use by any crewmember while combating fires on board an airplane. The approval basis was contained in Action Notice A8150.2, dated September 1, 1987, in advance of TSO-C116.
(b) Section 121.337 clearly intends that any crewmember PBE be immediately ready to perform its intended function during an emergency. In fact, the rule requires that each certificate holder's operations manual designate at least one crewmember to check that each PBE unit is properly stowed and serviceable prior to the first-flight of the day.
(c) The approval basis (TSO-C116) for crewmember PBE requires that the equipment has a means to indicate the serviceability of the unit in its stowed condition. Some manufacturers of the crewmember PBE designs approved by the FAA have elected to use a vacuum sealed envelope as a means of protecting the PBE, and the loss of vacuum has been accepted as an indicator that the PBE is not serviceable.
(d) One manufacturer recommended that when the vacuum is lost the PBE need not be replaced immediately, since ambient moisture will not deactivate the potassium superoxide in the atmosphere regenerating system for a number of days. This may well be correct, but it is only one consideration. Since the cause of the loss of vacuum will most likely not be known to the crewmember making the inspection, and the extent of damage to the PBE itself may not be evident, the PBE should be considered not serviceable. Another consideration is that a design, which includes a protective envelope material that can readily be damaged, may not perform its intended function.
(e) Based on the above information, ACO's should ensure that the manufacturer submits operating, installation, and maintenance instructions with limitations, warnings, or cautions for FAA approval. The information being provided the end user should be in accord with the safety intent of § 121.337.
(3) Protective Breathing Equipment on the Flight Deck. The following policy was extracted from an FAA memorandum dated December 19, 1988, and provided additional guidance on protective breathing equipment for use on the flight deck.
(a) Section 121.337 specifies provisions for protective breathing equipment with the airplane both pressurized and unpressurized. Section 25.1439 makes no such distinction.
The part 25 rule specifies that protective breathing equipment must be installed as part of the type design if certain types of cargo compartments or isolated, occupied compartments are installed. If these specified compartments are not installed on the airplane, then protective breathing equipment is not required as part of the type design.
(b) For an unpressurized part 25 airplane certified without these specified compartments and operated under Part 121, however, the decision to require protective breathing equipment should be based on an evaluation of the hazard. Section 25.831(d) states that if accumulation of hazardous quantities of smoke in the cockpit area is reasonably probable, smoke evacuation must be readily accomplished, starting with full pressurization and without depressurizing beyond safe limits. This capability must be demonstrated for certification under 149
any normal operating condition, including unpressurized flight; and smoke clearance must be accomplished within three minutes (Advisory Circular 25-9A, or latest revision, explains a test procedure in detail). Section 25.831 also specifies limits for carbon dioxide and carbon monoxide, but does not define unsafe levels of any other gas, vapor, or fume. Since the toxicity of smoke or fumes generated by a fire is unknown, the FAA has required that there be essentially no penetration of smoke into an occupied compartment. Since it is likely that smoke of unknown composition would be generated within the cockpit, and may be present for up to three minutes prior to its removal, installation of protective breathing equipment would be appropriate, unless the applicant can show that it is not necessary.
(4) Definition of Terms Used in § 25.1439. The following policy was extracted from an FAA memorandum dated February 26, 1985, that responded to a request for the meaning of the words "isolated separate compartment," as used in § 25.1439.
(a) The preamble to the Notice 75-10, item 2-91, read: "The proposal would require protective breathing equipment for crewmembers expected in isolated areas." Item 2-91 was based on the First Biennial Airworthiness Review of 1974-1975, proposal No. 812 that read:
"(a) Protective breathing equipment must be installed for each required crewmember in isolated separate compartments, such as upper or lower lobe galleys, in which occupancy is permitted during flight."
(b) Based on the intent of the background quoted above, the FAA concluded that the crew rest area, not being part of the main cabin, is similar in location to a lower lobe galley and, therefore, is an isolated separate compartment. However, as crewmembers are not required in the crew rest area except to fight a fire, only sufficient protective breathing equipment need be provided in the crew rest area for that function. It is also noted that, as long as the lavatory is located next to the flight deck door, there is little chance that a crewmember may be isolated there by a fire. The crew lavatory need not be considered isolated.
e. References. The address for ordering the latest revision of the technical standard orders listed below can be found in the Appendix to this AC.
