What specific action should a marshaller take if they observe an unsafe condition developing during aircraft movement?

If a marshaller observes an unsafe condition developing during aircraft movement, the specific action they should take is to immediately signal the pilot to stop the aircraft. This signal is a universally recognized hand signal involving raising both arms above the head with hands closed or fists clenched, sometimes accompanied by rapid waving. The immediate halt is crucial to prevent potential collisions, ground damage, or injury to personnel. After signaling the stop, the marshaller must then clearly communicate the nature of the unsafe condition to the pilot, either verbally via radio or using additional standard hand signals if radio communication is not possible or practical. This communication should be concise and informative, enabling the pilot to understand the situation and take appropriate corrective action. The marshaller should also alert other ground personnel to the developing situation to ensure a coordinated response. The priority is always to stop the aircraft's movement as quickly as possible and then communicate the reason for the stop.