Which feature of air conditioning packs makes them favorable for use in aircraft?

Air conditioning packs are designed for aircraft with an emphasis on reliability and operational efficiency, which is why being relatively trouble-free is a significant feature. In aviation, equipment must perform consistently under various conditions, including changes in altitude and temperature. Aircraft experience unique environments where mechanical failures can lead to serious safety concerns. Therefore, an air conditioning system that operates seamlessly without frequent maintenance or breakdowns is crucial for ensuring passenger comfort and safety during flight.

The other options do not align with the operational requirements of aircraft air conditioning systems. Traditional refrigerants may not be the most efficient or environmentally friendly choice now, and excessive cooling can lead to discomfort for passengers. Large size is impractical in aviation design, where space and weight are critical factors. Therefore, the reliability and trouble-free operation of air conditioning packs make them favorable for use in aircraft.