AGL FOR CAT II / CAT III AIRPORTS IN INDIA

Precision Approach and Low-Visibility AGL

CAT II and CAT III operations require specialised aerodrome facilities, carefully designed visual aids, dependable power systems and controlled operational procedures. Airfield Ground Lighting (AGL) is one part of this wider precision-approach infrastructure — the exact arrangement is airport- and runway-specific and must be established from the applicable aerodrome documentation, approved design and project requirements.

What CAT II / CAT III Means for AGL

CAT II and CAT III are precision-approach operational categories associated with progressively lower visibility conditions and additional aerodrome facilities. From an AGL engineering perspective, lower-visibility operations can require more extensive and carefully controlled visual guidance systems — considered as part of a wider chain rather than in isolation.

Why AGL Is Critical in CAT II / CAT III Operations

In low visibility, the visual environment available to aircraft crews is reduced. The airfield lighting system therefore has an important role in supporting the guidance functions below — which is why AGL maintenance and serviceability become especially important during Low Visibility Procedures (LVP).

Precision Approach Lighting

Precision approach lighting provides visual guidance in the approach area leading toward the runway. The exact approach lighting configuration is determined by the runway, approach system and approved airport design.

Runway Lighting for CAT II / CAT III

Depending on the runway configuration, the AGL system may include the facilities below. Not every runway will have exactly the same combination of systems — the approved configuration must be checked for the specific aerodrome.

Taxiway Lighting for Low-Visibility Operations

CAT II / CAT III operations can also require enhanced taxiway guidance. Indian AIP documentation provides airport-specific examples of the facilities below.

Taxiway Centreline Lighting

Taxiway centreline lighting provides longitudinal guidance through designated taxi routes, and its role can become particularly important during low-visibility operations. The exact taxiway routes equipped with centreline lighting are airport-specific.

Stop Bar Lighting & Runway Guard Lights

Stop bars are associated with aircraft holding positions and runway-access control. Runway guard lights provide an additional visual indication at runway/taxiway interfaces, and can form part of the low-visibility taxi guidance system alongside stop bars, taxiway centreline lighting and holding-position markings.

AGL Critical Circuits

Not all airfield lighting circuits necessarily have the same operational importance. For CAT II / CAT III applications, airport documentation can identify critical AGL circuits and establish their power, monitoring and serviceability requirements. The specific classification should always be taken from the applicable airport documentation.

AGL Power Supply for CAT II / CAT III

Power supply is a major part of the low-visibility AGL system. The exact architecture, changeover time and backup duration depend on the airport and project.

UPS Support & Automatic DG Takeover

A UPS can provide continuity of supply to critical AGL loads during transfer from the normal power source to standby generation, while a standby Diesel Generator (DG) may provide the longer-duration backup source after loss of commercial power. The exact design parameters must be verified from the airport's approved electrical system.

Power Failure Scenario

A simplified CAT II / CAT III critical-power sequence can be represented as below. The actual switching sequence, backup duration and affected circuits vary by airport.

Hyderabad Airport (VOHS) Example

Current AAI eAIP information for Rajiv Gandhi International Airport, Hyderabad demonstrates one airport-specific CAT II / CAT III AGL arrangement — not a universal design for every Indian airport.

Kolkata Airport (VECC) Example

Current AAI eAIP information for NSCBI Airport, Kolkata shows a different airport-specific arrangement — and should not be copied directly into another airport's design.

CAT II / CAT III AGL Serviceability

Serviceability becomes a critical engineering and operational consideration. The operational consequence of an AGL fault depends on the facility affected, the number and position of failed lights, circuit configuration, RVR / visibility, operational category and airport procedures.

AGL Redundancy & Interleaved Circuits

Critical lighting systems can use multiple circuits or independent power arrangements to reduce the operational effect of a single circuit failure. Some airport systems use interleaved circuits so that lighting points are distributed between circuits — the operational consequence of losing one circuit depends on the actual configuration.

Current Hyderabad AIP information, for example, identifies different circuit arrangements for runway lighting and explains their effect on operational serviceability.

CCR, Transformers & Connectors

The CCR remains a core part of the AGL series-circuit system and should be assessed together with the connected series circuit and critical lighting load. A typical series circuit runs CCR → Primary Cable → Primary Connector → Isolating Transformer → Secondary Connector → Light Fixture, and for critical circuits the complete chain should be maintained and tested as an integrated system.

Control & Monitoring / Relationship with ILS & RVR

Critical AGL systems can require monitoring of CCR status, circuit status, faults, lighting status, power status and control-system status. CAT II / CAT III operations involve more than AGL — the AGL system operates alongside the ILS, RVR and surface movement systems below. The exact interface is airport-specific.

Low Visibility Procedures & Fault Diagnosis

LVP is an operational procedure implemented to support safe airside operations in defined low-visibility conditions. A fault should be traced systematically to distinguish a local fixture failure from a system-level fault. The exact procedure is airport-specific.

Photometry, Electrical Design & Testing / Commissioning

Photometric verification can be especially important for precision visual guidance systems, and alignment matters particularly where the optical output of a fixture is directional — a physically illuminated fixture is not necessarily correctly aligned. CAT II / CAT III design also requires detailed evaluation across series circuit, CCR, power and control disciplines, verified through electrical, functional, photometric, power and final integrated testing.

CAT II / CAT III Compliance Matrix

A useful project document is a dedicated low-visibility AGL compliance matrix. Actual references and acceptance criteria should be populated from the applicable project documentation.

CAT II / CAT III AGL Technical Support

Precision AGL Solutions positions its CAT II / CAT III support around specialised AGL engineering, equipment and technical coordination across the areas below — the answers to a project's key engineering questions should always come from the airport's current documentation.

Frequently Asked Questions

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