For runway length corrections due to elevation, the length is increased by what percentage for every 300 m rise above mean sea level (MSL)?

Introduction / Context:
Runway length depends on aircraft performance, which is influenced by air density. As elevation increases, density decreases, reducing engine thrust and lift, thereby requiring longer take-off distances. A simple design rule applies a percentage increase per 300 m elevation above MSL.

Given Data / Assumptions:

• Standard day conditions adjusted only for elevation (no temperature or gradient corrections).
• General airport planning guidance for preliminary sizing.

Concept / Approach:
The correction factor acknowledges the density-altitude effect. A commonly adopted planning value is a 7% increase in basic runway length for each 300 m rise in elevation, before applying additional corrections for temperature, gradient, and surface conditions.

Step-by-Step Solution:
Start with basic runway length at sea level.Apply elevation correction: increase = 7% per 300 m.Higher-elevation airports thus require materially longer paved strips for safe operations.

Verification / Alternative check:
Airport design manuals show similar percentage rules for preliminary estimates. Detailed performance charts later refine the requirement using pressure altitude and temperature (ISA deviation).

Why Other Options Are Wrong:

• 3%–6%: underestimate the effect; could lead to insufficient take-off run.
• Other values may apply with temperature and gradient, but the base elevation correction is about 7% per 300 m.

Common Pitfalls:

• Ignoring temperature correction which can be comparable to elevation correction in hot climates.
• Overlooking runway slope and surface effects.

Final Answer:
7%