necessary to show that it is extremely improbable. As noted in the earlier advisory material regarding System Design Analysis (AC 25.1309-1), "If a quantitative analysis is used to help show compliance with Federal Aviation Regulations for equipment which is installed and required only for a specific operating condition for which the airplane is thereby approved, credit may not be taken for the fact that the operating condition does not always exist." While this note does not appear in AC 25.1309-1A, the basic philosophy has not changed.
(2) Guidance, Availability of Flightcrew Oxygen. The following policy was extracted from an FAA memorandum dated May 11, 1992, in response to an FAA Safety Recommendation regarding annunciation that oxygen is available for use by the flightcrew when in actuality there is no oxygen available.
(a) On a recent twin-engine transport airplane flight, the crew elected to divert after the first officer donned his oxygen mask and discovered he had no oxygen available. After landing, the crew oxygen bottle valve was found turned to the closed position. Prior to the flight, maintenance had started to replace the bottle due to low pressure, and the valve located at the bottle was turned off. When the bottle pressure was found to be acceptable, the bottle was reinstalled but the valve was left turned off and safety wired in that position. The maintenance crew checked the bottle pressure on the airplane Engine Indication and Crew Alerting System (EICAS) status page and because the EICAS displays the pressure in the line downstream of the valve, the residual pressure in the line resulted in a displayed pressure that was within limits.
(b) The existing system on this airplane measures the oxygen pressure in the line to the flightcrew regulator. If the shutoff valve at the pressure bottle is shut off, there is sufficient pressure remaining in the line to indicate a pressure high enough for dispatch. Even when the crew checks the masks, only a small amount of oxygen is allowed to escape, and there are currently no means to determine that the valve is off. Further, the oxygen pressure, and therefore the quantity, is observable on EICAS only when the crew selects the status page.
(c) The FAA determined that this is unacceptable for the following reasons:
1 . Section 25.1441(c) requires that the crew be able to determine the quantity of oxygen available. When the valve is in the "OFF" position, the oxygen is not available, but the indication on EICAS (the residual pressure in the line) is that oxygen is available if needed.
The pressure measurement gives information about quantity only when the valve is open. If the valve is inadvertently left closed, the information provided is misleading.
2 . Section 25.1309(c) states: “Warning information must be provided to alert the crew to unsafe system operating conditions, and to enable them to take appropriate corrective action. Systems, controls, and associated monitoring and warning means must be designed to minimize crew errors which could create additional hazards.” It is clear that the existing design gives misleading information to the flightcrew, which could lead them into an unsafe operation. If depressurization takes place at a significant altitude, and oxygen is not available to the crew, an unsafe condition exists.
3 . Further, § 121.333(c)(4) states: "Before the takeoff of a flight, each flight crewmember shall personally preflight his oxygen equipment to insure that the oxygen mask is functioning, fitted properly, and connected to appropriate supply terminals, and that the oxygen supply and pressure are adequate for use." In theory, adherence to this rule should ensure that the oxygen supply is available.
(d) In order for the scenario discussed above to be a hazard, four separate events would have to occur:
1 There would have to be maintenance performed on the airplane oxygen system that required the valve, located on the oxygen bottle, to be turned off for some reason.
The airplane maintenance manual contains both visual and operational checks to ensure that the oxygen valve is open and the pressure is adequate. These procedures were not followed in the case of interest because the bottle was never removed.
2 The flightcrew check of their oxygen equipment would have to fail to indicate that oxygen is not available. This is possible with the present preflight procedure, but the procedure is being changed.
3 A decompression would have to occur that required the use of oxygen by the flightcrew.
4 Event 3 would have to occur before the flightcrew had attempted to use supplemental oxygen (which would demonstrate no oxygen available) or checked the EICAS Status Page, which would indicate low oxygen pressure. In either case, airline procedures and Federal Aviation Regulations require that the crew divert to fix the problem.
