Na cabine moderna, quase metade do ar da cabine é recirculada. Como este documento informativo da IATA sobre a qualidade do ar da cabine - risco de notas de vírus contagiosos :
The cabin air system is designed to operate most efficiently by delivering approximately 50 percent outside air and 50 percent filtered, recirculated air.
O AIVC também observa em Qualidade do ar em aviões de passageiros :
In early commercial jet aircraft, passenger cabins were ventilated with 100% outside air. In more recent jet aircraft, approximately 50% of the ventilation air is outside air and the remaining 50% is filtered recirculated cabinair.
A razão para usar o ar recirculado é bastante simples - economia de combustível. Do documento Sistema de controle ambiental do avião comercial - Aspectos de engenharia da qualidade do ar da cabine :
At the beginning of the commercial jet airliner age, jet airplanes did not have cabin air recirculation systems,... The primary reason was that early jets were powered by highly inefficient turbojet engines.
As engine technology progressed, turbofans were developed with a core bypass ratio of approximately 2 to 1. Fuel economy improved and the cost of engine bleed air relative to overall fuel consumption was still sufficiently small to make 100% bleed air to the passenger cabin cost effective.
As modern turbofan engines with high 5 to 1 bypass ratios were developed, fuel consumption to provide engine thrust decreased. However, the fuel consumption relative to extracting bleed air dramatically increased, almost in direct proportion to the higher bypass ratio. For a 767 with P&W 4000 engines, the percent increase in fuel consumption due to bleed air only would be almost four times higher than an equivalently sized turbojet for the same amount of bleed air.
Aumento do consumo de combustível de ar de sangria com motores a jato modernos ; imagem de Sistema de Controle Ambiental de Avião Comercial - Aspectos de Engenharia da Qualidade do Ar da Cabine por Elwood H. Hun et. al.
