201 - ATPL - The air-conditioning pack of a present-day aircraft consists of several components: these include two heat exchangers the primary exchanger (P) and the secondary exchanger (S). The functions of these heat exchangers are as follows:

Question 201 - Aircraft General Knowledge - Airframe, Systems, Powerplant - ATPL - Airline Transport Pilot license

P: warms up engine bleed air, S: increases the temperature of air originating from the compressor of the pack.

P: warms up engine bleed air, S: recirculates the cabin air, reducing its temperature.

P: pre-cools the engine bleed air, S: increases the temperature of the air used for air-conditioning of cargo compartment (animals).

P: precools the engine bleed air, S: reduces the temperature of the air from the primary exchanger or from the pack's compressor.