What does the black arrow mark on an airport diagram indicate?

The black arrow mark on an airport diagram indicates the highest obstacle on an Instrument Approach Procedure (IAP), Standard Instrument Departure (SID), or Standard Terminal Arrival Route (STAR). This is critical information for pilots as it helps them understand potential hazards in the airspace associated with the approaches to and departures from an airport. By highlighting the highest obstacle, the diagram assists in ensuring safe vertical separation and aids in the planning of flight maneuvers around these obstacles.

The other options pertain to different aspects of airport operations. For instance, fuel service locations and runways in use are provided on airport diagrams but are not indicated by a black arrow. Similarly, while navigation stations are important for flight guidance, they are represented through different symbols on the diagram, not by a black arrow. Therefore, recognizing the significance of the black arrow is essential for maintaining safety during flight operations near airports.