An example of the use of indicator lights is
AIRCRAFT ELECTROHYDRAULIC
the system used to show high oil temperature. A
AND PNEUMATIC SYSTEMS
thermoswitch in the oil return line closes when the
Learning Objective: Recognize operating
temperature reaches above normal. This usually
provides a path to ground illuminating the OIL
principles and characteristics of aircraft
HOT light. The light goes out only when the oil
electrohydraulic and pneumatic systems.
cools to normal temperature.
The word hydraulics is from the Greek word
for water. Hydraulics originally meant the study
Another application of the use of an indicator
light is the landing gear unlocked warning light.
of physical behavior of water at rest and in
In some aircraft, a red light glows in the
motion. Today the meaning includes the physical
translucent landing gear control lever when the
behavior of all liquids, including hydraulic
gear is not in either the up or down position.
fluid.
Hydraulics is the science of liquid pressure and
flow. In its application to aircraft, hydraulics is
the action of liquids, forced under pressure
REVIEW SUBSET NUMBER 1
through tubing and orifices, to operate various
mechanisms.
Q1. List the two primary purposes of aircraft
lighting.
The primary concern in working with
hydraulics is to control the flow of fluid. You do
this by using solenoids that simply turn on, shut
off a flow of fluid, or change flow direction. In
Q2. Why should spare light bulbs be shock
some cases, electrical devices may schedule a
mounted?
precise amount of fluid flow. In any case, you
must understand the characteristics of liquids.
You should recall from chapter 1 that a liquid
Q3. What are the two most common types of
has no definite shape and conforms to the shape
bulb bases?
of its container. Also, a liquid can be only slightly
compressed. Another fact you should recall is the
ability of a liquid to transmit pressure.
The physics of fluids and basic hydraulic
Q4. What type of light is used to attract visual
principles are contained in Fluid Power,
attention to the aircraft's position and
NAVEDTRA 14105. Study the first two chapters
heading at night?
of this publication with this chapter if you need
to review basic hydraulic principles.
Although some aircraft manufacturers make
Q5. On which wing tip will the green navigation
greater use of hydraulics than others, the
light be found?
hydraulic system of the average modern aircraft
performs many functions. Among the units
commonly operated by hydraulics are the landing
gear, wing flaps, speed brakes, wing folding
Q6. A bluish-green anticollision light identifies
mechanisms, flight control surfaces, canopy,
what type of aircraft?
bomb bay doors, wheel brakes, and arresting gear.
BASIC HYDRAULIC SYSTEM
Q7. When the angle of attack is perfect for the
All hydraulic systems are essentially the same,
landing approach, what color AOA light
regardless of their function. Hydraulics are on the
illuminates?
