When should passengers don their oxygen masks if an emergency occurs in flight?

Passengers should don their oxygen masks immediately after the crew puts on their masks during an in-flight emergency. This procedure is crucial for several reasons. First, the crew is trained to respond quickly to emergencies, and their actions indicate the seriousness of the situation. When the crew puts on their masks, it serves as a clear signal for passengers to follow suit, ensuring that everyone can breathe safely in case of sudden cabin decompression or loss of cabin pressure.

Additionally, the crew's leadership in this moment helps to instill calm and order, guiding passengers in a potentially stressful situation. Immediate action is vital because delaying the use of oxygen masks could lead to hypoxia, where a lack of oxygen begins to impair judgment and physical capabilities.

The other options do not align with established safety protocols. Waiting for the captain to regain consciousness, relying solely on the seatbelt sign, or waiting until passengers notice a loss of pressure can lead to delays in securing oxygen, which may jeopardize safety. Therefore, the correct protocol is for passengers to put on their masks right after the crew does, ensuring a swift and organized response to the emergency.