AGL Mounting Stem for Elevated Airfield Lights

A mounting stem provides the mechanical support interface between an airfield light and its base or mounting assembly. It establishes the required fixture elevation and mounting position, and gives a compatible connection between the light fixture, base, extension components or frangible coupling.

They are used for elevated airfield light fixtures on deep or shallow bases, in fixed-height or adjustable-height mounting arrangements, in installations needing an extension between the base and the light, in replacement and refurbishment projects and in arrangements that include a frangible coupling.

Stem length determines the installed elevation of the fixture. Select it from the lighting application, mounting arrangement and finished installation level. Where an extension stem is required, assess the complete assembly, and the resulting fixture height and mechanical configuration must meet project requirements.

The upper interface should match the fixture or intermediate coupling, and the lower interface should match the selected base or support arrangement. Correct interface selection is essential for mechanical compatibility and the intended fixture position. Confirm the base and stem interfaces together before procurement to avoid thread, diameter or dimensional incompatibility.

Stems can be configured for use with compatible deep bases, shallow bases, base plates, extension stems, frangible couplings and other approved mounting assemblies.

Where the installation requires a frangible mounting arrangement, the stem can be coordinated with a compatible frangible coupling, which provides the transition between the supporting stem and the elevated fixture. Treat the coupling, stem and fixture as one complete mounting assembly when checking compatibility and installation requirements.

Elevated lights on the movement area must be frangible and low enough to clear aircraft. The frangible point is normally the coupling, so the stem must stay rigid and not become the weak point, and its length should not raise the fixture above the permitted height.

Material depends on the mechanical requirements and environmental conditions of the installation. Protective coatings or finishes may be specified where additional resistance to corrosion and environmental exposure is needed, and the finish should be compatible with the surrounding airfield environment and the other components in the assembly.

Confirm the correct stem length, diameter and mounting interface, compatibility with the selected base and with the fixture or frangible coupling, the correct finished fixture elevation, secure mechanical engagement, correct orientation of the fixture and an appropriate tightening and installation procedure. Install the stem without unauthorised modification that could affect its mechanical performance or compatibility.

Assess the existing fixture, base, thread or interface, installed height and surrounding mounting components. Where the original configuration is being modified, confirm compatibility between the replacement stem and all connected components before installation.

Inspect for corrosion or coating deterioration, mechanical damage, loose or damaged connections, thread or interface damage, misalignment and evidence of unauthorised modification, and replace any component showing damage that could affect fixture support or alignment. References include ICAO Annex 14 Vol. I Chapter 5, ICAO Doc 9157 Part 6 on frangibility, FAA AC 150/5220-23A on frangible connections, FAA AC 150/5345-42K and FAA AC 150/5340-30J. Certified fixtures and their mounting parts follow the manufacturer’s certified assembly.