Ask Captain Dan Baz : Our Resident Pilot Answers Flight Questions. Cabin Pressure – March 18, 2012

CFN – Pilot Dan Baz is answering your flying questions here on the Cornwall Free News. If you have a question about flying you can email Captain Dan or post below.

How is an airplane cabin pressurized ?

The cabin air system in airliners is designed to provide a safe, comfortable cabin environment at cruising altitudes that can reach above 40,000 feet.  At those altitudes, the cabin must be pressurized to enable passengers and crew to breathe normally. By regulation, the cabin pressure cannot be less than the equivalent of outside air pressure at 8,000 feet.

Pressurized air for the cabin comes from the compressor stages in the airplane’s jet engines.  This outside air, passing through engine compressors, gets very hot as it becomes pressurized. It is cooled by air conditioning units.

The cooled air then flows to a chamber where it is mixed with an approximately equal amount of highly filtered air from the passenger cabin. The combined outside and filtered air is ducted to the cabin and distributed through overhead outlets. Inside the cabin, the air flows in a generally circular patterns and exits through floor grilles on either side of the cabin.  The exiting air goes below the cabin floor into the lower lobe of the fuselage.  About half of the air exiting the cabin is exhausted from the airplane through an outflow valves in the lower lobe.  The outflow valve controls the cabin pressure.

The air in the cabin is completely replaced every two to three minutes. The air is of much better quality than air in an average home or an office building.

A bit more about Captain Dan:

Captain Dan Baz enrolled in Flight School at the age of 16.
He has completed studies in Aircraft Engineering and Master of Business Administration. He has been at the controls of many different types of aircraft, from single engine Cessnas to large intercontinental jets on global routes.
Over the last four decades he has flown thousands of hours up in the blue sky.

Have a question for the Captain ? Send it to Captain Dan Baz Every week a question from the readers will be selected and answer posted in this column.

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