What term encompasses both ADF and NDB equipment for aircraft navigation?

The correct answer is the term that best includes both ADF (Automatic Direction Finder) and NDB (Non-Directional Beacon) equipment used in aircraft navigation systems. ADF is a type of radio navigation system that uses the signals from NDBs, which transmit non-directional signals, to determine the aircraft’s direction relative to the beacon.

This terminology focuses specifically on the components and functionality related to the reception and interpretation of these radio signals, which assist pilots in determining their position and navigating safely. By acknowledging ADF and NDB within a dedicated system, it emphasizes the relationship and dependency between the two.

The other choices do not accurately capture the specific nature of the equipment in question. While "guidance system" and "control system" denote broader categories of avionics that may involve navigation tasks, they do not specifically highlight the radio navigation elements represented by ADF and NDB. "Navigation system" could loosely fit, but it is a more general term that encompasses many types of navigational aids beyond just ADF and NDB. Thus, the most accurate and specific choice that directly refers to the relationship between the two pieces of equipment is indeed the ADF system.