Which statement best describes the Flight Deck oxygen system?

• A. It has a single mode
• B. It has three modes including Normal, 100%, and Emergency Mode
• C. It uses chemical oxygen
• D. It does not provide oxygen to the crew

Answer: (B)

The flight deck oxygen system is designed to adapt to different flight conditions by offering multiple operating modes. This flexibility ensures pilots have reliable oxygen under normal operation and can quickly ramp up or extend oxygen supply during emergencies.

The best answer reflects that there are three distinct modes: Normal, 100%, and Emergency. Normal mode provides standard oxygen flow during routine operations. The 100% mode delivers full, immediate oxygen flow when rapid or maximum oxygen delivery is required. Emergency mode engages a sustained oxygen supply for extended periods during a loss of cabin pressure or other critical situations, allowing the crew to continue flying and troubleshooting.

This explains why the other possibilities aren’t correct: the system isn’t limited to a single mode, and the flight deck oxygen supply isn’t based on chemical oxygen generation for the crew via this system; it does provide oxygen to the crew.