Question

The best direction of a runway is along the direction of

• A. Longest line on wind rose diagram
• B. Shortest line on the wind rose diagram
• C. Line clear of wind rose diagram
• D. Independent of the wind direction

Hint:

The primary objective of runway orientation is to ensure maximum usability and safety by minimizing the occurrence of strong crosswinds. A wind rose diagram is an essential tool for this, with the longest petal indicating the most favorable direction for runway alignment. This maximizes the time aircraft can operate safely with a headwind.

Answer 1

The Correct Option is A

Step 1: Understand the purpose of a wind rose diagram in airport design.
A wind rose diagram is a graphical representation of wind speed and direction data for a specific location over a period (usually several years). It shows the percentage of time wind blows from various directions and at different speeds. For airport design, particularly runway orientation, wind data is crucial to ensure safe and efficient aircraft operations.
Step 2: Relate wind direction to runway orientation for optimal safety and efficiency.
Aircraft generally prefer to take off and land into the wind (headwind) because it:

• Increases lift at lower ground speeds, allowing for shorter take-off and landing distances.
• Improves control and stability, especially during landing and take-off.

Crosswinds, on the other hand, can create challenging conditions, potentially causing an aircraft to drift sideways, making take-off and landing difficult or unsafe if they exceed certain limits (crosswind component limit).
Step 3: Analyze how the wind rose diagram helps determine the best runway direction.
The objective of runway orientation is to provide a runway or set of runways such that aircraft can take off or land with a headwind for the maximum possible time. This is achieved by aligning the runway with the predominant wind direction.

• Wind Rose Diagram Interpretation: On a wind rose diagram, the length of a line (or petal) in a particular direction indicates the percentage of time the wind blows from that direction. Therefore, the longest line represents the direction from which the wind blows most frequently and/or with higher intensity.
• "Wind Coverage": The runway system is designed to provide "wind coverage," which is the percentage of time that the crosswind component on a runway is within the acceptable limits for the majority of aircraft using the airport. For most large aircraft, the maximum permissible crosswind component is around 20 knots. The goal is to achieve a wind coverage of at least 95% for the total operating time.
• Longest Line Implication: Orienting the runway along the direction of the longest line (most frequent wind direction) on the wind rose diagram ensures that the runway experiences headwind conditions for the greatest percentage of time, thereby maximizing the usability of the runway and minimizing exposure to excessive crosswinds.

Step 4: Evaluate the given options.

• (1) Longest line on wind rose diagram: This is the correct principle. Aligning the runway with the most frequent wind direction maximizes headwind operation.
• (2) Shortest line on the wind rose diagram: This would mean orienting the runway along a direction where the wind rarely blows, which is inefficient and unsafe.
• (3) Line clear of wind rose diagram: This statement is ambiguous and does not represent a valid design principle.
• (4) Independent of the wind direction: This is incorrect. Wind direction is a primary consideration in runway design due to its critical impact on aircraft operations and safety.

Step 5: Select the correct option.
The best direction of a runway is along the direction of the longest line on the wind rose diagram, as this corresponds to the predominant wind direction. $$\boxed{\text{Longest line on wind rose diagram}}$$