What is the maximum altitude for single A/C pack operation?

• A. 28,000 ft
• B. 33,000 ft
• C. 31,000 ft
• D. 35,000 ft

Answer: (C)

Understanding how many air conditioning packs are needed to meet cabin cooling and pressurization demands at a given altitude shows why this limit exists. When only one pack is operating, the cooling capacity and the mass flow of conditioned air are reduced. As you climb, the ambient air becomes thinner, so the system must work harder to keep cabin temperature and pressure within acceptable limits. At a certain altitude, a single pack can no longer meet those demands reliably, so the aircraft is limited to using a single pack up to that point. For this aircraft, that ceiling is 31,000 feet. Beyond that, both packs are needed to maintain cabin conditions, so 31,000 ft is the maximum altitude for single-pack operation.