Regulators approved for use up to 40,000' are designed to provide zero percent cylinder oxygen and 100% cabin air at cabin altitudes of 8,000' or less, with the ratio changing to 100% oxygen and zero percent cabin air at approximately 34,000' cabin altitude [Figure 1]
Regulators approved up to 45,000' are designed to provide 40% cylinder oxygen and 60% cabin air at lower altitudes, with the ratio changing to 100% at the higher altitude
Pilots should avoid flying above 10,000' without oxygen during the day and above 8,000' at night
Smoking during any oxygen equipment use is prohibited
Before each flight, the pilot should thoroughly inspect and test all oxygen equipment
When inspecting, make sure your hands are clean of oils and greases, which may ignite if exposed to oxygen
After any oxygen use, verify that all components and valves are closed
Aircraft Oxygen System Designs:
There are a variety of different oxygen systems and delivery methods available to general and commercial aviation, including:
Generally used on large aircraft in an emergency to provide a 10-minute oxygen supply.
Activated by a lanyard on the oxygen mask, a chemical reaction with sodium chlorate is triggered as the user pulls the mask to their face.
Once this system is activated, it must burn out and require replacement.
Chemical oxygen is lightweight and compact.
Oxygen tanks are normally green in color.
Oxygen candles are used on airliners.
No more than 0.005 ml of water per 1 liter of oxygen = 99.5% O2.
Portable Gaseous Oxygen Systems:
Portable gaseous oxygen system provides oxygen when required for aircraft which lack an integral oxygen system.
These systems are used for passengers or crew members when the aircraft oxygen systems services only the pilot and copilot, or when the crew's duties require them to move about the aircraft.
A portable unit weighs approximately 20 pounds and typically consists of a lightweight steel oxygen cylinder (usually 1800 Pounds per Square Inch (PSI), capacity varies), associated plumbing, combined flow control/reducing valve pressure gauge, and a breathing mask and connecting hose.
Portable equipment usually consists of:
Container.
Regulator.
Mask outlet.
Pressure gauge.
On-Board Oxygen Generating Systems:
On-Board Oxygen Generating System, or OBOGS, converts engine compressor bleed air to oxygen-rich breathing air and pressurized air at the correct pressure and temperature.
OBOGS provides the crew with a continuous supply of breathing air while the engine operates.
Components include a heat exchanger, concentrator, regulator, and associated plumbing.
Liquid Oxygen Systems:
Liquid oxygen systems, or LOX, are used in some jet aircraft because LOX storage occupies less space and weighs less than those used for gaseous oxygen.
LOX systems typically consist of converters, check valves and manifolds, an oxygen heat exchanger, an oxygen/vent airflow control panel, a liquid quantity indicator, and a breathing mask with connecting hoses.
Supplemental Oxygen Delivery Systems:
Pilot Handbook of Aeronautical Knowledge, Oxygen Regulator
TThere are numerous types and designs of oxygen masks in use.
The most critical factor in oxygen mask use is to ensure the masks and oxygen system are compatible.
Crew masks are fitted to the user's face with a minimum of leakage and usually contain a microphone
Most masks are the oronasal type, which covers only the mouth and nose
A passenger mask may be a simple, cup-shaped rubber molding sufficiently flexible to prevent individual fitting
It may have a simple elastic head strap, or the passenger may hold it to his or her face
All oxygen masks should be clean to reduce the danger of infection and prolong the life of the mask
To clean the mask, wash it with a mild soap and water solution and rinse it with clear water
If a containing a microphone, use a clean swab, instead of running water, to wipe off the soapy solution
The mask should also be disinfected
A gauze pad that has been soaked in a water solution of Merthiolate can be used to swab out the mask
This solution used should contain a one-fifth teaspoon of Merthiolate per quart of water
Wipe the mask with a clean cloth and air dry
Both pressure and diluter-demand systems use a diaphragm operated demand valve, which opens when suction from inhalation is present
This makes the system more efficient
Cannula:
Pilot Handbook of Aeronautical Knowledge, Cannula With Green Flow Indicator
A cannula is an ergonomic piece of plastic tubing that runs under the nose and is often used to administer oxygen in non-pressurized aircraft [Figure 2]
Cannulas are typically more comfortable than masks and can be used up to 18,000'
Not authorized above 18,000'; therefore, altitudes greater than 18,000' require the use of an oxygen mask
Many cannulas have a flow meter in the line, and if equipped, a periodic check of the green flow detector should be part of a pilot's regular scan
Pilot Handbook of Aeronautical Knowledge, Cannula With Green Flow Indicator
Continuous-Flow Oxygen System:
Pilot Handbook of Aeronautical Knowledge, Continuous Flow
Passenger aircraft generally utilize continuous-flow oxygen systems
The passenger mask typically has a reservoir bag, which collects oxygen from the continuous-flow oxygen system when the mask user is exhaling
The oxygen collected in the reservoir bag allows a higher aspiratory flow rate during the inhalation cycle, which reduces the amount of air dilution
Ambient air is added to the supplied oxygen during inhalation after the reservoir bag oxygen supply is depleted
The exhaled air releases to the cabin [Figure 3]
Electrical Pulse-Demand Oxygen System:
Portable electrical pulse-demand oxygen systems deliver oxygen by detecting an individual's inhalation effort and provide oxygen flow during the initial portion of inhalation
