Editing Environmental control system (section)

== Air distribution ==
The AC PACK exhaust air is ducted into the pressurized fuselage, where it is mixed with filtered air from the recirculation fans, and fed into the mix manifold. On nearly all modern jetliners, the airflow is approximately 50% outside air and 50% filtered air.

Modern jetliners use high-efficiency particulate arresting [[HEPA]] filters, which trap more than 99% of all [[bacteria]] and clustered [[viruses]].

Air from the mix manifold is directed to overhead distribution nozzles<ref name=nozzles>{{cite magazine |author=Eitel, Elisabeth |url=http://machinedesign.com/fea-and-simulation/cfd-software-automatically-models-how-moving-parts-affect-airflow |title=CFD software models how moving parts affect aircraft-cabin airflow |archive-url=https://web.archive.org/web/20140701053607/http://machinedesign.com/fea-and-simulation/cfd-software-automatically-models-how-moving-parts-affect-airflow |archive-date=2014-07-01 |df=dmy-all |magazine=Machine Design Magazine |date=6 May 2014}}</ref> in the various zones of the aircraft. Temperature in each zone may be adjusted by adding small amounts of trim air, which is low-pressure, high-temperature air tapped off the AC PACK upstream of the TCV. Air is also supplied to individual gasper vents.{{efn|name=gasper|Gaspers are small, circular vents above each passenger seat that can be adjusted by passengers for their personal comfort.}} A revolving control on the vent can be turned to adjust ventilation between no air output at all and a fairly substantial breeze.

[[File:Gasper (aircraft).jpg|thumb|Gasper vent over passenger seats of a [[Boeing 737]]-800]]
Gaspers<ref name=gasper group=lower-alpha/> usually receive their air from the AC PACKs aboard the aircraft, which in turn receive compressed, clean air from the compressor stages of the aircraft's [[jet engine]]s or when on the ground from the [[auxiliary power unit]] (APU) or a ground source. A master control for gaspers is located in the cockpit; gaspers are often temporarily turned off during certain phases of flight (e.g. during take-off and climb) when the load on the engines from [[Bleed air|bleed-air]] demands must be minimized.