(e) The manufacturer of the airplane involved in the incident which prompted this memorandum is changing their operational procedures, which are used by the airlines for their Operations Manuals, to describe an acceptable procedure to verify that adequate oxygen is available at the pilots mask. This procedure involves two separate flow tests (Normal and 100 percent), followed by a pressure check on EICAS. As all flightcrew masks must be tested (at least two on any transport category airplane), there will be ample tests and pressure checks to identify a problem prior to dispatch. Based on the above considerations, the FAA has determined an adequate level of safety is achieved through the existing and proposed procedures with the certificated design. However, this mechanization is not considered to meet the requirements of § 25.1309(c).
(f) Flightcrew oxygen systems should be reviewed to ensure that on future certification programs, a system design that can lead to misinformation is not allowed.
(3) Oxygen Installation for Medical Use. The following policy was extracted from an FAA facsimile message dated January 3, 1991, that was written in response to a request for policy relative to the installation of shutoff valves, pressure relief devices and overboard vent lines installed on oxygen bottles for medical use.
(a) There is no current written FAA policy relative to the installation of manifolded oxygen systems other than Civil Aeronautics Manual (CAM) 4b.651-1. CAM 4b.651-1 recommends that low pressure oxygen systems have a pressure relief device to prevent over pressurization during the filling operation.
(b) Department of Transportation (DOT) regulation (49 CFR, § 173.34(d)) requires that all pressure cylinders be provided with a safety device (a rupture disc) to prevent explosion of the bottle if the bottle is subjected to over-pressure or excessive heat. The pressure relief device may be installed on the bottle or on the valve of the bottle (on the pressure side of the valve).
(c) To meet the requirements of § 25.1441(b) and § 1451(c) (note: Amendment 25-72 deleted § 25.1451 and moved the requirements to § 25.869(c)), aircraft manufacturers have been installing oxygen systems that have a pressure relief that vents through a vent line, normally stainless steel, to the outside of the aircraft. A colored blowout plug is installed at the end of the vent line on the surface of the aircraft to indicate if the rupture disc has blown.
(d) The inquiring FAA office indicated that they may have approved single high pressure bottle (air ambulance) installations that do not have the overboard drain line. Further, these single bottle installations are filled off the airplane. There may be other installations without a vent line because there doesn't appear to be a written policy on this subject.
(e) To determine if a vent line is needed to comply with §§ 25.1441(b) and § 25.869(c)(3) (formerly 25.1451(c)), the consequences of the pressure relief device venting the total contents of the bottle or bottles (if manifolded together) into the compartment should be considered, i.e., overpressurizing the compartment; exposure to grease, flammable fluids and ignition sources.
(f) All the installations, which the FAA is aware of, have a high pressure shutoff valve located on the bottle to isolate the bottle from the oxygen system. On a manifolded system, these valves normally are lockwired in the open position. However, the bottle shutoff valve is downstream of the pressure relief device in order that the pressure relief device will protect the bottle from exploding if the bottle is isolated (valve shut) from the system and is exposed to heat or over- pressurization.
(g) The FAA is not aware of any objection to having a common high pressure manifold without the bottle shutoff valves as long as there is a manifold system shutoff valve and a pressure relief device between the bottles and the shutoff valve.
(h) One objection might be exposing the airplane and maintenance personnel to the hazards of a fully pressurized vented bottle or bottles if someone tries to remove a bottle from the system. The total system has to be depressurized before the bottle can be removed as opposed to the manifold system where each bottle shutoff valve can be closed, and an individual bottle with its valve can be removed.
(i) In general, industry practice has been to separate and isolate the oxygen system from sources of ignition. Ignition sources include pumps, motors, and electrical equipment associated with the medical installations as well as the aircraft equipment. Further, the manufacturers normally install a pressure relief device with an overboard vent line.
e. Reference. The address for ordering the document listed below can be found in the Appendix to this AC.
The Society of Automotive Engineers (SAE) has aerospace committees that prepare documents reflecting industry standards and practices. The SAE A-10 Committee, Aircraft Oxygen Equipment, has prepared a handbook, “1992 SAE Aircraft Oxygen Equipment Handbook,” containing all Aerospace Standards, Aerospace Recommended Practices, and Aerospace Information Reports related to oxygen equipment published by SAE. While not regulatory in nature, this handbook contains information that may be of interest to an applicant.
