What action must a spotter take during a jump run?

During a jump run, the spotter plays a critical role in ensuring the safety of the jumpers and the flight path. The correct action is to place their head completely outside the aircraft and look straight down. This position allows the spotter to gain a clear and direct view of the ground below, identifying any potential hazards or obstructions that may affect the jumpers. By looking straight down, the spotter can quickly assess the landing area and ensure it is safe for the jumpers to exit the aircraft.

Using side windows or binoculars, as suggested in other options, does not provide the same level of visibility or immediacy required during this crucial moment. Looking out through side windows may inhibit the spotter's ability to see directly below, and relying on binoculars could delay their response times and limit the peripheral awareness needed to ensure safety. Additionally, asking other jumpers to check for safety places the responsibility on others rather than having the spotter fulfill their critical function of monitoring the jump run directly. Thus, positioning oneself to look down directly is essential for effective risk assessment and ensuring a safe jump.