Obstacle limitation surfaces: for a Class A airport, what is the difference in reduced levels between the lower and higher edges of the conical surface (i.e., the conical height)?

Introduction / Context:
Obstacle Limitation Surfaces (OLS) protect aircraft flight paths around aerodromes. The conical surface is an inclined shell that extends upward and outward from the edge of the inner horizontal surface. Its height (difference between lower and higher edges) is standardized to ensure obstacle control in the surrounding airspace.

Given Data / Assumptions:

• Airport classification: Class A (per conventional Indian/ICAO-influenced practice).
• We are asked for the vertical difference (conical height), not radius or slope length.

Concept / Approach:
For Class A airports, the conical surface commonly rises at a gentle slope (e.g., 5%) up to a fixed vertical height of about 100 m above the inner horizontal surface. This provides a protected volume to accommodate climb-out and circuit operations while controlling tall structures in the vicinity.

Step-by-Step Solution:
Identify the specific OLS: conical surface.Recall the standardized conical height: approximately 100 m for Class A layouts.Select 100 m as the correct difference in reduced levels.

Verification / Alternative check:
Airfield zoning plans depict the conical surface as annular frustums around the airfield reference point; the height annotation is typically 100 m with a corresponding ground-projection width set by the slope.

Why Other Options Are Wrong:

• 25–75 m: too small to provide the standard protective volume for Class A operations.

Common Pitfalls:

• Confusing the conical height with the inner horizontal surface elevation itself.

Final Answer:
100 m.