Under what wind condition should a runway aligned with the wind be used?

Using a runway aligned with the wind is ideal for enhancing aircraft performance during takeoff and landing, particularly when the wind is blowing at a speed of 5 knots or more. This condition provides a headwind component that can help to reduce the takeoff distance required, as well as improve the climb rate during takeoff. Similarly, during landing, having a headwind allows for better control and a shorter landing roll.

While higher wind speeds may also benefit performance, the emphasis is on the ability to efficiently and safely operate under typical conditions. A headwind, even at lower speeds like 5 knots, improves the performance margin and allows pilots to make more effective use of the aircraft's capabilities.