Which oxygen policy applies for passengers bringing their own oxygen on board?

The chosen answer addresses the specific safety regulations and operational policies regarding oxygen use on flights. Under the relevant regulations for Part 135 operations, passengers are generally prohibited from bringing their own oxygen on board except during the critical phases of boarding and deplaning. This is primarily to ensure that all oxygen systems on the aircraft are standardized, functioning properly, and monitored by the cabin crew for safety and compliance reasons.

Allowing passengers to bring their own oxygen at any time could lead to complications, such as different types of oxygen equipment that may not be compatible with the aircraft's environment or safety protocols. It might also create potential hazards in case of emergencies, where predefined oxygen delivery systems are employed to assist all passengers.

While some options suggest different levels of restriction, the correct answer reflects a balanced approach that ensures safety while still accommodating passengers' needs during specific times when they might require supplemental oxygen.