In airport Obstacle Limitation Surfaces (OLS), the conical surface rises outward at what slope?

Introduction / Context:
The conical surface is part of the Obstacle Limitation Surfaces (OLS) that protect airspace around an aerodrome. It extends above and around the horizontal surface, rising gently outward to limit obstacle heights progressively with distance.

Given Data / Assumptions:

• Standard ICAO-aligned values commonly use a conical surface slope of 1:20 (vertical:horizontal).
• Other surfaces (approach, transitional) may have different slopes.

Concept / Approach:
The conical surface provides a gradual height increase limit to ensure obstacle clearance in the vicinity of the aerodrome while accommodating practical development.

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

Common Pitfalls:

Final Answer: