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Pilot's Handbook of Aeronautical Knowledge
Aircraft Systems
Oxygen Systems

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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




Cabin pressurization instruments.
Figure 6-42. Cabin pressurization instruments.

Physiologically, decompressions fall into two categories:
• Explosive decompression—a change in cabin pressure
faster than the lungs can decompress, possibly causing
lung damage. Normally, the time required to release
air from the lungs without restrictions, such as
masks, is 0.2 seconds. Most authorities consider any
decompression that occurs in less than 0.5 seconds to
be explosive and potentially dangerous.

• Rapid decompression—a change in cabin pressure
in which the lungs decompress faster than the cabin,
resulting in no likelihood of lung damage.

During an explosive decompression, there may be noise, and
one may feel dazed for a moment. The cabin air fills with
fog, dust, or flying debris. Fog occurs due to the rapid drop in
temperature and the change of relative humidity. Normally,
the ears clear automatically. Air rushes from the mouth and
nose due to the escape of air from the lungs, and may be
noticed by some individuals.

Rapid decompression decreases the period of useful
consciousness because oxygen in the lungs is exhaled rapidly,
reducing pressure on the body. This decreases the partial
pressure of oxygen in the blood and reduces the pilot's
effective performance time by one-third to one-fourth its
normal time. For this reason, an oxygen mask should be worn
when flying at very high altitudes (35,000 feet or higher). It
is recommended that the crewmembers select the 100 percent
oxygen setting on the oxygen regulator at high altitude if
the aircraft is equipped with a demand or pressure demand
oxygen system.

The primary danger of decompression is hypoxia. Quick,
proper utilization of oxygen equipment is necessary to avoid
unconsciousness. Another potential danger that pilots, crew,
and passengers face during high altitude decompressions is
evolved gas decompression sickness. This occurs when the
pressure on the body drops sufficiently, nitrogen comes out
of solution, and forms bubbles that can have adverse effects
on some body tissues.

Decompression caused by structural damage to the aircraft
presents another type of danger to pilots, crew, and
passengers––being tossed or blown out of the aircraft if
they are located near openings. Individuals near openings
should wear safety harnesses or seatbelts at all times when
the aircraft is pressurized and they are seated. Structural
damage also has the potential to expose them to wind blasts
and extremely cold temperatures.

Rapid descent from altitude is necessary if these problems are
to be minimized. Automatic visual and aural warning systems
are included in the equipment of all pressurized aircraft.

Oxygen Systems

Most high altitude aircraft come equipped with some type
of fixed oxygen installation. If the aircraft does not have
a fixed installation, portable oxygen equipment must be
readily accessible during flight The portable equipment
usually consists of a container, regulator, mask outlet,
and pressure gauge. Aircraft oxygen is usually stored in
high pressure system containers of 1,800–2,200 psi. When
the ambient temperature surrounding an oxygen cylinder
decreases, pressure within that cylinder decreases because
pressure varies directly with temperature if the volume of
a gas remains constant. If a drop in indicated pressure on a
supplemental oxygen cylinder is noted, there is no reason to
suspect depletion of the oxygen supply, which has simply
been compacted due to storage of the containers in an
unheated area of the aircraft. High pressure oxygen containers
should be marked with the psi tolerance (i.e., 1,800 psi) before
filling the container to that pressure. The containers should
be supplied with aviation oxygen only, which is 100 percent
pure oxygen. Industrial oxygen is not intended for breathing
and may contain impurities, and medical oxygen contains
water vapor that can freeze in the regulator when exposed to
cold temperatures. To assure safety, periodic inspection and
servicing of the oxygen system should be done.