oxygen systems Flashcards
Normal ‘maximum’ cabin altitude
8000 ft
There is sufficient oxygen & oxygen pressure for humans
Oxygen access is available in which ways:
1) Portable sets
- allows cabin crew to move safely in depressurized cabins
- used for medical assistance
- Usually in aircrafts that fly above 10,000 ft without fixed installed systems
2)stores of gaseous oxygen in central pressurized tanks = DILUTER-DEMAND
- used for flight and cabin crew stations
- Used during depressurization
- Used during smoke & toxic fumes
- automatcially deployed before cabin altitutude reaches 15,000ft
3) Chemically generated gaseous oxygen from gas generators=CONTINUOUS
- provided for passengers (above seats)
**
*doors releasing the masks is pneumatic**
Pressure measurements along the central fixed gaseous oxygen system
Pressure at fixed central store tanks = 1800psi
pressure drops to intermediate pressure
80-100 before it reaches the crew station
pressure reaches crew at 8 to 10 psi
Flight & Cabin Crew Stations
central store of gaseous oxygen
how it works
- Oxgen is charged through a charging point
- Charged oxygen passes through NRV to not return back to the charging point
- Oxygen passes from NRG throug a filter
- Oxygen passes from filter to thermal compensator to reduce its temperature that might build up since the gas is charged
- Oxygen moves to the cylinder (it’s at 1800psi)
- cylinder has a red safety disc & green cap
- If there is excess pressure in the cyclinder, the red disc ruptures & the green cap blows off revealing the red disc (this is how it’s identified to maintenance team)
- During flight operation, the ‘shut-off valve’ is open
- Pressurized charged oxygen moves through the valve through to a system isolation valve
- system isolation valve helps teh cockpit pressure indicator indicate the gas pressure
- The gas reaches the Pressure Regulator (also has a NRV). Here pressure is 80-100psi
- Oxygen reaches mask units at 8-10psi
Purpose of Thermal compensator
to reduce its temperature that might build up since the gas is charged before it reaches the gaseous tank
Pressures moves in this system through colour coded pipes
High pressure pipes = stainless steel
low pressure pipes = alumium alloys
DILUTER DEMAND SYSTEM
Flight crew oxygen supply - MASK
Oxygen Masks are supplied by Dilluter Demand Oxygen Regulators
air/oxygen supplied as demanded by user’s respiration
starts to operate when ‘user breathes*
Uses a regulator
Diluter regulates the amount/ratio of oxgen to cabin air and it adjusts automatically as altitude changes adn cabin pressure decreases.
In NORMAL-selected setting:
Diluted oxygen is supplied to the maks
When in Normal. & altitude increases to 32-36,000ft
100% is supplied
IF 100% O2 is selected setting/EMERGENCY setting
100% regardless of altitude
TEST
selected for testing masks and leakage (usually done at high pressure)
crew can bypass Normal selection and choose 100% if required
How to use a Donned Mask
- Mask & its combined regulator are usually in a stowage compartment located near the seat
- you can test the mask whilst still in stowage to see if it inflates –> PRESS TO TEST button
- Pinch the red tabs, which releases the mask & inflates the strap so that the mask can be easily donned, shaped and held with one hand
- you can release the red tabs
- Mask can be worn over a head set but advisable to wear the mask under your headphones to hear the radio.
- Mask incorporates a microphone
- Masks are sealed as they provide protection from Noxious fumes
Chemically Oxygen Generators
Continuous flow
Fired at:
* at 14,000 ft
* Manually by flight deck crew
Located in:
* In the PSU - Passenger Service Unit
* bathrooms
* cabin
* smoke hood
Composed of:
* Generator
* Oxygen masks attached to Reservoir bags to not waste O2
* Hoses connected to the generators by lanyard
* indicator shoing that oxygen is flowing
* Supplies O2 and cabin air
Generator made of:
* Steel cylinder
* Sodium chlorate + iron powder
* thermal insulator liner
Chemically Oxygen Gas Generators
Above Passengers
- Chemical generator can supply 6 masks
- 4 masks per 3 seats
- Aircrafts must supply 10% more masks thant there are seats
- The generator turns black after burning mechanism so that it indicates that they were used.
