Which signaling is used when additional personnel are needed for a safe departure?

The choice of signaling that indicates additional personnel are needed for a safe departure is the request for a wingwalker. A wingwalker is a ground crew member responsible for ensuring the safe movement of the aircraft, especially during taxiing. Their primary role is to monitor the surroundings of the aircraft to prevent collisions or other accidents as the aircraft is in motion. When a wingwalker is requested, it signals the need for extra attention and assistance in navigating safely, particularly around obstacles or other aircraft, which is crucial for maintaining safety protocols.

Other choices relate to different aspects of aircraft preparation and movement. Signaling "ready to depart or ready to tow" indicates that the aircraft is prepared for its next phase but does not specifically request additional personnel. The "remove chocks" signal pertains to the action of removing wheel chocks that prevent the aircraft from rolling but doesn't imply a need for additional ground crew. The "want air supply unit" request indicates the need for an external air supply for starting engines or for cabin air but also does not call for extra personnel. Thus, the request for a wingwalker is the appropriate signal for needing more manpower to ensure safety during departure.