From the Flight Deck (Captain Doug Morris)

Keeping Cabin Air Fresh

Captain Doug Morris answers your questions about aviation.

Q: How is the cabin air kept fresh? Are filters used? David Clements, Canberra, Australia
Cabin air is continually bled from the engines. This conditioned air is then mixed with a nearly equal amount of highly filtered cabin air. A HEPA (high efficiency particulate air) system filters the air much like filters in hospital surgical rooms. Compared to buildings, however, airliners have even better filtration, a higher air-change rate and a higher proportion of outside air. Cabin air is exchanged every two and a half to three minutes – i.e. flushed 20 to 25 times every hour.