How do the air conditioning packs operate and what happens if a pack fails?

• A. Packs generate power for the electrical system.
• B. Packs condition bleed air for cabin air; if a pack fails, the remaining pack continues; the failed pack is isolated.
• C. Packs cool the avionics only.
• D. Packs are not used on narrowbody.

Answer: (B)

Air conditioning packs take bleed air from the engines (or the APU) and condition it to provide cabin air, supplying a comfortable and pressurized environment for passengers and crew. The process involves cooling the hot, high-pressure bleed air using heat exchangers and an air-cycle machine, then delivering the conditioned air to the cabin through the environmental control system. To ensure reliability, there are typically two packs. If one pack develops a fault, its isolation valve closes so the pack is taken out of service, and the other pack remains operating to continue supplying conditioned air. This redundancy keeps cabin conditioning available even with a single pack fault. The other options don’t reflect what packs do or how redundancy is handled: they don’t generate electrical power, they condition cabin air rather than only avionics, and narrowbody aircraft do use air conditioning packs.