Pulse demand systems do not waste oxygen during the breathing cycle because oxygen only delivers during inhalation
Compared to continuous-flow systems, the pulse-demand method of oxygen delivery can reduce the amount of oxygen needed by 50-85%
Most pulse-demand oxygen systems also incorporate an internal barometer that automatically compensates for changes in altitude by increasing the amount of oxygen delivered for each pulse as altitude is increased [Figure 4]
Pilot Handbook of Aeronautical Knowledge, Portable Pulse-Demand-System
Continuous Flow:
Usable up to 25,000'
Provide a constant delivery of oxygen
Cost-efficient and simple operation
Constant-Flow:
Delivers a constant amount of O2, inefficient at low altitudes
Adjustable-flow: Increases O2 duration by allowing the user to adjust a regulator valve for different altitudes manually
Altitude-compensated: Works like adjustable-flow, but utilizes barometric pressure to adjust O2 for changing altitudes automatically
These systems can be either built in or portable
Oronasal re-breathers: cover both nose and mouth and use a re-breather bag to mix oxygen and exhaled air
Cannula, which inserts into the nose
As altitude increases, the ratio of O2 in the bag increases because of decreased ambient air pressure
Check valves allow for exhaled air to exit the mask at high altitudes completely
General flow rates are 120 liters per hour for crew and 90 liters per hour for passengers
Diluter-Demand:
Diluter-demand oxygen systems supply oxygen only when the user inhales through the mask
An auto-mix lever allows the regulators to automatically mix cabin air and oxygen or supply 100% oxygen, depending on the altitude
The demand mask provides a tight seal over the face to prevent dilution with outside air
Diluter-demand provides sufficient O2 up to 40,000'
A pilot who has a beard or mustache should ensure it will not interfere with the sealing of the oxygen mask
Pressure-Demand:
Pressure-demand oxygen systems are similar to diluter demand oxygen equipment, except that oxygen is supplied to the mask under pressure at cabin altitudes above 34,000'
Pressure-demand regulators create airtight and oxygen-tight seals, but they also provide a positive pressure application of oxygen to the mask facepiece that allows the user's lungs to pressurize with oxygen
Pressure-demand is used above 40,000' because even with 100% O2, the atmospheric pressure is too low to allow proper saturation into the bloodstream
Some systems may have a pressure-demand mask with the regulator attached directly to the mask rather than mounted on the instrument panel or other area within the flight deck
The mask-mounted regulator eliminates the problem of a long hose that must be purged of air before 100% oxygen begins flowing into the mask
Supplemental Oxygen System Components:
Oxygen Containers:
Containers (tanks) are green in color
Aircraft oxygen stores in high-pressure system containers of 1,800-2,200 PSI
When the ambient temperature surrounding an oxygen cylinder decreases, the pressure within that cylinder decreases because pressure varies directly with temperature if the volume of a gas remains constant
If indicated pressure on a supplemental oxygen cylinder drops, there is no reason to suspect depletion of the oxygen supply, which has compressed due to storage of the containers in an unheated area of the aircraft
High-pressure oxygen containers have markings with the psi tolerance (i.e., 1,800 psi) before filling the container to that pressure
Service containers with aviation oxygen only, which is 100% pure oxygen
Industrial oxygen is not intended for breathing and may contain impurities, and facepiece oxygen masks may contain water vapor that can freeze in the regulator when exposed to cold temperatures
To assure safety, pilots should do periodic inspection and servicing of the oxygen system
Safety Precautions:
Oxygen is an oxidizer, supporting combustion, and an extremely hazardous material in the aviation environment
Acting as a catalyst, small sparks or fires in the presence of combustibles such as oils, fuels, and other chemicals can quickly grow
Purge hoses before coupling to aircraft filler valves to avoid contamination
Containers need to be filled in a controlled manner to avoid overheating
Keep oil and grease away from oxygen equipment, including tools and protective clothing to avoid contamination
Use spark-free tools (brass) when servicing oxygen systems
Do not open valves of an oxygen system or cylinder when a flame, electrical arc, or any other source of ignition is in the immediate area
Take extreme caution not to touch implements containing liquid oxygen without gloves due to the extremely low temperature
Use protective clothing when working with LOX including gloves, coveralls, face shields, and LOX boots
Never seal or cap the vent port of a LOX system
Vent design ensures sufficient flow capacity to carry away LOX that may escape
The expansion ratio of liquid oxygen is 862 to 11-liquid oxygen at atmospheric pressure will a generate pressure of up to 12,000 PSI
If allowed to evaporate in a sealed container or system which has no relief provisions, LOX could cause an explosion
Never saturate cloth, wood, grease, oil paint, or tar with LOX
LOX by itself will not burn, but mixing it with any material will cause the LOX to boil and splash violently with possible combustion
Pulse Oximeters:
Amazon, Portable Fingertip Pulse Oximeter
A pulse oximeter is a device that measures the amount of oxygen in an individual's blood, in addition to heart rate
This non-invasive device measures the color changes that red blood cells undergo when they become saturated with oxygen
