known ordinarily as flammables or com-
Toxic and poisonous materials (TOXIC). A
line identified by the word TOXIC contains
materials that are extremely hazardous to life
Anesthetics and harmful materials (AAHM).
All materials productive of anesthetic vapors
and all liquid chemicals and compounds
hazardous to life and property, but not
normally productive of dangerous quantities of
fumes, or vapors, are in this category.
Physically dangerous materials (PHDAN). A
line that carries material that is not dangerous
within itself, but that is asphyxiating in
confined areas or is generally handled in a
dangerous physical state of pressure or
temperature, is identified by the marking
Table 6-9 lists some of the fluids with which you
may be required to work and the hazards associated
with each one.
For convenience in distinguishing one hydraulic
line from another, each line is designated as to its
function within the system. In general, the various
hydraulic lines are designated as follows:
Supply lines. Lines that carry fluid from the
reservoir to the pumps are called supply (or suction)
Pressure lines. Lines that carry only pressure are
called pressure lines.
Pressure lines lead from the
pumps to a pressure manifold, and from the pressure
manifold to the various selector valves, or they may
run directly from the pump to the selector valve.
Lines that alternately carry
pressure to an actuating unit and return fluid from the
actuating unit are called operating lines, or working
lines. Each operating line is identified in the aircraft
according to its specific function; for example,
LANDING GEAR UP, LANDING GEAR DOWN,
FLAPS UP, FLAPS DOWN, etc., as the case may be.
Return lines. Lines that are used to return fluid
from any portion of the system to the reservoir are
called return lines.
Vent lines. Lines that carry excess fluid over-
board or into another receptacle are called vent lines.
Table 6-9.Hazards Associated with Various Fluids
Air (under pressure)
LPG (liquid petroleum gas)
Oils and greases
Fabricated tubing and tube assemblies requiring
storage for any length of time should be provided with
protective closures at each end.
Do not use pressure-sensitive tape as a substitute
for protective closures.
Oxygen tube assemblies
require protection of the entire assembly in addition to
protective closures at end fittings. The complete
assembly should be stored and packaged in sealed
plastic bags in accordance with Aviation Crew
Systems Manual Oxygen Equipment, NA 13-1-6.4.
TUBING AND TUBE ASSEMBLIES
Learning Objective: Recognize the mainte-
nance practices and procedures used in the
repair and fabrication of tubing and tube
Maintenance of tube assemblies at the
organizational level is limited to inspection, removal,
installation, repair and replacement. Inspections are
performed during fabrication, installation, and on
During fabrication, inspect