AGL Frangible Coupling for Elevated Airfield Equipment

What It Is

Frangible couplings provide a controlled mounting interface for selected elevated airfield lights and visual-aid equipment while supporting the frangibility requirements associated with airfield installations.

They form a defined mechanical connection between compatible equipment and its mounting support, with the configuration selected for the fixture, mounting arrangement and applicable project requirements.

Key Features

• Designed for compatible elevated airfield equipment
• Defined fixture-to-support mounting interface
• Supports frangibility considerations
• Project-specific mounting interfaces available
• Integrates with compatible mounting stems and support assemblies
• Compact mechanical connection
• Selection by fixture type, mounting geometry and mechanical requirements
• Suitable for new installations and selected replacements

Role

The coupling connects the supported fixture to its mounting structure. Correct selection keeps it mechanically compatible with the equipment while maintaining the intended frangible characteristics of the assembly.

Principle

Select the coupling as part of the complete mounting arrangement, not as a generic threaded adaptor.

Compatibility Depends On

• Equipment mounting interface and thread configuration
• Fixture weight and mounting geometry
• Applicable mechanical requirements

Action

Confirm the fixture type and existing or proposed support arrangement so the correct coupling configuration can be selected.

Use

May form part of compatible PAPI mounting arrangements where an elevated support interface is required. Coordinate with the PAPI mounting stand, support geometry and equipment manufacturer's requirements.

Principle

The coupling arrangement must not interfere with required aiming, adjustment or alignment of the equipment.

FAA AC 150/5345-28H requires PAPI mounting legs to use frangible couplings per FAA Drawing C-6046 or an equivalent that passes its frangibility test, so confirm the coupling is the one approved for the PAPI model. After replacing a coupling or disturbing a PAPI unit, re-aim it and verify the angle settings as required by the PAPI manufacturer and the airport's commissioning and flight-check procedure.

Role

With a mounting stem, the coupling is the mechanical transition between the elevated fixture and the supporting stem.

Verification

Verify thread and dimensional compatibility before installation. The assembly should connect the fixture securely while keeping the intended frangible design characteristics.

Principle

Frangible performance depends on coupling design, material, geometry, installation configuration and connected equipment. Establish breaking characteristics from the applicable product configuration and project requirements, not from thread size alone.

Caution

Do not modify, machine or alter the coupling without authorisation where this could affect its intended mechanical or frangible behaviour.

Assembly-Level Approval

Frangibility is demonstrated for the complete fixture, coupling and support assembly, not for the coupling alone. FAA certification, for example, lists specific fixture and mounting-method combinations as approved, so a coupling that matches the thread may still fall outside the certified assembly.

Confirm the coupling is approved for the exact fixture and support. Do not mix makes without written confirmation from the equipment manufacturer.

Break Point and Cables

The frangible section is the intended break point and must sit at the height required by the governing standard. Keep the secondary cable and connector free to separate: do not let rigid conduit, cable clamps or fixings bridge or restrain the break point.

Installation Should Confirm

• Correct coupling type for the fixture
• Correct mounting thread or interface
• Compatibility with the mounting stem or support
• Correct fixture orientation
• Secure mechanical engagement, tightened only to the manufacturer's specified torque (over-tightening can change breakaway behaviour)
• No damage or modification to the frangible section
• Adequate clearance around the installed equipment

Principle

Install per the applicable equipment and project installation requirements.

Replace a coupling after any impact or bending, even if it looks intact, because hidden damage can change its break load.

Use

For selected replacement and refurbishment projects where an existing elevated fixture or mounting arrangement needs a compatible replacement interface.

Check Before Ordering

• Fixture type
• Thread/interface
• Support arrangement
• Required frangible characteristics

Inspect For

• Mechanical damage, corrosion or deterioration
• Loose connections, thread or interface damage
• Signs of unauthorised modification
• Distortion or damage to the frangible section

Action

Assess and replace any coupling showing damage that could affect its intended mechanical or frangible performance.

Principle

Follow applicable airfield lighting, visual-aid, equipment and project requirements. Required frangibility characteristics depend on the specific application and installation configuration.

Review

Review the fixture manufacturer, mounting arrangement and applicable aviation authority requirements when confirming final coupling selection.