Definition
The maximum distance over which a radio or navigation signal can be received with usable strength and clarity, given the transmitter power, frequency, antenna characteristics, and atmospheric conditions. Despite the misleading name, this term refers to radio signal range, not acoustic sound, and is used in older avionics and radio-range literature to describe how far a station's transmission remains useful to a receiving aircraft.
Plain English
How far away an aircraft can still pick up a clear, usable signal from a ground radio station.
Context Anchor
Seen in discussions of aircraft noise, engine and propeller sound, vibration, and how sound moves through air or aircraft parts.
Derivation
The phrase is a holdover from early radio terminology, when 'sound' was used loosely to mean any audible radio transmission received through headphones. It does not refer to acoustic sound waves traveling through air.
Why Pilots Care
Knowing how sound travels explains sonic boom formation, why aircraft noise reaches the ground differently at altitude, and how temperature inversions affect perceived noise.
Analogy
Sound is like a ripple moving across water. The water does not travel across the whole pond; the disturbance moves through it.
Grounding Statement
If an engine vibrates, that vibration can make pressure changes in the surrounding air, and your ears receive those pressure changes as sound.
Intuition Check
Sound is not a separate object flying through space. It is a vibration being passed through something physical, such as air or metal.
Example Sentence 1
The chart noted the distance the station's sound can travel under normal daytime conditions.
Example Sentence 2
Because sound can travel upward as well as downward, residents miles from the airport still heard the low-flying traffic.