What is the correct way to issue a crossing clearance over an active runway to a taxiing aircraft?

• A. <Callsign>, cross Runway <number> when safe, proceed as directed.
• B. <Callsign>, cross Runway <number> after ensuring clearance from the Runway in use.
• C. <Callsign>, cross Runway <number> when safe, proceed as directed.
• D. <Callsign>, cross Runway <number> at the end of operations only.

Answer: (C)

Crossing an active runway requires a clear, safety-focused instruction that tells the pilot when to begin the crossing and what to do after. Saying “cross Runway number when safe, proceed as directed” gives two essential pieces: the crossing can only start when the controller has confirmed it is safe, and after crossing the aircraft should follow the controller’s directions for the remainder of the taxi route. This phrasing cleanly separates the safety condition from the subsequent instructions, which helps prevent confusion or delays.

Phrasing like waiting for clearance from the runway in use adds an extra, unclear requirement that isn’t part of standard crossing clearances and can create ambiguity. And instructing to cross only at the end of operations is inappropriate because crossings can occur during active operations and must be coordinated in real time.