Which air source cools hydraulic systems 1 and 2 during flight?

• A. Ram air from the ram air scoop passing over the heat exchanger
• B. Pack air from the environmental control system
• C. External ambient air
• D. Engine bleed air

Answer: (A)

Hydraulic systems shed heat by forcing air over a heat exchanger that sits in the hydraulic line. During flight, that cooling air comes from ram air delivered by the ram air scoop. As the aircraft moves fast, the pressure difference pushes outside air through ducts and across the heat exchanger, carrying away heat from the hydraulic fluid.

This source is best because it provides a steady, high-flow cooling medium without adding heat to the system. Pack air from the environmental control system is intended for cabin conditioning and isn’t the primary supply for hydraulic cooling. External ambient air by itself wouldn’t move through the exchanger without a dedicated airflow path, and engine bleed air is hot and used for other systems rather than cooling hydraulic fluid.