By transmitting a special light beam through a fingertip to evaluate the color of the red cells, a pulse oximeter can calculate the degree of oxygen saturation within one percent of directly measured blood oxygen
Because of their portability and speed, pulse oximeters are very useful for pilots operating in non-pressurized aircraft above 12,500' where supplemental oxygen is required
A pulse oximeter permits crew-members and passengers of an aircraft to evaluate their actual need for supplemental oxygen [Figure 5]
Pilots must always check aircraft oxygen systems for accessibility inflight and operational function
An easy acronym to remember how is "PRICE:
Pressure
Regulator (check quantity)
Indicators
Connections
Emergency
Oxygen System Servicing:
Before servicing any aircraft with oxygen, consult the specific aircraft service manual to determine the type of equipment required and procedures to be used
Observe precautions whenever servicing aircraft oxygen systems
Oxygen system servicing should be accomplished only when the aircraft is outside of the hangars
Personal cleanliness and good housekeeping are imperative when working with oxygen
Oxygen under pressure and petroleum products create spontaneous results when in contact with each other
Service people should be certain to wash dirt, oil, and grease (including lip salves and hair oil) from their hands and tools before working around oxygen equipment
Aircraft with permanently installed oxygen tanks usually require two persons to accomplish servicing of the system
One should remain at the service equipment control valves, with the others located where he or she can observe the aircraft system pressure gauges
Oxygen system servicing is not recommended during aircraft fueling operations or while other work is performed that could provide a source of ignition
Oxygen system servicing while passengers are on board the aircraft is not recommended
Cleaning Oxygen Masks:
All oxygen masks should be clean to reduce the danger of infection and prolong the life of the mask.
To clean the mask, wash it with a mild soap and water solution and rinse it with clear water.
If it contains a microphone, use a clean swab, instead of running water, to wipe off the soapy solution.
The mask should also be disinfected.
A gauze pad that has been soaked in a water solution of Merthiolate can be used to swab out the mask.
This solution should contain one-fifth teaspoon of Merthiolate per quart of water.
Wipe the mask with a clean cloth and air dry.
Pilot Handbook of Aeronautical Knowledge, Portable Pulse-Demand-System
SCUBA Diving Recommendations:
A pilot or passenger who intends to fly after scuba diving should allow the body sufficient time to rid itself of excess nitrogen absorbed during diving
Decompression sickness can occur from evolved gas creating a serious in-flight emergency
8,000' MSL and below:
The recommended waiting time before going to flight altitudes of up to 8,000 feet is at least 12 hours after diving which has not required controlled ascent (non-decompression stop diving), and at least 24 hours after diving which has required controlled ascent (decompression stop diving)
Above 8,000' MSL:
The waiting time before going to flight altitudes above 8,000 feet should be at least 24 hours after any SCUBA dive
These recommended altitudes are actual flight altitudes above mean sea level (AMSL) and not pressurized cabin altitudes
This takes into consideration the risk of decompression of the aircraft during flight
Private Pilot (Airplane) Operation of Aircraft Systems Airman Certification Standards:
Objective: To determine whether the applicant exhibits satisfactory knowledge, risk management, and skills associated with safe operation of systems on the airplane provided for the flight test.
Private Pilot (Airplane) Operation of Aircraft Systems Skills:
The applicant exhibits the skills to:
PA.I.G.S1:
Operate at least three of the systems listed in K1a through K1l appropriately.
PA.I.G.S2:
Complete the appropriate checklist(s).
Supplemental Oxygen Case Studies:
NTSB Identification: WPR12FA154: The National Transportation Safety Board determines the probable cause(s) of this accident to be: The in-flight loss of control due to the pilot's impairment as a result of hypoxia. Contributing to the accident was the pilot's operation of the airplane above 12,500' without the aid of supplemental oxygen
NTSB Identification: CEN09LA527: The National Transportation Safety Board determines the probable cause(s) of this accident to be: The in-flight loss of control due to the pilot's impairment as a result of hypoxia. Contributing to the accident was the pilot's decision to operate the unpressurized airplane at an altitude requiring supplemental oxygen without having any oxygen available
Supplemental Oxygen Knowledge Quiz:
Conclusion:
Note that while the percentage of oxygen in the atmosphere does not decrease, pressure for the body to absorb it does, necessitating supplemental oxygen
Note the connection between supplemental oxygen and hypoxia in our case studies
These rules are in place because others have died from it
At night, especially when tired, these effects may occur as low as 5,000 feet
Therefore, for optimum protection, pilots are encouraged to use supplemental oxygen above 10,000 feet cabin altitude during the day and above 5,000 feet at night
Be sure you're following your Pilot Information Manual as applicable for the appropriate use of oxygen systems
While subjective, oxygen use when operating near the required altitudes for it may also improve alertness and therefore decision making
Realize that while operating near, but below, altitudes requiring oxygen, passengers may still find themselves experiencing distress without it
