1.
Flight Crew Oxygen
Ever wondered why you have to hold the RESET/TEST switch
down and push the EMERGENCY/Test selector for 5 seconds during preflight?
Trapped air in the supply lines may cause the Flight Crew
Oxygen Pressure Indicator to show sufficient pressure, while the Oxygen
Cylinder SOV
(attached to the cylinder) is closed.
The latter must be turned full counterclockwise to open.
Therefore, at least one crew member should push and hold the Oxygen Mask
Reset/Test switch and Emergency/Test knob for 5 seconds to empty the supply
lines between the mask and the cylinder. Oxygen pressure should not decrease by
more than 100 PSIG during this test. If the pressure drops by more than 100
PSIG, a partially closed Oxygen Cylinder SOV should be suspected
2.
Crew Oxygen System
First
of all I’ll tell you that oxygen is dangerous!! It cannot mix with grease in
anyway causing an explosion. That is the reason when maintainers charge O²,
they wear white coveralls to see if there is any grease visible on their
clothing. O yeah so . . . do NOT use lip chap sticks when using O²!!
A
green oxygen cylinder is mounted in the E&E bay and can be either 114/115
ft³ or 76 ft³. The minimum charge is company related but mostly a rounded up
value regarding the highest temperature and maximum
flight deck occupation (see your PI section in FCOM 1). Maximum allowed
indicated pressure is 1850 PSI but the overboard discharge valve is set at a
whopping 2600 PSI were the green indicator disc located just behind the E&E
bay access blows-out either by overcharging or by thermal expansion.
There
are 2 indicators for pressure, one direct reading gage on the bottle and the
second is on the aft overhead panel which gets an electrical signal from a
pick-up in the manifold and is powered by the Battery Bus.
From
the bottle the pressure is reduced to ± 60 – 85 PSI and has a protection at 100
PSI to prevent a too high pressure toward the regulators.
The
crew regulators have the next options:
Normal – in this position you have to inhale to get a diluted oxygen flow meaning it is a mix of environmental (cockpit) air and oxygen. (no wise during fumes/smoke)
Normal – in this position you have to inhale to get a diluted oxygen flow meaning it is a mix of environmental (cockpit) air and oxygen. (no wise during fumes/smoke)
100% - you’ll inhale 100% oxygen on demand.
EMERGENCY – in this position you get pressurized 100% oxygen through the mask.
There
is a test lever on each regulator to test the oxygen system separately. The
first test is just to slide the RESET/TEST lever backwards were it releases residual
pressure in the mask with a short rush of air and indicating the yellow X flow
indicator.
The
second test needs to be performed in the EMERGENCY position of the regulator
were you first have to identify the crew pressure (in the manifold) than push
the button to test and slide simultaneously the RESET/TEST lever backwards for
5 seconds. This should result in a constant flow of air with the X flow
indication. There should be no more decrease than 100 PSI, a sharp drop-off or
slow increase of pressure on the indicator. When any of the previous occurs the
valve on the bottle is either closed or not completely open. After this don’t
forget to rotate the test button back to 100%.
The
test can be performed together with the mask microphone test (SP 1 in FCOM 1)
through selecting MASK, FLT INT and SPKR on the audio elect panel so you’ll
hear the rush of air through the cockpit speaker when simultaneously pushing
the INT switch during the O² test.
Not all companies perform this test but remember it is emergency
equipment so it can safe your day during Non-Normal procedures as you have to
establish crew communication somewhere
