Which item is NOT part of the PACK air flow path?

Which item is NOT part of the PACK air flow path?

• A. PreCooler
• B. Heat Exchanger (Primary)
• C. Turbine
• D. Filter

Answer: (D)

Air that goes through a PACK follows a cooling and conditioning sequence: bleed air enters, passes through the PreCooler where ram air helps drop the temperature, then goes through the Primary Heat Exchanger for further cooling, and finally moves through the turbine portion of the air cycle machine to achieve the desired low temperature before reaching the cabin. A filter is not part of this PACK flow path; filtration occurs in the cabin air system (such as cabin or recirculation filters) after the pack output. So the item not in the PACK air flow path is the filter.

Air that goes through a PACK follows a cooling and conditioning sequence: bleed air enters, passes through the PreCooler where ram air helps drop the temperature, then goes through the Primary Heat Exchanger for further cooling, and finally moves through the turbine portion of the air cycle machine to achieve the desired low temperature before reaching the cabin. A filter is not part of this PACK flow path; filtration occurs in the cabin air system (such as cabin or recirculation filters) after the pack output. So the item not in the PACK air flow path is the filter.