on engine shutdown (in both cases the pressure to the
fire- wall shutoff valve is cut off), the firewall valve
Description. The oxygen system (fig. 2-24) is
provided primarily as an emergency system, however,
the system may also be used to provide supplemental
(first aid) oxygen. Two 70 cubic-foot capacity oxygen
supply cylinders, charged with aviator's breathing
oxygen, are installed in the unpressunrized portion of
the aircraft behind the aft pressure bulkhead. The pilot's
and copilot's positions are equipped with diluter demand
type regulators, which automatically mix the proper
amount of oxygen for a given amount of air at altitude.
A first aid oxygen mask is also provided in the cabin.
Oxygen system pressure is shown by two gages
placarded OXYGEN SUPPLY PRESSURE, located on
the pilot's and copilot's oxygen regulator control panels.
Two pressure reducers, located in the unpressurized
portion of the aircraft behind the aft bulkhead, lower the
pressure in the system to 400 PSI, and route oxygen to
the regulator control panels. Both cylinders are
interconnected, so refilling can be accomplished through
a single filler valve located in the aft right side of the
fuselage exterior. A pressure gage is mounted in
conjunction with the filler valve, and each cylinder has a
pressure gage. Table 2-4 shows oxygen flow planning
rates vs. altitude. Table 2-5 shows oxygen duration
capacities of the system in liters per minute (LPM) per
mask at normal temperature and pressure, dry (NTPD).
(1) Regulator control panels.
A valid cause for alarm would be the rapid
loss of oxygen pressure when the aircraft is
above 12,500 feet. Should this condition
arise, descend as rapidly as possible to an
altitude which does not require the use of
When not in use, the diluter control lever
should be left in the 100% OXYGEN
position to prevent regulator contamination.
Each regulator control panel contains a blinker-type flow
indicator, a 500 PSI pressure gage, a red emergency
pressure control lever placarded EMERGENCY -
NORMAL - TEST MASK, a white diluter control lever
placarded 100% OXYGEN - NORMAL OXYGEN, and a
green supply control lever placarded ON - OFF. The
diluter control lever selects either normal or 100%
oxygen when the emergency pressure control lever is in
the NORMAL position
(2) The emergency pressure control lever has
consumption for the individual using oxygen, and the
remaining position serves for testing hose and mask
integrity. In the EMERGENCY position, the control
lever causes 100% oxygen to be delivered at a safe,
positive pressure. In the NORMAL position, the lever
allows delivery of normal or 100% oxygen, depending
upon the selection of the diluter control lever. In the
TEST MASK position, 100% oxygen at positive pressure
is delivered to check hose and mask integrity.
Check to ensure that the OXYGEN SUPPLY
pressure before each flight When oxygen is
in use, a check of the supply pressure
should be made at intervals during flight, to
approximate the supply duration. The
outside temperature is reduced as an
aircraft ascends to higher altitudes. Oxygen
change will show a pressure drop. This type
of drop in pressure will rise again upon
return to a lower or warmer altitude.
provided on the oxygen control panels should never
indicate over 400 PSL If the pressure exceeds 400 PSL
a malfunction of the pressure reducer is indicated.
Whenever oxygen is inhaled, a blinker-vane slides into
view within the flow indicator window, showing that
oxygen is being released When oxygen is exhaled, the
blinker vane vanishes from view.
Pure oxygen will support combustion. Do
not smoke while oxygen is in use.
Oxygen masks for the pilot and copilot are provided. To
connect a mask into the oxygen system, the individual
connects the line attached to the mask to the flexible
hose which is attached to the cockpit sidewall. The
microphone in the oxygen mask is connected to the
headset/oxygen mask microphone selector switch,
located on the instrument panel (fig. 2-15). To test
mask and hose integrity, the individual