Aircraft Systems

The primary danger of decompression is hypoxia. Quick, being stored in an unheated area of the aircraft rather than proper utilization of oxygen equipment is necessary to avoid an actual depletion of the oxygen supply. High pressure unconsciousness. Another potential danger that pilots, crew, oxygen containers should be marked with the psi tolerance and passengers face during high altitude decompressions is (i.e., 1,800 psi) before filling the container to that pressure. evolved gas decompression sickness. This occurs when the The containers should be supplied with oxygen that meets pressure on the body drops sufficiently, nitrogen comes out or exceeds SAE AS8010 (as revised), Aviator’s Breathing of solution, and forms bubbles inside the person that can have Oxygen Purity Standard. To assure safety, periodic inspection adverse effects on some body tissues. and servicing of the oxygen system should be performed. Decompression caused by structural damage to the aircraft An oxygen system consists of a mask or cannula and a presents another type of danger to pilots, crew, and regulator that supplies a flow of oxygen dependent upon passengers––being tossed or blown out of the aircraft if cabin altitude. Most regulators approved for use up to 40,000 they are located near openings. Individuals near openings feet are designed to provide zero percent cylinder oxygen should wear safety harnesses or seatbelts at all times when and 100 percent cabin air at cabin altitudes of 8,000 feet or the aircraft is pressurized and they are seated. Structural less, with the ratio changing to 100 percent oxygen and zero damage also has the potential to expose them to wind blasts percent cabin air at approximately 34,000 feet cabin altitude. and extremely cold temperatures. [Figure 7-43] Most regulators approved up to 45,000 feet are designed to provide 40 percent cylinder oxygen and 60 Rapid descent from altitude is necessary in order to minimize percent cabin air at lower altitudes, with the ratio changing these problems. Automatic visual and aural warning systems to 100 percent at the higher altitude. are included in the equipment of all pressurized aircraft. Pilots should be aware of the danger of fire when using Oxygen Systems oxygen. Materials that are nearly fireproof in ordinary air may be susceptible to combustion in oxygen. Oils and greases may Crew and passengers use oxygen systems, in conjunction ignite if exposed to oxygen and cannot be used for sealing with pressurization systems, to prevent hypoxia. Regulations the valves and fittings of oxygen equipment. Smoking during require, at a minimum, flight crews have and use supplemental any kind of oxygen equipment use is prohibited. Before oxygen after 30 minutes exposure to cabin pressure altitudes each flight, the pilot should thoroughly inspect and test all between 12,500 and 14,000 feet. Use of supplemental oxygen equipment. The inspection should include a thorough oxygen is required immediately upon exposure to cabin examination of the aircraft oxygen equipment, including pressure altitudes above 14,000 feet. Every aircraft occupant, available supply, an operational check of the system, and above 15,000 feet cabin pressure altitude, must have assurance that the supplemental oxygen is readily accessible. supplemental oxygen. However, based on a person’s physical The inspection should be accomplished with clean hands and characteristics and condition, a person may feel the effects should include a visual inspection of the mask and tubing of oxygen deprivation at much lower altitudes. Some people for tears, cracks, or deterioration; the regulator for valve flying above 10,000 feet during the day may experience and lever condition and positions; oxygen quantity; and the disorientation due to the lack of adequate oxygen. At night, location and functioning of oxygen pressure gauges, flow especially when fatigued, these effects may occur as low indicators, and connections. The mask should be donned and as 5,000 feet. Therefore, for optimum protection, pilots are the system should be tested. After any oxygen use, verify that encouraged to use supplemental oxygen above 10,000 feet all components and valves are shut off. cabin altitude during the day and above 5,000 feet at night. Most high altitude aircraft come equipped with some type of fixed oxygen installation. If the aircraft does not have a fixed installation, portable oxygen equipment must be readily accessible during flight. The portable equipment usually consists of a container, regulator, mask outlet, and pressure gauge. Aircraft oxygen is usually stored in high pressure system containers of 1,800–2,200 psi. When the ambient temperature surrounding an oxygen cylinder decreases, pressure within that cylinder decreases because pressure varies directly with temperature if the volume of a gas remains constant. A drop in the indicated pressure of a supplemental oxygen cylinder may be due to the container Figure 7-43. Oxygen system regulator. 7-37