- Shelf life: 10 years
- Masks are not sealed so no protection from noxious/smoke fumes
Note: can be released at any time in case of emergency
The release mechanism is activated:
* electric system for chemical system
* pneomotaic system for gaseous system
it’s visually possible to verify oxygen flows to passenger masks
Chemically Oxygen Gas Generators
How it works
- There is an electric firing mechanism connected to the generator by lanyard
- The mask is enjected from PSU
- Mask are in half hung position
- When lanyard is pulled, the sodium chlorate & Iron ignite and burn at high temperature.
- Thermal insulation keeps temperature controlled
- Oxygen is released at 10 degress above ambient
- Release O2 for 15 - 22 min
Chemically Oxygen Gas Generators
If a mask fails to eject
you can open the mask storage compartment with a sharp object due to a simply latch mechanism.
PulseOx
In A350 and B787
an **Oxygen gaseous cylinder is upplied for every PSU **
There is a microprocessor that supplies **oxygen that is more catered to the user’s need
**
Also supplies 4 masks per 3 seats
Oxygen supply in small aircraft
Typically use a central supply of gaseous oxygen
supplies crew and passengers
in the Flight Manual, use calculations to determine the duration of supply of oxygen based on:
* - aircraft altitude
* - cylinder pressure
* # of passengers
Control and operation on B737
1)guage
* showing o2 pressure
2)Switch showing
* NORMAL = deploys masks automatically based on altitude
* ON = deploys mask regardless of altitude
PASS OX ON visual/light
* indicates that masks have been delployed
Portable Oxygen Tanks & Masks
Used for:
cabin crew to maneovre freely in depressurized cabin
made with:
Light alloy steel tank
Mask & straps for carrying
flow control
pressure reducing valve
Pressure inside the tank
* is 1800psi
* filled 120L of O2
When Used, the supplies the following:
* Normal = 2 L per minute —> 60 min supply
* High = 4 L per minute —> 30 min supply
Smoke hoods
EU regulation dictates the aircraft is equipped for this.
Uses:
Chemical oxygen generator
Must cover:
* eyes
* nose
* mouth
Flight Crew use:
* smoke goggles
* masks
Cabin crew use - NOT PASSENGERS
* head cover/smoke hood
* built in mask with its own chemical oxygen generator
* requires training
* continuous oxygen
* Filteration happens once at inhalation and once at exhlation
* To ensure no contamination with outside air
* 15 - 20 min supply
Smoke mask
full face cover
+
on demand flow
Why oxygen in the system must be dry
because moisture can cause valves to freeze & corrode system components
oxygen will smell bad
How is Oxygen tanks fit for aviation purposes be labelled
AV02
Black tank with white next/green neck
it ensures no moistures is in there
What tanks are not fit for aviation use
medical oxygen
welding oxygen
Safety precautions
Oxygen doesn’t burn but can intensify fire or make substances ignite like:
- combustible material
- sometimes non combustable material such as steel
- Oil & greases
system cannot be over tightened
1. tightning can cause small metal swarf in the system which can ignite.
*such things should be avoided in service
fixed oxygen systems in pressurized aircraft and used to?
to provide O2 when
- during depressurization
- smoke/fumes in cockpit
Difference bt/w Chemical & Gaseious oxygen generators
Usage:
- Chemical: often
- Gaseous: seldom
Switching off/on
- Chemical: can’t be swtiched off
- Gaseous: can be switched on/off + flow control
Supply of O2
- Chemical: 15 min
- Gaseous: over 15 min (depnds on O2 bottol)
maintenance/cost
- Chemical: cheap/easy
- Gaseous: comples
Risk of fire
- Chemical: low
- Gaseous: high
Weight
- Chemical: light
- Gaseous: heavy
Storage
- Chemical: easy
- Gaseous: complex
Reversible function
- Chemical: non reversable
- Gaseous: reverseable
