As per International Civil Aviation Organization (ICAO) conventions on aerodrome data, runway lengths are categorized using which coding basis?

Introduction / Context:
ICAO uses an Aerodrome Reference Code comprising two elements: a numeric code (1–4) primarily tied to runway length and a letter code (A–F) tied to aircraft dimensions. Exams often simplify this to ask which general type of coding (letters or numbers) is associated with runway length categorization.

Given Data / Assumptions:

• The question isolates “runway lengths” rather than aircraft size.
• Hence, it targets the numeric element of the ICAO code set.

Concept / Approach:
Runway length categories map to numeric codes in the ICAO scheme. In classical MCQ phrasing, this is summarized as using the “first seven natural numbers,” intending to emphasize numbers rather than letters (even though practical ICAO code numbers are 1–4). The correct categorical answer, therefore, is the one pointing to numbers, not letters.

Step-by-Step Solution:
Identify which part of the ICAO code relates to runway length: numeric.Among options, only the “natural numbers” choice reflects numeric coding.Select “First seven natural numbers.”

Verification / Alternative check:
ICAO Annex references clearly separate the numeric runway-length code from the letter aircraft-size code; thus a numeric choice is conceptually correct in such MCQs.

Why Other Options Are Wrong:

• Alphabet options refer to the aircraft size (code letters), not the runway length category.

Common Pitfalls:
Assuming letters apply to runway length; mixing up code elements.

Final Answer:
First seven natural numbers