What is the formula for calculating the VHF range in aviation?

The formula for calculating the VHF range in aviation is correctly represented by the first option: d = 1.23 * (√h1 + √h2). This formula provides a way to estimate the line-of-sight distance (d) between two antennas based on their respective heights (h1 and h2) above sea level.

The factor of 1.23 in the formula is derived from the properties of radio wave propagation, particularly in the VHF band. The square root of the heights is used because the line-of-sight distance for radio waves is proportional to the square root of the antenna heights, which accounts for the curvature of the Earth and the height at which the receiver and transmitter are located.

This relationship allows for a simplified calculation that provides a quick approximation of communication range, which is crucial for ensuring reliable radio transmissions in aviation operations. In practical terms, this means that as the heights of the antennas increase, the radio range also increases, but at a rate that follows the square root of their heights, rather than being linear or exponential.