Overhead and Internal System FOD Sources

Standard FOD walks train people to look down. A complete program trains them to look up and to think about what is inside the systems they maintain. The guide covers this under FOD from above and within systems, and it identifies FOD sources in three dimensions: surface, overhead and internal. This article walks through the overhead and internal sides, plus the aircraft, ground support equipment and vehicles that both suffer and create debris.

Overhead FOD Sources

Overhead sources produce debris that falls on aircraft, equipment and people, and they are invisible to a ground-only inspection. The guide groups them as follows.

Hangar and building overhead:

• Loose or damaged ceiling tiles, insulation and light covers.
• HVAC ductwork: loose fasteners, rust particles, condensation drips and filter debris.
• Structural steel: rust scale, loose bolts, flaking paint and weld spatter left from original construction or modifications.
• Fire suppression sprinkler heads and piping: corrosion, loose fittings and accidental discharge residue.
• Overhead doors: track wear debris, loose hardware and lubricant drips.

Crane and hoist systems: bridge and trolley wear that generates metal particles and lubricant drips, loose or frayed cable shedding wire fragments, hooks, shackles and lifting attachments not secured when idle, and loads that shed dirt or loose packaging during a lift.

Mezzanines, catwalks and elevated walkways: items kicked off edges (tools, hardware, personal items), debris falling through grating or gaps in decking, and accumulated dust and debris on horizontal surfaces that becomes airborne or falls when disturbed.

Controls for Overhead Sources

• Include overhead inspection points in facility audit checklists, such as our FOD audit checklist for aviation and aerospace facilities.
• During FOD walks, train personnel to look up periodically, particularly when passing under overhead structures.
• Do not park aircraft or critical equipment under known overhead debris risks.
• Schedule overhead cleaning and inspection before debris accumulates to the point of falling.
• After any overhead maintenance work such as light replacement, HVAC service or structural repair, inspect the area below for debris the work generated.

Internal System Debris

Debris generated or trapped inside aircraft, engines and equipment is especially dangerous because routine visual inspection cannot see it. The guide lists these categories of internal FOD sources.

• Engine internals: tools, rags, plugs, caps and hardware left during maintenance, broken tool fragments, eroded or liberated internal material such as blade coatings, seal material and bearing particles, ice shedding from internal surfaces during start or power changes, and debris drawn in through the intake during ground operation without engine covers.
• Ducting and plumbing: debris in air conditioning and bleed air ducts introduced during maintenance or through open connections, fuel system contaminants (particulates from fuel trucks or tank corrosion, sealant fragments, and debris introduced through open ports during fueling), hydraulic system seal fragments and wear particles, and pitot-static blockage from insects, water, ice or maintenance contaminants.
• Avionics, electrical and confined spaces: wire clippings, connector debris and terminal fragments, loose hardware in avionics bays, racks and junction boxes, debris trapped behind panels, under floorboards and in bilge areas that can migrate to critical systems, and tooling left in confined spaces, such as a socket left in a wing spar or empennage cavity.

Aircraft, Ground Support Equipment and Vehicles as FOD Sources

Every aircraft, vehicle and piece of ground support equipment is both a potential victim and a potential source. Aircraft shed fasteners, wear particles and sealant through vibration and normal operation, leak fluids that attract and trap debris, shed tire wear or tread pieces and ice after a cold soak, and carry items left on the exterior by people, such as covers, pins, caps, checklists and tools. Ground support equipment adds loose hardware, fluid leaks from poorly maintained units, tire debris from running on deteriorated pavement, and items falling from unsecured loads or operators. Personnel vehicles track debris into controlled areas on tires and undercarriage, lose parts or cargo, and shed rust, trim and exhaust components as they age.

The guide recommends these control measures:

• Inspect ground support equipment for FOD-generating conditions during routine maintenance.
• Designate vehicle routes and parking areas to minimize debris migration, and clean equipment before it enters FOD Critical or Control areas.
• Train vehicle operators to inspect their vehicles for loose items before entering controlled areas.
• Report aircraft-shed debris as a FOD finding with the aircraft identified as the source. That data can point to specific aircraft with recurring shedding problems that need a maintenance investigation.

Vertical and Internal Inspection in Practice

A complete inspection considers surface, overhead and internal dimensions, and the guide sets different expectations for walks, maintenance and audits.

• During walks: scan from overhead down to the surface in a systematic sweep, and pause at known overhead risks such as under cranes, below mezzanines and near overhead doors to look up deliberately.
• During maintenance: before closing any access panel, door or cover, inspect the cavity with a flashlight or borescope as a last-chance inspection. After any task, conduct a tool count and consumable count before closure. For engine, flight control, fuel system and hydraulic system work, the governing task procedure may call for an independent FOD inspection by a second qualified person before closure. If no procedure covers the task, the guide suggests setting this up as a local control for selected critical tasks, with the verifier’s qualification and authority defined.
• During audits and facility inspections: include overhead and internal inspection points on the checklist, sample cavities and confined spaces for accumulated debris (particularly ones not opened for long periods), and inspect overhead structures for storm damage after severe weather.

Good containment habits back these controls up. Personal FOD bags and lidded FOD cans at the work position keep clippings, caps and hardware from ending up in the cavity you are about to close, and FOD signs near known overhead risks remind people to look up. Related reading: environmental and wildlife FOD for storm and ice hazards, and the FOD return-to-service checklist for closing out maintenance.

Get the Full Chapter and Forms

The complete guide covers overhead, internal and equipment sources with the audit and walk forms that support them. Request the free 216-page guide to get the full text and toolkit.