Maximum altitude for single-pack operation?

• A. 28,000 ft
• B. 31,000 ft
• C. 34,000 ft
• D. 37,000 ft

Answer: (B)

The concept being tested is how much environmental control capacity is available when only one air conditioning pack is used. In aircraft that normally use two packs, both share the workload to condition cabin air and help with pressurization. If one pack is shut down or fails, the remaining pack has to handle the full load. As you climb, air becomes thinner and the demand on the system to maintain comfortable cabin temperature and proper cabin pressure increases. At higher altitudes, a single pack simply doesn’t have enough capacity to meet that demand, so operation is limited to a lower ceiling. For this configuration, that limit is 31,000 feet, so you can fly with one pack up to FL310 but not higher.