Which option best describes how avionics are cooled?

• A. Ambient underfloor air
• B. Avionics exhaust fan
• C. Ambient underfloor air or by the avionics exhaust fan
• D. External air

Answer: (C)

Avionics cooling works by moving air through the avionics bay to carry away heat from the equipment. This can happen with ambient air flowing in from outside or from under the floor (ram air) as the aircraft is moving, which then passes through heat exchangers and exits. If the flight conditions don’t provide enough cooling—such as at low speed or high heat load—a dedicated avionics exhaust fan actively moves air through the bay to augment cooling. Some systems use either method, or both, to ensure adequate cooling across the flight envelope. So the best description is that avionics are cooled by ambient underfloor air or by the avionics exhaust fan.