What is the usable distance of VKS and BLE NDB's?

The correct answer regarding the usable distance of VKS and BLE NDBs (Non-Directional Beacons) is based on their operational characteristics and typical performance. For VKS and BLE NDBs, the usable distance is generally around 25 miles under standard conditions. This range is determined by factors such as the power output of the transmitter, receiver sensitivity, terrain, and atmospheric conditions, which can all influence the effective range of radio signals.

The choice of 25 miles reflects an established understanding within aviation and navigation standards regarding the distance at which these types of NDBs typically retain reliable signal quality for aircraft navigation. Factors such as signal quality, interference, and environmental conditions can further affect the range, but 25 miles is a standard distance recognized in operational guidelines.

The other options provided suggest distances that do not align with typical expectations and documented performance metrics for VKS and BLE NDBs, as the typical operational distance is recognized to be within the 20-30 mile range, with 25 miles being a commonly accepted figure.