Past Cabin Air Systems

Prior to the 1980s‚ Cabin Aircraft Environmental Control Systems (ECS) used 100 percent fresh air (none was re-circulated). This process of compressing and then cooling the outside air to an inhabitable pressure and temperature consumed a significant amount of energy. There was no filtration and there were no cabin air quality standards at that time.

Current Cabin Air Systems 

The use of re-circulated air, combined with outside air, coincided with the introduction of high bypass ratio fan engines. Newer airplane models recirculate as much as 50% of cabin air, decreasing the engine's work. The re-circulated air passes through high-efficiency particulate filters before mixing with conditioned fresh air to re-enter the passenger compartment.