What are the common components of an environmental control system?

• A. Engines, landing gear, and wheels
• B. Batteries, antennas, and fuel lines
• C. Packs/air conditioning units, ducts, valves, bleed air sources, control panels
• D. Pistons, gears, and levers

Answer: (C)

The question tests what makes up an aircraft environmental control system—the parts that condition and distribute cabin air. The best answer lists the core hardware: packs or air conditioning units that actually condition the air, the ducts that carry that conditioned air to the cabin and other areas, the valves that regulate flow, temperature, and pressure, the bleed air sources that provide the high‑pressure air needed by the packs (from engines or an APU), and the control panels that let the crew set temperatures and monitor system status. Together, these components enable the ECS to maintain comfortable and safe air quality, temperature, and pressure for occupants and equipment. Other options mix in propulsion, landing gear, batteries, antennas, fuel lines, or simple mechanical parts, which aren’t part of the environmental control system.