What are the main components of the A321 ECS?

• A. Bleed air from engines/APU, two air conditioning packs, cabin pressure controller, outflow valves, and temperature control
• B. Bleed air from engines/APU; two air conditioning packs; cabin pressure controller; outflow valves
• C. Bleed air from engines/APU, two air conditioning packs, cabin pressure controller, outflow valves, and temperature control
• D. Bleed air from engines only; one air conditioning pack

Answer: (C)

Environmental Control System on the A321 is responsible for delivering conditioned air, maintaining cabin pressure, and regulating temperature for comfort and safety. The main components are the bleed air source from engines or the APU; two air conditioning packs that condition the air; a cabin pressure controller that keeps the cabin at the desired altitude by adjusting the valve positions; outflow valves that vent cabin air to regulate pressure; and a temperature control system that sets and maintains the cabin temperature by controlling the temperature of the air supplied and mixing as needed. All five work together to provide breathable, comfortable air at the correct pressure and temperature. If any part is missing, the system can’t properly control either pressure or temperature. The other options omit one or more essential elements, such as the temperature control or the presence of both packs, making them incomplete.