What is an Air Cycle Machine?

• A. Cycles hot air into cold air
• B. Compresses air to generate electrical power
• C. Filters cabin air
• D. Heats air with electric coils

Answer: (A)

An Air Cycle Machine is part of the aircraft environmental control system that cools cabin air by using a Brayton-cycle process. It takes hot, high‑pressure bleed air from the engines, drives the cycle to pressurize and cool that air, and then expands it through a turbine. The expansion lowers the air’s temperature, delivering the resulting cold, conditioned air to the cabin. This cooling action—turning hot air into cold air—is what the Air Cycle Machine does, without generating electrical power, acting primarily as a filter, or heating air with electric coils (heating is handled by separate heaters or other components).