What role does the cooling turbine play in some air conditioning systems?

• A. Powers the cabin lights
• B. Heats the bleed air
• C. Cooling turbine is used to super-cool the air to 2C
• D. Drives the aircraft propulsion

Answer: (C)

In this type of air conditioning setup, cooling is produced by expanding high‑pressure air in a turbine, which creates a refrigeration effect. The bleed air is cooled and then directed through a cooling turbine (an expander). As the air expands through the turbine, its temperature drops significantly, producing a much cooler air stream that can be used to chill the cabin air through heat exchangers. In some designs, this expansion can bring the air temperature down to around 2°C for the cooling stage, before it’s mixed and tempered to comfortable cabin conditions. That cooling action is the whole point of the cooling turbine: it provides the necessary refrigeration to lower air temperature, unlike powering lights, heating bleed air, or driving propulsion.