In airport planning and runway orientation analysis, the most suitable direction for a new runway should align with the dominant wind indicated by the longest line on the wind-rose diagram to maximize headwind coverage and minimize crosswind components.

Introduction:
Runway orientation is a foundational decision in airport engineering. The objective is to align the runway so that aircraft take off and land as nearly as possible into the prevailing winds. The wind-rose diagram summarizes frequency and direction of winds; its longest spoke highlights the most frequent wind direction, which is typically the preferred alignment to reduce crosswind components and improve operational reliability.

Given Data / Assumptions:

• A wind-rose diagram is available for the site with directional frequencies.
• Aircraft performance is better with headwind components and is limited by crosswind components.
• Standard planning seeks maximum wind coverage, often targeting 95% availability within allowable crosswind limits.

Concept / Approach:

Select the runway alignment that maximizes headwind exposure while keeping crosswinds within aircraft limits. The longest wind-rose line corresponds to the direction with the highest frequency of winds, thus offering the best alignment for routine operations and reduced crosswind closures.

Step-by-Step Solution:

Verification / Alternative check:

Cross-validate with wind coverage calculations. Aligning the runway along secondary directions (shorter spokes) generally decreases coverage and increases crosswind exceedances.

Why Other Options Are Wrong:

• Shortest line: Represents infrequent winds; poor coverage.
• Line 'clear' of diagram: No statistical support; not data-driven.
• None of these: Incorrect because there is a clear best practice.
• Median line regardless of length: Ignores frequency; can increase crosswind exceedances.

Common Pitfalls:

• Confusing mean wind direction with most frequent direction.
• Ignoring seasonal or diurnal wind patterns without adequate data duration.

Final Answer:

longest line on wind rose diagram