64. SECTION 25.1443 - MINIMUM MASS FLOW OF SUPPLEMENTAL OXYGEN.
a. Rule Text.
(a) If continuous flow equipment is installed for use by flight crewmembers, the minimum mass flow of supplemental oxygen required for each crewmember may not be less than the flow required to maintain, during inspiration, a mean tracheal oxygen partial pressure of 149 mm. Hg. when breathing 15 liters per minute, BTPS, and with a maximum tidal volume of 700 cc. with a constant time interval between respirations.
(b) If demand equipment is installed for use by flight crewmembers, the minimum mass flow of supplemental oxygen required for each crewmember may not be less than the flow required to maintain, during inspiration, a mean tracheal oxygen partial pressure of 122 mm. Hg., up to and including a cabin pressure altitude of 35,000 feet, and 95 percent oxygen between cabin pressure altitudes of 35,000 and 40,000 feet, when breathing 20 liters per minute BTPS. In addition, there must be means to allow the crew to use undiluted oxygen at their discretion.
(c) For passengers and cabin attendants, the minimum mass flow of supplemental oxygen required for each person at various cabin pressure altitudes may not be less than the flow required to maintain, during inspiration and while using the oxygen equipment (including masks) provided, the following mean tracheal oxygen partial pressures:
(1) At cabin pressure altitudes above 10,000 feet up to and including 18,500 feet, a mean tracheal oxygen partial pressure of 100 mm. Hg. when breathing 15 liters per minute, BTPS, and with a tidal volume of 700 cc. with a constant time interval between respirations.
(2) At cabin pressure altitudes above 18,500 feet up to and including 40,000 feet, a mean tracheal oxygen partial pressure of 83.8 mm. Hg. when breathing 30 liters 156
per minute, BTPS, and with a tidal volume of 1,100 cc. with a constant time interval between respirations.
(d) If first-aid oxygen equipment is installed, the minimum mass flow of oxygen to each user may not be less than four liters per minute, STPD. However, there may be a means to decrease this flow to not less than two liters per minute, STPD, at any cabin altitude. The quantity of oxygen required is based upon an average flow rate of three liters per minute per person for whom first-aid oxygen is required.
(e) If portable oxygen equipment is installed for use by crewmembers, the minimum mass flow of supplemental oxygen is the same as specified in paragraph
(a) or (b) of this section, whichever is applicable.
b. Intent of Rule. The requirements of this rule provide standards to ensure that oxygen dispensing equipment will protect passengers and crewmembers from the effects of hypoxia.
The requirements for flight crewmembers are provided in terms of mean tracheal partial pressure of oxygen, which is not easily measured in certification testing. Dispensing equipment is, however, designed to provide the required oxygen flow. This equipment is, in most cases, approved through the technical standard order system. Requirements for passenger and cabin crewmember equipment are expressed in terms of oxygen flow rates.
c. Background. Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). The requirements in § 4b.651(b) of the CAR were carried over essentially unchanged to § 25.1443 of 14 CFR.
d. Policy/Compliance Methods. There is no written policy or guidance in our files.
e. Reference. The address for ordering the document listed below can be found in the Appendix to this AC.
The Society of Automotive Engineers (SAE) has aerospace committees that prepare documents reflecting industry standards and practices. The SAE A-10 Committee, Aircraft Oxygen Equipment, has prepared a handbook containing all Aerospace Standards, Aerospace Recommended Practices, and Aerospace Information Reports related to oxygen equipment published by SAE. While not regulatory in nature, this handbook contains valuable information that may be of interest to an applicant.
65. SECTION 25.1445 - EQUIPMENT STANDARDS FOR THE OXYGEN DISTRIBUTING SYSTEM.
a. Rule Text.
