CFR Part 121 requires that there is ____ POB onboard for each crewmember.

• A. 0
• B. 1
• C. 2
• D. 3

Answer: (B)

In this context, having a portable oxygen bottle (POB) ready for use by each crewmember is essential for immediate, independent access to oxygen during in-flight emergencies such as depressurization or medical events. The requirement means the aircraft must carry one POB for every crewmember on board, so no crew member is left without oxygen if another bottle is in use or needed elsewhere. This is the minimal, practical standard because it ensures that any crewmember can rapidly obtain oxygen without waiting or sharing, which supports the ability to perform duties and respond effectively under stress. Having fewer bottles would compromise safety, while more than one per crewmember isn’t required by regulation and would add unnecessary weight.