What is the correct procedure to signal the flight crew if a potential hazard is observed near the aircraft while taxiing?

If a potential hazard is observed near the aircraft while taxiing, the correct procedure to signal the flight crew involves a combination of visual signals and, if possible, radio communication. The primary visual signal is the emergency stop signal. This is executed by extending both arms above the head and crossing the wands or illuminated batons (if used) to form a distinct "X" shape. This signal immediately conveys to the flight crew that they must stop the aircraft as quickly and safely as possible. The marshaller must maintain this signal until the aircraft comes to a complete stop. Simultaneously, if radio communication is available, the marshaller should immediately contact the flight crew on the designated ground frequency and clearly state: "STOP, STOP, STOP," followed by a brief description of the hazard. For example, "STOP, STOP, STOP, object on taxiway ahead." The radio message reinforces the visual signal and provides the flight crew with additional information about the nature of the hazard. If the hazard is on the aircraft's left side, the marshaller should also use their left arm to point towards the hazard. Conversely, if the hazard is on the right side, the marshaller should use their right arm to point towards the hazard. This helps the flight crew to quickly locate the hazard. The marshaller should remain in a visible position and continue to monitor the situation until the hazard has been resolved and it is safe for the aircraft to resume taxiing. After the aircraft has stopped and the hazard has been addressed, the marshaller should use the appropriate taxiing signals to guide the aircraft around the hazard or back to the correct taxiway. The emergency stop signal should only be used when there is an immediate and significant safety threat to the aircraft or personnel.