What action is required when four or more chimes are heard?

When four or more chimes are heard, it signals an urgent situation that requires immediate attention, and the correct action is to evacuate the aircraft. This alert typically indicates a critical emergency, such as a rapid decompression, fire, or other situations that pose an immediate risk to the safety of the passengers and crew.

Evacuating the aircraft is essential to ensure everyone's safety and to respond to the emergency effectively. It allows for the swift movement of passengers away from potential hazards and enables the crew to manage the situation according to emergency procedures. The urgency of responding to this signal cannot be overstated, as lives may depend on the timely and efficient action of the crew.

In contrast, actions such as preparing to serve meals, changing cabin pressure, or reporting to the captain do not address the imminent danger indicated by the chimes. These alternatives would unnecessarily delay a critical response to a potential emergency situation. Thus, the focus must be on evacuation.