(a) When oxygen is supplied to both crew and passengers, the distribution system must be designed for either-
(1) A source of supply for the flight crew on duty and a separate source for the passengers and other crewmembers; or
(2) A common source of supply with means to separately reserve the minimum supply required by the flight crew on duty.
(b) Portable walk-around oxygen units of the continuous flow, diluter-demand, and straight demand kinds may be used to meet the crew or passenger breathing requirements.
b. Intent of Rule. This rule addresses the oxygen distribution system and does not address oxygen dispensing equipment (masks), the standards for which are addressed in § 25.1447.
c. Background. Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). The requirements in § 4b.651(c) of the CAR were carried over essentially unchanged to § 25.1445 of 14 CFR, except for the standards on potable walk-around units that are found in § 25.1445(b).
d. Policy/Compliance Methods. There is no written policy or guidance in our files.
e. Reference. The address for ordering the document listed below can be found in the Appendix to this AC.
The Society of Automotive Engineers (SAE) has aerospace committees that prepare documents reflecting industry standards and practices. The SAE A-10 Committee, Aircraft Oxygen Equipment, has prepared a handbook, “1992 SAE Aircraft Oxygen Equipment Handbook,” containing all Aerospace Standards, Aerospace Recommended Practices, and Aerospace Information Reports related to oxygen equipment published by SAE. While not regulatory in nature, this handbook contains information that may be of interest to an applicant.
66. SECTION 25.1447 - EQUIPMENT STANDARDS FOR OXYGEN DISPENSING UNITS.
a. Rule Text.
If oxygen dispensing units are installed, the following apply:
(a) There must be an individual dispensing unit for each occupant for whom supplemental oxygen is to be supplied. Units must be designed to cover the nose and mouth and must be equipped with a suitable means to retain the unit in 158
position on the face. Flight crew masks for supplemental oxygen must have provisions for the use of communication equipment.
(b) If certification for operation up to and including 25,000 feet is requested, an oxygen supply terminal and unit of oxygen dispensing equipment for the immediate use of oxygen by each crewmember must be within easy reach of that crewmember. For any other occupants, the supply terminals and dispensing equipment must be located to allow the use of oxygen as required by the operating rules in this chapter.
(c) If certification for operation above 25,000 feet is requested, there must be oxygen dispensing equipment meeting the following requirements:
(1) There must be an oxygen dispensing unit connected to oxygen supply terminals immediately available to each occupant, wherever seated, and at least two oxygen dispensing units connected to oxygen terminals in each lavatory. The total number of dispensing units and outlets in the cabin must exceed the number of seats by at least 10 percent. The extra units must be as uniformly distributed throughout the cabin as practicable. If certification for operation above 30,000 feet is requested, the dispensing units providing the required oxygen flow must be automatically presented to the occupants before the cabin pressure altitude exceeds 15,000 feet. The crew must be provided with a manual means of making the dispensing units immediately available in the event of failure of the automatic system.
(2) Each flight crewmember on flight deck duty must be provided with a quickdonning type oxygen dispensing unit connected to an oxygen supply terminal.
This dispensing unit must be immediately available to the flight crewmember when seated at his station, and installed so that it:
(i) Can be placed on the face from its ready position, properly secured, sealed, and supplying oxygen upon demand, with one hand, within five seconds and without disturbing eyeglasses or causing delay in proceeding with emergency duties; and
(ii) Allows, while in place, the performance of normal communication functions.
(3) The oxygen dispensing equipment for the flight crewmembers must be:
(i) The diluter demand or pressure demand (pressure demand mask with a diluter demand pressure breathing regulator) type, or other approved oxygen equipment shown to provide the same degree of protection, for airplanes to be operated above 25,000 feet.
(ii) The pressure demand (pressure demand mask with a diluter demand pressure breathing regulator) type with mask-mounted regulator, or other approved oxygen equipment shown to provide the same degree of protection, for airplanes operated at altitudes where decompressions that are not extremely improbable may expose the flightcrew to cabin pressure altitudes in excess of 34,000 feet.
