AIRCRAFT OXYGEN SYSTEMS

Oxygen Systems      

During the maintenance of the oxygen system, the aircraft manufacturer's information must be followed along with the safety requirements men­tioned earlier. Some general rules concerning oxygen system maintenance that must be followed are: keep hands, tools and working area clear of grease, dirt, water and all foreign matter. All oxygen system components must be keep clean and dry until they are installed. The use of com­pounds on fitting threads is normally not allowed unless the aircraft service manual calls for their use. Always check the oxygen cylinder for con­tamination, the hydrostatic test date, and for being completely empty. If the cylinder is found to be completely empty the cylinder generally needs to be sent for a complete inspection by an FAA ap­proved repair station. After a thorough inspection of all the components in the system, an operational check should be performed to ensure the system is functioning normally. The specific inspection procedures for the aircraft that is being serviced will be in the aircraft's service manual; follow these closely.

The following instructions are to serve as a guide for the in­spection and maintenance of aircraft oxygen systems. The information is applicable to both portable and permanently-installed equipment.

7.7.1 Aircraft Gaseous Oxygen Systems: The oxygen in gaseous systems is supplied from one or more high or low-pressure oxy­gen cylinders. Since the oxygen is compressed within the cylinder, the amount of pressure in­dicated on the system gauge bears a direct re­lationship to the amount of oxygen contained in the cylinder. The pressure-indicating line connection is normally located between the cylinder and a pressure-reducing valve.

NOTE: Some of the gaseous oxygen systems do not use pressure-reducing valves. The high pressure is reduced to a useable pressure by a regulator. This regulator is located between the high- and low-pressure system.

CAUTION: Oxygen rich environ­ments are dangerous.

7.7.2   Portable Oxygen Systems: The three basic types of portable oxygen systems are: demand, pressure demand, and continuous flow. The components of these systems are identical to those of a permanent installation with the exception that some parts are minia­turized as necessary. This is done in order that they may be contained in a case or strapped around a person's shoulder. It is for this port­ability reason that special attention be given to assuring that any storage or security provision for portable oxygen equipment in the aircraft is adequate, in good condition, and accessible to the user.

NOTE: Check portable equipment including its security provisions fre­quently, since it is more susceptible to personnel abuse than a permanently installed system.

INSPECTION

Hands, clothing, and tools must be free of oil, grease, and dirt when working with oxygen equipment. Traces of these organic materials near compressed oxy­gen may result in spontaneous combustion, explosions, and/or fire.

Oxygen Tanks and Cylinders: In­spect the entire exterior surface of the cylinder for indication of abuse, dents, bulges, and strap chafing.

(1)       Examine the neck of cylinder for cracks, distortion, or damaged threads.

(2)       Check the cylinder to determine if the markings are legible.

(3)       Check the date of the last hydro­static test. If the periodic retest date is past, do not return the cylinder to service until the test has been accomplished.

(4)       Inspect the cylinder mounting bracket, bracket hold-down bolts, and cylin­der-holding straps for cracks, deformation, cleanliness, and security of attachment.

(5)       In the immediate area where the cylinder is stored or secured, check for evi­dence of any types of interference, chafing, de­formation, or deterioration.

 Lines and Fittings:

(1)       Inspect oxygen lines for chafing, corrosion, flat spots and irregularities, i.e., sharp bends, kinks, and inadequate security.

(2)       Check fittings for corrosion around the threaded area where lines are joined. Pres­surize the system and check for leaks. See paragraph 7.9.2(2) (d)

CAUTION: In pressurizing the sys­tem, actuate the valve slowly to avoid surging which could rupture the line.

Regulators, Valves, and Gauges:

(1)       Examine all parts for cracks, nicks, damaged threads or other apparent damage.

(2)       Actuate the regulator controls and the valve to check for ease of operation.

(3)       Determine if the gauge is function­ing properly by observing 'the pressure build-up and the return to zero when the system oxygen is bled off.

Masks and Hoses:

(1)       Check the oxygen mask for fabric cracks and rough face seals. If the mask is a full-face model, inspect the glass or plastic for cleanliness and state of repair.

(2)       When appropriate, with due regard to hygienic considerations, the sealing quali­ties of an oxygen mask may be tested by placing a thumb over the connection at the end of the mask tube and inhaling very lightly. Re­move the thumb from the disconnect after each continuous inhalation. If there is no leakage,, the mask will adhere tightly to the face during inhalation, and definite resistance to inhalation will be noticeable.

(3)       Flex the mask hose gently over its entirety and check for evidence of deteriora­tion or dirt.

(4)       Examine the mask and hose storage compartment for cleanliness and general con­dition.

(5)       If the mask and hose storage com­partment is provided with a cover or release mechanism, thoroughly check the operation of the mechanism.

MAINTENANCE.

Oxygen Tanks, Cylinders, and Hold Down Brackets.

(1)       Remove from service any cylinders that show signs of abuse, dents, bulges, cracks, distortion, damaged threads, or defects which might render them unsafe. Typical examples of oxygen cylinder damage..

(2)       When replacing an oxygen cylinder, be certain that the replacement cylinder is of the same size and weight as the one removed.