In an aircraft environmental control system, what is ram air used for?

• A. To pressurize the cabin.
• B. To supply cooling air for packs and help ventilation/air cycle as needed.
• C. To power the aircraft's electrical systems.
• D. To heat the cabin during cold weather.

Answer: (B)

Ram air is outside air captured by the aircraft as it moves through the atmosphere and used to cool the environmental control system. In the ECS, this air is directed through the heat exchangers in the air conditioning packs, removing heat from the bleed-air stream or from the air cycle machine so the cabin air can be conditioned to a comfortable temperature. It also supports ventilation by providing fresh air flow or aiding the cooling process when needed. It’s not used to pressurize the cabin (that’s done via bleed air and the outflow valve), it doesn’t power electrical systems, and heating the cabin is accomplished with bleed air or electric heaters rather than ram air.