(4) Portable oxygen equipment must be immediately available for each cabin attendant.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-41, 42 FR 36971, Jul. 18, 1977; Amdt. 25-87, 61 FR 28696, Jun. 5, 1996]
b. Intent of Rule. This rule addresses the oxygen dispensing units, including oxygen masks and regulators, and do not address oxygen distributing systems, the standards for which are addressed in § 25.1445.
c. Background. Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). Many of the requirements in § 4b.651(d) of the CAR for oxygen dispensing units were carried over essentially unchanged to § 25.1447 of 14 CFR.
(1) Amendment 25-41 (July 18, 1977) added requirements for a manual means for the crew to make the dispensing units available in the event of a failure of the automatic means, and that the masks for use by the flight crewmembers be of the quick donning type.
(2) Amendment 25-87 (June 5, 1996) added flightcrew oxygen equipment requirements for a pressure demand type with mask-mounted regulator, or other approved equipment, for airplanes operated at altitudes where decompressions that are not extremely improbable may expose the flightcrew to cabin pressure altitudes in excess of 34,000 feet.
d. Policy/Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of this rule and the following information.
(1) Oxygen Equipment for Forward Observer's Position. The following policy was extracted from an FAA memorandum dated February 1, 1988, that was written to provide guidance for certification of forward observer's oxygen equipment.
(a) The requirements for a forward observer's seat are contained in § 25.785(k), § 121.581(a), § 125.317(b), and § 135.75(b). In parts 121, 125, and 135 of 14 CFR, there is no specific list of required equipment for the first observer's seat, but rather a general statement that the required equipment would be "determined by the Administrator." The FAA considers a representative of the Administrator, occupying the first observer's seat and performing official duties, to be a required crewmember. This designation also applies to a company check airman, or other person performing official duties relating to the performance of the crew or operation of the airplane. This person would be expected to interact with the captain and other flight crewmembers, in addition to his or her normal duties relating to enroute inspection and surveillance. For these reasons, it is important that the occupant of the observer seat be provided with the equipment necessary to perform his or her function, e.g., oxygen, protective breathing equipment, and communication via a radio and interphone panel which is the same type equipment provided to the flightcrew.
(b) Section 25.785(l) does not specify what type of equipment must be provided at the observer seat as part of the type design. The rule states, “Each forward observer’s seat required by the operating rules must be shown to be suitable for use in conducting the necessary enroute inspection.” Section 25.785(l) has been interpreted to allow the use of passenger-type oxygen equipment, provided that the airplane in question is not to be used in Part 121, 125, or 135 operation. If the airplane is to be so used, the oxygen, communication, and protective 160
breathing requirements stated above must be provided. If the airplane is not to be used in parts 121, 125, or 135 operation (i.e., in Part 91 operation), installation of either type of oxygen equipment at the first observer's seat is adequate to show compliance with the requirements of § 25.1441, Oxygen Equipment and Supply, and installation of communication equipment and protective breathing equipment would be optional.
(c) The duration of oxygen supply should be commensurate with the crew supply, since protection may be necessary due to a delayed descent following decompression, protective breathing requirements, or other extended usage.
e. References. The addresses for ordering the latest revision of technical standard orders and other referenced documents listed below can be found in the Appendix to this AC.
TSO-C64a, Oxygen Mask Assembly Continuous Flow, Passenger (For Air Carrier Aircraft).
TSO-C78, Crewmember Demand Oxygen Masks.
TSO-C89, Oxygen Regulators, Demand.
TSO-C99, Protective Breathing Equipment.
TSO-C116, Crewmember Protective Breathing Equipment.
The Society of Automotive Engineers (SAE) has aerospace committees which prepare documents reflecting industry standards and practices. The SAE A-10 Committee, Aircraft Oxygen Equipment, has prepared a handbook, “1992 SAE Aircraft Oxygen Equipment Handbook,” containing all Aerospace Standards, Aerospace Recommended Practices, and Aerospace Information Reports related to oxygen equipment published by SAE. While not regulatory in nature, this handbook contains information that may be of interest to an applicant.
