What is a common scenario for using portable oxygen bottles on board?

Portable oxygen bottles are primarily utilized in scenarios where there is a need to address passenger incapacitation. This can occur due to various reasons, such as a medical emergency or a significant drop in cabin pressure, which affects oxygen availability. Oxygen bottles provide supplemental oxygen to assist those who may not be getting enough air, ensuring their safety and comfort until further medical assistance can be provided.

In contrast, other scenarios such as turbulence, serving food, or preparing for an emergency landing may not directly necessitate the immediate use of portable oxygen. Turbulence typically does not require extra oxygen, and while food service involves safety protocols, it generally does not call for additional oxygen supplies. Preparing for an emergency landing may involve other safety measures but does not specifically warrant the use of portable oxygen unless there is a specific need identified at that moment. Hence, the most suitable and common scenario for deploying portable oxygen bottles remains passenger incapacitation.