What must a pilot demonstrate to properly apply the 1-2-3 rule during flight planning?

To properly apply the 1-2-3 rule during flight planning, a pilot must demonstrate knowledge of weather conditions. The 1-2-3 rule is a systematic approach that helps pilots assess flight safety by considering the weather at three critical points: the departure airport, the en-route conditions, and the destination. By understanding and evaluating these weather conditions, the pilot can make informed decisions about flight routes, alternate landing options, and any potential impacts on safety and aircraft performance.

A thorough grasp of weather conditions allows a pilot to anticipate challenges such as turbulence, storms, or low visibility, which are crucial for ensuring a safe and efficient flight. Knowledge of these factors can directly affect the planning of the route and the fuel calculations as well, but the foundational aspect is recognizing how weather can influence all segments of the journey. This understanding empowers pilots to make timely adjustments in their planning based on the forecast and current weather observations.