FOD Retention Map-Cleaning Safety Case
Last updated: 2026-05-23
Airside map cleaning must not turn "small, transient, and low to the ground" into "safe to delete." Foreign object debris (FOD) is often exactly that: small, temporary, sparse in LiDAR, and safety critical. A static-map cleaner may remove FOD from the permanent localization map, but it must retain the evidence as a current hazard, alert, or review item.
Safety Claim
Within the validated ODD, the map-cleaning pipeline does not silently erase hazardous FOD-like objects from the operational evidence chain. FOD candidates are either retained in a hazard/review layer, routed to perception/FOD workflow, or explicitly dispositioned by a reviewer.
This claim does not prove the airport is free of FOD. It proves that the cleaning pipeline does not hide FOD evidence it observed.
Do-not-delete hazard rule: map cleaning may exclude transient or movable objects from the permanent static map, but it must not delete them from the operational evidence chain. FOD-like debris, loose tools, straps, hoses, cables, chocks, cones, barrier bases, tow bars, small low obstacles, stationary people, parked or staged GSE, and unknown sparse clusters in route, stand, pedestrian, or FOD-sensitive zones must be exported to hazard, movable_static, or unknown_review, not silently discarded.
Evidence Model
| Evidence item | Minimum content | Why it matters |
|---|---|---|
| Raw sensor evidence | synchronized camera, LiDAR, radar if available, ego pose, calibration, timestamps | supports missed-detection and false-deletion investigation |
| FOD label | object type, size, material, location, confidence, source frame, OpenLABEL ID | distinguishes debris from normal static features |
| Cleaner decision | kept, removed, restored, uncertain, or hazard-layer export | proves FOD was not silently discarded |
| Response link | operator alert, inspection ticket, maintenance closure, or reviewer waiver | connects map hygiene to FOD management |
| Release trace | map tile, route, stand, version, cleaner config, threshold set | supports regression and incident review |
Hazard Matrix
| Failure | Cause | Consequence | Required mitigation |
|---|---|---|---|
| FOD deleted as noise | low height, few points, intensity outlier | false clear in operational corridor | retain rejected low-object candidates for FOD review |
| FOD treated as dynamic clutter | appears in one session only | hazard absent from current-world layer | separate permanent-map deletion from current-hazard reporting |
| FOD hidden by movable-static object | cone, chock, hose, cart, shadow, aircraft gear | missed small object near aircraft | close-range slices and hard-negative/positive pairs |
| FOD merged into ground | wet pavement, low contrast, sparse LiDAR | no alert and no reviewer evidence | camera/radar cross-check and minimum-size validation |
| Reviewer overload | too many nuisance candidates | alerts ignored or bulk-approved | severity tiers, corridor filters, and sampling audits |
| Dataset transfer gap | FOD-A image evidence used for 3D map claim | unsupported map-cleaning acceptance | target-airport placed-object tests |
Test Matrix
| Test slice | Objects | Required result |
|---|---|---|
| Minimum-size placed FOD | metal bolt, rubber, plastic, fabric strap, luggage fragment | candidate is detected or appears in rejected evidence with review tag |
| Low contrast | black rubber on wet asphalt, gray metal on concrete | no silent deletion; confidence recorded |
| Reflective and transparent | foil, polished metal, plastic wrap | retained as unknown/hazard if classification uncertain |
| Near legitimate equipment | chock, cone, barrier foot, tow bar, hose | FOD candidate is not merged into the asset |
| High-clutter stand | aircraft present, carts staged, workers nearby | map cleaner separates permanent deletion from current hazard |
| Hard negative | paint chips, cracks, markings, rubber deposits, drains | false alarm rate reported without relaxing FOD retention |
Metrics And Gates
| Metric | Gate |
|---|---|
| Hazardous-FOD false deletion rate | zero unresolved false deletions in approved test corridor |
| FOD evidence retention | all placed FOD has raw, rejected, kept, or alert evidence trace |
| Do-not-delete hazard retention | zero unresolved hazardous false deletions in approved route, stand, pedestrian, and FOD-sensitive slices |
| Ground-plane localization error | within recovery/inspection tolerance for the site workflow |
| Alert latency | within stop, avoid, or operator-review timing budget |
| False alarm burden | below operational limit without suppressing hazardous candidates |
| Unknown disposition time | within map-publication SLA or tile remains quarantined |
Safety Case Pattern
| Claim element | Practical evidence |
|---|---|
| FOD is treated as a safety hazard | FAA FOD definition, airport FOD program interface, hazard taxonomy |
| Cleaning preserves hazard evidence | rejected-layer audit, OpenLABEL IDs, reviewer disposition |
| Small-object limits are known | FOD-A screening plus target-airport placed-object campaign |
| Operations can act on retained evidence | alert route, inspection ticket, closure status, replayable logs |
| Residual risk is bounded | unresolved classes, minimum detectable size, weather and lighting limits |
Release Checklist
- Lock FOD object definitions, corridor limits, and minimum hazardous size before acceptance runs.
- Preserve raw and rejected points for all low-height candidate objects.
- Report FOD retention separately from dynamic rejection and static preservation.
- Run target-airport hard negatives before lowering alert thresholds.
- Require human disposition for any FOD-like object removed from the candidate static map.
- Attach FOD evidence to the map release or quarantine the affected tile.
- Block publication if a cleaner, semantic filter, or post-processing threshold can suppress small/stationary hazards without preserving rejected evidence and reviewer disposition.
- Route uncovered do-not-delete hazard classes and adverse-airside conditions to a locked local holdout; quarantine the tile or ODD-exclude the condition until target-airside evidence exists.
Sources
- FAA Foreign Object Debris Program: https://www.faa.gov/airports/airport_safety/fod
- FAA AC 150/5210-24A, Airport FOD Management: https://www.faa.gov/airports/resources/advisory_circulars/index.cfm/go/document.current/documentNumber/150_5210-24
- FAA AC 150/5220-24, FOD Detection Equipment: https://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentNumber/150_5220-24
- FAA automated FOD detection system evaluation: https://www.airporttech.tc.faa.gov/Airport-Safety/Airport-Design-Technology/Automated-Foreign-Object-Debris-FOD-Detection-System-Evaluation
- FOD-A paper: https://arxiv.org/abs/2110.03072
- FOD-A repository: https://github.com/FOD-UNOmaha/FOD-data
- ASAM OpenLABEL: https://www.asam.net/standards/detail/openlabel/
- Local context: fod-perception-validation.md