the surface may burst, causing hemorrhages in the
ears, eyes, and breathing passages.
The outside air temperature also changes with
altitude. For example, at approximately 18,000
feet the outside air temperature will be 4°F
( 20°C), and at approximately 37,000 feet the
outside air temperature will be 67°F ( 55°C).
Above 37,000 feet the air continues to thin, but
the air temperature will remain constant for
several miles and then begin to rise slowly. Thus,
the lowest outside air temperature to be
encountered by an aircraft would occur at a height
of about 7 miles.
NOTE: The conversion formula for con-
verting Fahrenheit to Celsius (centigrade)
is ~ (F-32).
For example, 4°F is converted as
Conversion of a Celsius temperature to a
Fahrenheit reading is accomplished using the
For example, 55°C is converted as
Remember not to drop the + and signs when
These variations in outside air temperature and
atmospheric pressure are considered by the air-
craft manufacturer when designing the aircraft.
Pressurization and air conditioning of aircraft
are necessary at high altitudes. With operational
ceilings now in excess of 50,000 feet, flight
personnel, and in some cases aircraft components,
are supplied with an artificial means of maintain-
ing a reasonable pressure around the entire body
and/or equipment. This is done be sealing off the
entire cabin/cockpit and any equipment area that
may require pressurization and maintaining an in-
side air pressure equivalent to that at substantially
lower altitudes. This is known as the pressurized
cabin, cockpit, or compartment, as applicable.
In addition to pressurizing them, the cabin,
cockpit, and some compartments are also air-
conditioned if the aircraft is to fly at high speeds.
This requirement is partly due to the difference
in temperatures at various altitudes and also
aerodynamic heating. For example, an aircraft
flying at supersonic speeds at an altitude of 35,000
feet may generate a temperature on its skin of
200°F, and twice that temperature at altitudes
near sea level.
In addition to aerodynamic heating, other
factors affecting cabin/cockpit temperatures are
engine heat, heat from the sun (solar heat), heat
from the electrical units, and heat from the body.
Through research and tests, it was determined that
the average total temperature of these five heat
sources will raise the cabin/cockpit temperature
to approximately 190°F (88°C). Through ex-
periments it was determined that the maximum
temperature that a person can withstand and
maintain efficiency for extended periods is 80°F
(27°C); therefore, air conditioning of the
cabin/cockpit area is just as essential as
pressurization. Under low-speed operating con-
ditions at low temperature, cabin/cockpit heating
may be required.
The proper operation of much of todays air-
craft electronic equipment is also dependent on
maintaining a reasonable operating temperature
that will prolong the life of various components.
In most cases equipment cooling is provided by
teeing off with ducting from the cabin/cockpit
system. On other aircraft a separate cooling
system may be used primarily for equipment
Learning Objective: Recognize the need for
environmental control systems.
The combined pressurization and air con-
ditioning of the cabin is the function of the air-
craft pressurization and air-conditioning system;
a system now in all naval aircraft. The inspection
and maintenance of this system is one of the
important duties of the AME. There are five
requirements necessary for the successful
functioning of a pressurization and air-
1. The cabin must be designed to withstand
the necessary pressure differential. This is