Introduction / Context:
Obstacle Limitation Surfaces (OLS) define protected airspace around a runway approach. Understanding how the approach area is laid out on plan, how its dimensions are referenced, and the name of the inclined surface above it is basic to aerodrome design questions.
Given Data / Assumptions:
- The approach area is a plan-view trapezoid (or similar) extending outward from the runway end.
- Its centreline coincides with the runway centreline.
- Approach area plan dimensions are measured on the horizontal plane, while the approach surface above is an inclined imaginary plane.
Concept / Approach:
Plan geometry is defined horizontally; vertical protection is provided by an inclined approach surface with a specified slope (e.g., 1:40 for some instrument runways). “Obstruction clearance surface” may refer to other defined surfaces; it is not simply another name for the approach surface in most usages.
Step-by-Step Solution:
1) The approach area centreline coincides with the runway centreline—true.2) Approach area dimensions are indeed measured on a horizontal reference plane—true.3) The inclined imaginary plane above the approach area is called the approach surface—true.4) “Obstruction clearance surface” and “approach surface” are not the same in general definitions—false.
Verification / Alternative check:
Compare standard OLS diagrams: plan dimensions given in horizontal, with a separate vertical slope defining the approach surface.
Why Other Options Are Wrong:
a/b/c: Omit one of the three correct statements.e: Treats the incorrect Statement 4 as correct; therefore wrong.
Common Pitfalls:
Confusing plan-view measurement plane with the inclined surface; assuming all protective surfaces share the same name.
Final Answer:
Only statements 1, 2, and 3 are correct.
Discussion & Comments