical components.
Cross-reference with Division 09 — Environmental Failures.
Failure of internal electrical wiring within a PAPI/APAPI unit.
Failure of the communication or control function associated with PAPI/APAPI equipment where such functionality is provided.
Cross-reference with Division 07 — Control System Failures where applicable.
PAPI/APAPI provides an indication that does not correctly represent the intended approach-path condition.
Determine whether the incorrect indication is caused by:
PAPI/APAPI operation repeatedly becomes unavailable or abnormal and subsequently returns to normal without a stable permanent correction.
PAPI/APAPI continues to operate but its measured optical performance deteriorates from the required/expected condition.
Where applicable, compare:
This category is particularly important because a PAPI can be energized and apparently operational while its performance has already deteriorated.
Standard record structure, failure-chain relationships, diagnostic matrix, RCA hierarchy, RCA linkage, evidence layer and severity scheme that apply across all 22 Division 11 failure topics.
Every Division 11 failure should ideally be converted into a standard failure record with the following fields:
Identification
Technical Condition
Alignment
Photometry
RCA
Corrective Action
Verification & Reliability
Division 11 becomes much more valuable when the database captures relationships between failure modes rather than treating each as isolated.
| No. | Failure | Primary Investigation |
|---|---|---|
| 1 | PAPI unit failure | Complete unit condition |
| 2 | APAPI unit failure | APAPI unit condition |
| 3 | Lamp failure | Lamp/output |
| 4 | LED failure | LED/output |
| 5 | Driver failure | Driver/input/output |
| 6 | Power-supply failure | Supply path |
| 7 | Cable failure | Cable continuity/insulation |
| 8 | Connector failure | Connection/contact |
| 9 | Optical-window contamination | Optical condition |
| 10 | Optical damage | Optical component condition |
| 11 | Alignment error | Overall alignment |
| 12 | Elevation error | Vertical reference |
| 13 | Azimuth error | Horizontal reference |
| 14 | Beam-angle deviation | Optical/angular performance |
| 15 | Structural movement | Physical stability |
| 16 | Foundation settlement | Civil/foundation condition |
| 17 | Moisture ingress | Sealing/internal condition |
| 18 | Internal wiring failure | Internal electrical circuit |
| 19 | Communication/control failure | Control/communication |
| 20 | Incorrect PAPI indication | Indication verification |
| 21 | Intermittent PAPI operation | Recurrence/intermittency |
| 22 | Photometric-performance degradation | Photometric measurement/trend |
For PAPI/APAPI, the database distinguishes between equipment failure and guidance-performance failure. For example:
This distinction is important because “light is ON” does not necessarily mean “PAPI is performing correctly.”
Division 11 links every failure to the Root Cause Analysis Database. The most relevant RCA categories for PAPI/APAPI failures are:
Every failure receives a severity classification, plus operational-impact tagging:
Critical / Safety-Critical — immediate operational or safety risk
Major / Operationally Critical — significant availability impact
Moderate — reduced performance, not yet critical
Minor / Non-Critical — limited or no operational effect
Degradation / Intermittent / Latent — developing or hidden fault
Visual Evidence
Technical Evidence
The Troubleshooting Atlas answers “I have a fault now — how do I diagnose and fix it?” The Failure Database answers “this failure happened — what happened, why, what evidence proves it, what was done, and how do we stop it recurring?” Kept strictly separate, then linked end-to-end, the two form a genuine AGL Failure Intelligence Engine rather than a simple fault list. Division 11 connects directly with Division 01 Lighting Fixture Failures, Division 02 Electrical Failures, Division 05 Cable & Connector Failures, Division 06 Mechanical & Structural Failures, Division 07 Control System Failures, Division 09 Environmental Failures, Division 18 Maintenance-Induced Failures, Division 19 Product & Component Reliability, Division 21 RCA and Division 23 Reliability Trend Analysis.
Quick answers about PAPI and APAPI failures, as covered in Division 11 of the AGL Failure Database.
Division 11 covers failures of Precision Approach Path Indicator (PAPI) and Abbreviated PAPI (APAPI) systems. It contains 22 published topics (PAF-01 to PAF-22) spanning unit, electrical, optical, alignment, structural, environmental, control and performance failures.
PAPI unit failure, APAPI unit failure, lamp, LED, driver, power-supply, cable and connector failure, optical-window contamination, optical damage, alignment, elevation and azimuth error, beam-angle deviation, structural movement, foundation settlement, moisture ingress, internal wiring failure, communication/control failure, incorrect PAPI indication, intermittent PAPI operation and photometric-performance degradation.
They fall into six groups: PAPI/APAPI Equipment Failures (2 topics), Electrical & Component Failures (6), Optical & Alignment Failures (6), Structural & Environmental Failures (3), Control & Operational Failures (4) and Performance Failure (1).
No. The database distinguishes equipment failure from guidance-performance failure because “light is ON” does not necessarily mean “PAPI is performing correctly”. The hierarchy runs from equipment level (for example LED failure) through unit level, optical level (reduced optical output) and performance level (photometric-performance degradation) to operational level (incorrect PAPI indication or degraded approach guidance).
In the alignment chain, foundation settlement leads to structural movement, elevation error, beam-angle deviation, incorrect PAPI indication and approach-guidance degradation. In the optical chain, dust or salt contamination leads to optical-window contamination and reduced optical transmission.
The diagnostic matrix assigns a primary investigation to each topic. PAPI and APAPI unit failures start with complete unit condition, lamp and LED failures with output, driver failure with driver input and output, power-supply failure with the supply path, cable failure with continuity and insulation, and connector failure with connection and contact.
Every failure receives a severity classification, plus operational-impact tagging. The classes are Critical / Safety-Critical (immediate operational or safety risk), Major / Operationally Critical (significant availability impact), Moderate (reduced performance, not yet critical), Minor / Non-Critical (limited or no operational effect), and Degradation / Intermittent / Latent (a developing or hidden fault).
The Troubleshooting Atlas answers “I have a fault now — how do I diagnose and fix it?” The Failure Database answers “this failure happened — what happened, why, what evidence proves it, what was done, and how do we stop it recurring?” Kept strictly separate, then linked end to end, the two form an AGL Failure Intelligence Engine rather than a simple fault list.
A PAPI or APAPI fault can come from lamp/LED degradation, unit settlement, elevation drift or power supply issues — real troubleshooting means understanding glide path geometry and unit construction well enough to find why the beam moved.
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