67. SECTION 25.1449 - MEANS FOR DETERMINING USE OF OXYGEN.
a. Rule Text.
There must be a means to allow the crew to determine whether oxygen is being delivered to the dispensing equipment.
b. Intent of Rule. The standards in this section ensure that the flightcrew is able to determine that oxygen is being dispensed properly.
c. Background. Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). The requirement in § 4b.651(e) of the CAR that there be a means for the crew to determine that oxygen is being delivered to the dispensing equipment (masks) were carried over essentially unchanged to § 25.1449 of 14 CFR.
d. Policy/Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of this rule and the following information. Compliance with this section is usually 161
accomplished by the use of flow indicators in the oxygen regulators (for flight crewmembers) and in the oxygen tubes leading to the masks (for passenger equipment).
(1) Oxygen Equipment for Observer Position. The following policy was extracted from an FAA letter dated April 19, 1996, in response to an inquiry concerning the requirement for supplemental oxygen flow indication at the observers' stations.
(a) An applicant proposed installing mask-mounted regulators without flow indication at the observers' stations. This configuration has been certified for previous versions of the same airplane model. It was the applicant’s position that the FAA exempts mask-mounted regulators from the § 25.1449 flow indication requirement. They cited FAA Technical Standard Order (TSO) C-89, which exempts mask-mounted regulators from the TSO requirement to provide a means to indicate oxygen flow from the regulator outlet. Although the TSO allows omission of flow indicators for mask-mounted regulators, it is not an authorization to install such items on transport airplanes. However, the FAA reviewed the original certification data for the airplane model in question, and the background of § 25.1449. Based on this review, the FAA determined that installation of the mask-mounted regulators without flow indicators at the observers' stations meets the intent of § 25.1449.
(b) The background for § 25.1449 is found in the FAA Civil Aeronautics Manual (CAM) 4b. Section 25.1449 states: "There must be a means to allow the crew to determine whether oxygen is being delivered to the dispensing equipment." Similarly, § 4b.651 of the Civil Air Regulation (CAR) states: "Means shall be provided to enable the crew to determine whether oxygen is being delivered to the dispensing units." Although flow indicators for each individual passenger or flight crew station represent one method of compliance, policy guidance provided in § 4b.651-10 of the CAR (for crew systems) and § 4b.651-11 of the CAR (for passenger systems) allows operators to establish procedures for checking the oxygen flow to individual oxygen users. For passenger diluter-demand systems, § 4b.651-11 of the CAR states that the procedure may be "checking of the oxygen flow by a trained crewmember by momentarily moving the regulator lever to Automix ‘OFF’ (100% OXYGEN) while the mask is being worn."
Lack of oxygen flow would be "immediately evidenced by the user's inability to inhale while wearing his mask."
(c) The FAA is satisfied that § 25.1449 does not specifically require flow indicators at each mask. Although these indicators are generally provided, other methods of flow indication are not precluded. Therefore, the FAA is satisfied that flow indicators are not required at the observers' stations for certification, provided that the applicant incorporates suitable design features and procedures to ascertain flow at the observers' stations. On the model in question, supplemental oxygen for the flightcrew and the observers' stations is provided by a common source. Flow of oxygen from the source is split between the flight crew and observers' stations by a "T" fitting. Under normal operations, all cockpit masks are set for "100% OXYGEN." At this setting, lack of flow would be immediately detected by the user. The FAA is requiring incorporation of a preflight check of the observers' masks in the airplane flight manual (AFM).
In addition, a positive indication of flow at the flightcrew stations by the flow indicators installed at those stations would indicate that oxygen is also flowing to the observers' stations. The FAA 162
is satisfied that the system design, the preflight inspection procedure, and flow indicators at the flightcrew stations are adequate to meet the intent of § 25.1449.
