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Pilot's Handbook of Aeronautical Knowledge
Aircraft Systems
Pressurized Aircraft

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




Pressurized Aircraft

Aircraft are flown at high altitudes for two reasons. First, an
aircraft flown at high altitude consumes less fuel for a given
airspeed than it does for the same speed at a lower altitude
because the aircraft is more efficient at a high altitude.
Second, bad weather and turbulence may be avoided by flying
in relatively smooth air above the storms. Many modern
aircraft are being designed to operate at high altitudes, taking
advantage of that environment. In order to fly at higher
altitudes, the aircraft must be pressurized. It is important
for pilots who fly these aircraft to be familiar with the basic
operating principles.

In a typical pressurization system, the cabin, flight
compartment, and baggage compartments are incorporated
into a sealed unit capable of containing air under a pressure
higher than outside atmospheric pressure. On aircraft powered
by turbine engines, bleed air from the engine compressor
section is used to pressurize the cabin. Superchargers may
be used on older model turbine-powered aircraft to pump
air into the sealed fuselage. Piston-powered aircraft may use
air supplied from each engine turbocharger through a sonic
venturi (.ow limiter). Air is released from the fuselage by
a device called an outflow valve. By regulating the air exit,
the outflow valve allows for a constant inflow of air to the
pressurized area. [Figure 6-40]

A cabin pressurization system typically maintains a cabin
pressure altitude of approximately 8,000 feet at the maximum
designed cruising altitude of an aircraft. This prevents rapid
changes of cabin altitude that may be uncomfortable or cause
injury to passengers and crew. In addition, the pressurization
system permits a reasonably fast exchange of air from
the inside to the outside of the cabin. This is necessary to
eliminate odors and to remove stale air. [Figure 6-41]

Pressurization of the aircraft cabin is an accepted method of
protecting occupants against the effects of hypoxia. Within a
pressurized cabin, occupants can be transported comfortably
and safely for long periods of time, particularly if the cabin
altitude is maintained at 8,000 feet or below, where the use
of oxygen equipment is not required. The flight crew in this
type of aircraft must be aware of the danger of accidental
loss of cabin pressure and be prepared to deal with such an
emergency whenever it occurs.

High performance airplane pressurization system.
Figure 6-40. High performance airplane pressurization system.