According to ICAO recommendations, the planning (declared) runway length for an airport is determined considering which fundamental factors?

Introduction / Context:
Runway length must be sufficient for takeoff and landing under limiting conditions. ICAO methodologies adjust a basic length for field elevation, ambient temperature relative to ISA (standard 15°C at sea level), and effective runway gradient, among other local corrections. This question checks recognition of the core factors.

Given Data / Assumptions:

• Baseline length derived for sea level, ISA temperature and zero gradient.
• Corrections applied for elevation, temperature, and slope.

Concept / Approach:
Higher elevation and temperature reduce air density and engine/wing performance, increasing required distance; positive gradients raise rolling resistance, further increasing length. Hence, all listed factors must be considered to obtain practical declared distances (TORA, TODA, ASDA, LDA).

Step-by-Step Solution:
Start with a base length at sea level, 15°C, zero gradient.Apply elevation correction (air density reduction with altitude).Apply temperature correction (deviation from ISA).Apply effective gradient correction (up-slope increases requirement).

Verification / Alternative check:
Design guides and Annex references present these as primary correction factors before other local adjustments (runway surface, wind, obstacles).

Why Other Options Are Wrong:

• Each individual factor is necessary; only “All of the above” captures the complete set.

Common Pitfalls:
Neglecting gradient when it is small but non-zero; ignoring temperature corrections at hot sites which can be critical.

Final Answer:
All of the above