Final answer:
The letters VHF/DF in the Airport/Facility Directory signify that an airport is equipped with both Very High Frequency and Direction Finding radio systems, enabling communication and navigational assistance to aircraft.
Step-by-step explanation:
The letters VHF/DF appearing in the Airport/Facility Directory for a certain airport indicate that the airport has both VHF and DF radio systems. VHF stands for Very High Frequency, which is a type of short-range radio communication used in aircraft. DF stands for Direction Finding, a type of radio navigation used by aircraft to determine their position relative to a non-moving radio source.
When both are listed together, it suggests that the airport is equipped to communicate with aircraft using VHF radio and help them determine their direction via DF equipment.