(2) Determination of Passenger Oxygen Supply. The following policy was extracted from an FAA memorandum dated January 8, 1996, which addresses compliance with § 25.1449 for a design that will determine, from the flightdeck, that oxygen is flowing to the passenger supplemental oxygen masks. It is noted that 14 CFR does not require a means for the flightcrew to make this determination while on flight deck duty. A number of airplanes have gaseous supplemental oxygen systems which do not have a specific indication of oxygen flow on the flight deck. Compliance with 14 CFR requirements is usually shown through use of a flow indicating device in the oxygen mask tubing. Technical Standard Order TSO-C64a, and the associated Society of Automotive Engineers Aerospace Standard SAE-AS 8025, require a means for the crew to determine that oxygen is flowing. This is usually accomplished with a small device that provides a green indication when the flow rate exceeds 0.5 liters per minute. A cabin crewmember verifies from the indicator whether or not oxygen is flowing. If there are no cabin crewmembers, this would require a flight crewmember to leave their station and check. The FAA has determined that this would not be a viable option during an emergency such as a decompression.
e. References. None.
68. SECTION 25.1450 - CHEMICAL OXYGEN GENERATORS.
a. Rule Text.
(a) For the purpose of this section, a chemical oxygen generator is defined as a device which produces oxygen by chemical reaction.
(b) Each chemical oxygen generator must be designed and installed in accordance with the following requirements:
(1) Surface temperature developed by the generator during operation may not create a hazard to the airplane or to its occupants.
(2) Means must be provided to relieve any internal pressure that may be hazardous.
(c) In addition to meeting the requirements in paragraph (b) of this section, each portable chemical oxygen generator that is capable of sustained operation by successive replacement of a generator element must be placarded to show-
(1) The rate of oxygen flow, in liters per minute;
(2) The duration of oxygen flow, in minutes, for the replaceable generator element; and
(3) A warning that the replaceable generator element may be hot, unless the element construction is such that the surface temperature cannot exceed 100 degrees F.
[Amdt. 25-41, 42 FR 36971, Jul. 18, 1977]
b. Intent of Rule. The standards in this rule ensure that chemical oxygen generators safely provide oxygen.
c. Background. The standards in this section address chemical oxygen generators. This subject was not addressed in either part 4b of the CAR or part 25 when it was originally codified.
This section was added at Amendment 25-41, July 18, 1977.
d. Policy/Compliance Methods. There is no written policy or guidance in our files.
e. Reference. The address for ordering the latest revision of the document listed below can be found in the Appendix to this AC.
The Society of Automotive Engineers (SAE) has aerospace committees that prepare documents reflecting industry standards and practices. The SAE A-10 Committee, Aircraft Oxygen Equipment, has prepared a handbook, “1992 SAE Aircraft Oxygen Equipment Handbook,” containing all Aerospace Standards, Aerospace Recommended Practices, and Aerospace Information Reports related to oxygen equipment published by SAE. While not regulatory in nature, this handbook contains information that may be of interest to an applicant.
69. SECTION 25.1453 PROTECTION OF OXYGEN EQUIPMENT FROM RUPTURE.
a. Rule Text.
Oxygen pressure tanks, and lines between tanks and the shutoff means, must be-
(a) Protected from unsafe temperatures; and
(b) Located where the probability and hazards of rupture in a crash landing are minimized.
b. Intent of Rule. This rule ensures that the oxygen equipment is not exposed to unsafe temperatures and minimizes the possibility of rupture in the event of a crash landing.
c. Background. Effective February 1, 1965, part 25 was added to Title 14, Code of Federal Regulations (14 CFR) to replace part 4b of the Civil Air Regulations (CAR). The requirements in § 4b.651(g) of the CAR were carried over essentially unchanged to § 25.1453 of 14 CFR.
d. Policy/Compliance Methods. For guidance on compliance with this requirement, refer to the preamble of this rule and the following information.
(1) Flexible Plastic Oxygen Lines. The following policy was extracted from an FAA memorandum dated December 27, 1983, to provide guidance regarding the use of flexible plastic tubing for oxygen distribution lines. While this guidance was generated for Part 23 airplanes, it is equally applicable for part 25 airplanes.