When does the amount of available cabin oxygen decrease?

When does the amount of available cabin oxygen decrease?

• A. At lower altitudes
• B. At higher altitudes; aircraft must be pressurized for sufficient supply
• C. During descent
• D. After landing

Answer: (B)

As you rise in altitude, the amount of oxygen available in a sealed cabin depends on cabin pressure. The air inside is kept at a uniform mixture, but the partial pressure of oxygen drops as the outside atmosphere gets thinner. To maintain a breathable environment, the aircraft’s environmental control system pressurizes the cabin to a lower-altitude equivalent (often around 6,000–8,000 feet). This pressurization keeps the oxygen partial pressure high enough for normal respiration. So, at higher true altitudes, the cabin would have less usable oxygen per breath unless it’s pressurized to that safer level. Descent or landing lowers the cabin altitude, increasing oxygen availability, while the denser air at lower altitudes already provides more breathable oxygen.

As you rise in altitude, the amount of oxygen available in a sealed cabin depends on cabin pressure. The air inside is kept at a uniform mixture, but the partial pressure of oxygen drops as the outside atmosphere gets thinner. To maintain a breathable environment, the aircraft’s environmental control system pressurizes the cabin to a lower-altitude equivalent (often around 6,000–8,000 feet). This pressurization keeps the oxygen partial pressure high enough for normal respiration. So, at higher true altitudes, the cabin would have less usable oxygen per breath unless it’s pressurized to that safer level. Descent or landing lowers the cabin altitude, increasing oxygen availability, while the denser air at lower altitudes already provides more breathable oxygen.