Effective runway length is defined as the distance between which two points relevant to obstacle clearance and the runway surface?

Introduction / Context:
Runway usability depends not only on paved length but also on obstacles in approach and take-off areas. “Effective length” reflects the usable distance considering the obstacle limitation surfaces and declared distances for performance calculations.

Given Data / Assumptions:

• Standard approach obstacle clearance plane and take-off climb requirements.
• Runway surface considered as a reference plane (extended if needed).

Concept / Approach:
Effective runway length accounts for obstacles that may penetrate the approach/take-off surfaces. The controlling end is set by the point where the obstacle clearance line meets the extended runway plane; the distance from that point to the far runway end is the effective length used in planning.

Step-by-Step Solution:
Identify obstructions and draw the obstacle clearance line.Extend the runway surface plane longitudinally to meet this line.Measure the distance from this intersection point to the opposite runway end; this is the effective length.

Verification / Alternative check:
This concept aligns with declared distance methodology (TORA/TODA/ASDA/LDA) where obstacles can reduce usable distances despite full physical pavement being present.

Why Other Options Are Wrong:

• Physical ends or clearway ends ignore obstacle constraints.
• Glide path intersection relates to instrument landing path, not necessarily controlling obstacle geometry for take-off/landing distances.
• Displaced thresholds are consequences, not the definition.

Common Pitfalls:

• Assuming effective length equals physical runway length.
• Neglecting approach obstacles during preliminary planning.

Final Answer:
The intersection of the obstacle clearance line with the extended plane of the runway surface and the other end of the runway