TM 1-1510-225-10
2-83
nozzle. The mixed air is then forced into the bleed
airline routed to the cabin.
Bleed airflow is controlled automatically. When
the aircraft is on the ground, circuitry from the landing
gear safety switch prevents ambient air from entering
the flow control unit to provide maximum heating.
The bleed air firewall shutoff valve in the control
unit is a spring-loaded bellows-operated valve that is
held in the open position by bleed air pressure. When
the electric solenoid is shut off, or when bleed air
diminishes on engine shutdown (in both cases the
pressure to the firewall shutoff valve is cut off), the
firewall valve closes.
2-61. OXYGEN SYSTEM.
a. Description. The oxygen system, Figure
2-24, is provided primarily as an emergency system;
however, the s ystem may also be used to provide
supplemental (first aid) oxygen. One 77 cubic-foot
capacity oxygen supply cylinder, charged with aviator's
breathing oxygen, is installed in the unpressurized
portion of the aircraft behind the aft pressure bulkhead.
The pilot's and copilot's positions are equipped with
mask mounted diluter demand/100% regulators, which
automatically mix the proper amount of oxygen for a
given amount of air at altitude. Drop out masks are
provided for passengers. A first aid oxygen mask is
also provided in the cabin. A gauge, placarded
OXYGEN, located on the copilot's subpanel displays
oxygen supply pressure. Oxygen system refilling is
accomplished through a single filler valve located on
the aft right side of the fuselage exterior. The oxygen
system control circuit is protected by a 5-ampere
circuit
breaker
placarded
OXYGEN
CONTROL,
located on the right sidewall circuit breaker panel.
Table 2 -5 shows oxygen flow planning rates vs
altitude. Table 2-6 shows oxygen duration capacities
of the system in liters per minute (LPM) per mask at
normal temperature and pressure, dry (NTPD). Figure
2-25 provides a graph that depicts oxygen cylinder
capacity.
b. Oxygen System Operation. A push/pull
oxygen on/off control handle, located on the left side of
the control pedestal, arms the automatically deployed
passenger
oxygen
system
and
applies
oxygen
pressure to the crew masks. Pulling this handle out
opens a valve on the oxygen cylinder that is located aft
of the aft pressure bulkhead. When this handle is
pushed in, no oxygen will be available anywhere in the
aircraft. To ensure oxygen availability, the oxygen
on/off control handle should be pulled and the
OXYGEN pressure gauge, located on the copilot's
subpanel, should be checked prior to engine start.
c. Oxygen Duration. The oxygen system is
based on an adequate oxygen flow for a pressure
altitude of 35,000 feet. The passenger masks and
oxygen duration chart, Table 2-6, is based on a flow
rate of 3.9 liters per minute – normal temperature and
pressure, dry (LPM-NTPD). For oxygen duration
computation, each diluter demand mask being used is
counted as two masks at 3.9 LPM-NTPD.
d. Pilot and Copilot Oxygen Masks. The pilot
and copilot are each provided with a diluter-demand
quick donning oxygen mask stored overhead in the
cockpit. The crew masks are stowed with the oxygen
hose plugged in so that oxygen will be immediately
available when required. This does not cause a loss
of oxygen since the diluter demand masks will deliver
oxygen only upon inhalation.
