What is the response for a Level 4 threat on an aircraft?

For a Level 4 threat on an aircraft, the response is to ensure that a lockdown subsides only when law enforcement is present. This level of threat indicates a serious situation that requires a coordinated law enforcement response to guarantee the safety of passengers and crew.

In this scenario, the presence of law enforcement is critical as they are trained to handle high-threat situations, including potential hijackings or violent acts. The lockdown is a precautionary measure to protect everyone on board until it is deemed safe to proceed. Therefore, it's necessary for law enforcement officers to assess the situation and establish control before allowing any movement or evacuation, ensuring that all safety protocols are strictly followed.

Other options suggest actions that do not adequately address the severity of a Level 4 threat. Immediate evacuation or notifying ground control may be appropriate in other contexts but do not align with the specific safety measures necessary for a situation classified at this level.