Which statement about RAM air and Bleed air is correct?

• A. RAM air and Bleed air always mix
• B. RAM air and Bleed air are the same source
• C. RAM air and Bleed air do not mix
• D. RAM air is used for cabin pressurization

Answer: (C)

RAM air and bleed air serve different roles in the aircraft’s environmental control system. Bleed air is taken from an engine compressor and used as the source for cabin air after it’s cooled and conditioned. RAM air is outside air used specifically to cool that bleed air in the heat exchangers of the air conditioning packs. The two streams stay separate; they don’t merge into one cabin air flow. The cabin air that ends up in the cabin comes from the conditioned bleed air, not directly from RAM air. So the statement that they do not mix is correct.

The other options fail because RAM air and bleed air are not from the same source, they do not routinely mix into a single supply, and RAM air is not used directly to pressurize the cabin.