Who instructs jumpers to approach the aircraft?

The correct choice is the Jumpmaster. The Jumpmaster is responsible for overseeing the jump operations, ensuring that all procedures are followed for the safety and efficiency of the jump. Part of their duties includes instructing jumpers on when to approach the aircraft, ensuring that they are ready and prepared for the jump. This involves conducting a comprehensive safety brief and coordinating the jump sequence to maintain optimal safety protocols.

While the Crew Chief, Safety Officer, and Flight Engineer have distinct and crucial roles during the aircraft operations and jump procedures, their responsibilities do not typically include the direct instruction of jumpers as they approach the aircraft. The Crew Chief's role focuses more on the aircraft's operational aspects and not specifically on jump operations. The Safety Officer assesses the overall safety of the operation, while the Flight Engineer manages the aircraft's systems and performance. Thus, the Jumpmaster's responsibilities specifically align with the instruction and management of jumpers before taking off.