Clear Path

Definitions / Assumptions

Plain-language terms and current V1 assumptions are shown here so calculation context is visible to engineers and reviewers.

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 reference end

  The runway end used for selected-end approach and clear-zone checks. The positive-X end is at runway length / 2 and the negative-X end is at -runway length / 2.

• 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.

Assumptions and Scope Limitations

• All calculations compare object top elevation MSL against allowable surface elevation MSL.
• Object stationing uses runway midpoint as X = 0 and a selected positive-X or negative-X reference 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 reference end.
• V1 does not use maps, GIS, terrain models, imagery, runway length, or complete airport layout geometry.
• Horizontal and conical checks use radial distance from the selected runway end as a simplified input.
• When a surface is not encoded or does not apply at the input location, the result is NOT_EVALUATED rather than assumed clear.
• Rule files are intended for verification and editing before official use.

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 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.