Technical reference
Definitions / Assumptions
Plain-language terms and current V1 assumptions are shown here so calculation context is visible to engineers and reviewers.
Terms
Definitions
- MSL
- Mean sea level elevation datum used for both object top and allowable surface elevations.
- AGL
- Above ground level height measured from the object's base elevation.
- Threshold elevation
- Elevation at the runway threshold or selected runway end used by approach-surface calculations.
- Established airfield elevation
- Military airfield reference elevation used where DoD criteria call for that datum.
- Longitudinal station
- Signed X position along runway centerline, measured from runway midpoint where X = 0.
- Selected runway end
- The runway threshold context used for selected-end approach and clear-zone checks.
- Manual longitudinal offset
- Signed distance from the selected runway end. Negative values move inward toward the runway interior; positive values move outward beyond the selected end.
- Lateral offset
- Signed Y offset from runway centerline. The evaluator uses absolute offset for surface width checks and preserves left/right wording in geometry notes.
- Penetration
- Object top elevation is higher than the allowable surface elevation at the object location.
- Clearance
- Object top elevation is at or below the allowable surface elevation at the object location.
Current release
Assumptions and Scope Limitations
- All calculations compare object top elevation MSL against allowable surface elevation MSL.
- Object stationing is interpreted relative to the selected runway end.
- Manual location input uses negative feet inward from the selected runway end and positive feet outward beyond that end.
- Lat/lon mode computes a local runway bearing and projects the object onto along-track and cross-track axes.
- When both manual and lat/lon inputs are provided, the app reports a warning if the interpreted positions differ by more than 25 ft.
- Approach and clear-zone surfaces are evaluated outward from the selected runway end.
- V1 does not use maps, GIS, terrain models, imagery, runway length, or complete airport layout geometry.
- Rounded horizontal, conical, and outer-horizontal checks are refined by runway-envelope geometry in the evaluator instead of relying on a single selected-end radial fallback.
- Civil Part 77 horizontal-perimeter construction still assumes one active runway/approach category for the evaluated runway and does not yet collect separate mixed-end classifications for the 5,000 ft / 10,000 ft arc-construction rule.
- When a surface is not encoded or does not apply at the input location, the result is NOT_EVALUATED rather than assumed clear.
- Part 77 includes separate heliport criteria under 14 CFR 77.23, but Civil and DoD rotor-wing / heliport paths remain explicitly unsupported in the current release and are not inferred from fixed-wing airport logic.
- FAA AC and UFC / DoD rotor-wing or heliport design criteria require separate rule packs and are not inferred from fixed-wing runway design dependencies in the current release.
- Users remain responsible for verifying inputs, assumptions, criteria selection, and outputs with the authority having jurisdiction before relying on results.
- Rule files are intended for verification and editing before official use.
Implementation
Calculation Methodology Notes
- The evaluator computes object top elevation from ground elevation plus object height unless a direct top-elevation override is supplied.
- Each selected criteria family is evaluated independently so Civil Part 77, DoD Part 77, FAA AC, and UFC outputs remain traceable to their own source logic.
- Surface results report the datum, slope, distance, allowable elevation, and clearance or penetration amount that supported the displayed status.