In the environmental control system, what is ram air primarily used for?

• A. To supply cooling air for packs and help ventilation/air cycle as needed.
• B. To pressurize the cabin.
• C. To power the hydraulics.
• D. To heat the cabin.

Answer: (A)

Ram air is used to remove heat from the air conditioning packs. Bleed air from the engines is hot, so it passes through the packs where heat exchangers transfer that heat to ram air flowing across them. This cooling air then helps provide conditioned air for cabin ventilation and environmental control. In short, ram air’s primary role is cooling the packs and aiding ventilation; it does not pressurize the cabin, power hydraulics, or heat the cabin.