TSO-C99, Protective Breathing Equipment.
TSO-C116, Crewmember Protective Breathing Equipment.
63. SECTION 25.1441 - OXYGEN EQUIPMENT AND SUPPLY.
a. Rule Text.
(a) If certification with supplemental oxygen equipment is requested, the equipment must meet the requirements of this section and 25.1443 through
25.1453.
(b) The oxygen system must be free from hazards in itself, in its method of operation, and in its effect upon other components.
(c) There must be a means to allow the crew to readily determine, during flight, the quantity of oxygen available in each source of supply.
(d) The oxygen flow rate and the oxygen equipment for airplanes for which certification for operation above 40,000 feet is requested must be approved.
b. Intent of Rule. This rule is intended to ensure that, if supplemental oxygen equipment is to be included in the type design of an airplane, the oxygen dispensing equipment will protect passengers and crewmembers from the effects of hypoxia. Many of the oxygen system requirements are addressed in §§ 25.1443 through 25.1453, which are incorporated by reference.
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 section 4b.651(a) of the CAR for oxygen systems were carried over essentially unchanged to § 25.1441 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) Compliance with §§ 25.1309(c) and 25.1441(c). The following policy was extracted from an FAA memorandum dated February 23, 1994, and provides an FAA position on the requirements of § 25.1309(c) as related to a Passenger Gaseous Oxygen System that could erroneously indicate oxygen is available.
(a) 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." Section 25.1441(c) states: "There must be a means to allow the crew to readily determine, during flight, the quantity of oxygen 151
available in each source of supply." An applicant proposed a passenger oxygen system where the means is provided through an indication available to the flight crew of the oxygen pressure in the oxygen system plumbing between the oxygen bottles and the flow control valves. There are several bottles, each with its own shut-off valve, manifolded together. If, during maintenance, the valves on all the bottles are turned off and left in that position, but the tubing between the bottles and the flow control valve is not disturbed, the pressure in the lines will continue to read the same value that would be measured if the bottle valves were open. Therefore, the reading in the cockpit will erroneously indicate that oxygen is available. A concern arises because the flightcrew will dispatch believing that passenger oxygen is available. If a depressurization event occurs, the passengers will not have supplemental oxygen available as required by the regulations. Passengers will be at risk during the emergency descent due to lack of available oxygen.
(b) The non-availability of passenger supplemental oxygen presents a hazard if a depressurization occurs. In most cases of depressurization, the flightcrew executes an emergency descent and the cabin altitude does not exceed safe limits. This is not, of course, always the case; loss of consciousness or more serious injury, and even death, could occur for some passengers if oxygen is not available after depressurization. There is usually no risk to the airplane itself because the flightcrew has a separate oxygen system and, assuming they act properly, the airplane will quickly descend to a safe altitude and proceed to the nearest airport.
For these reasons, passenger supplemental oxygen being unavailable is not an immediate threat to continued safe flight and landing. However, one of the design principles suggested in Advisory Circular (AC) 25.1309-1A for ensuring fail-safe design concepts is error tolerance to allow for possible adverse effects of foreseeable errors during the airplane's design, test, manufacture, operation, and maintenance. This system does not appear to adhere to that principle. In addition, the AC also notes that a warning is required for a failure which makes it necessary for the flightcrew to make an unscheduled landing to reduce exposure to a more hazardous failure condition that would result from subsequent failures or operational conditions, or if the failure must be corrected before a subsequent flight. In conclusion, a warning to the flightcrew for non-availability of passenger oxygen is the type of warning addressed in the first sentence of § 25.1309(c).
(c) The system installed to provide the crew with an indication of the amount of oxygen available does not appear to meet the requirement contained in the second sentence of § 25.1309(c). The false indication of oxygen pressure resulting from the oxygen trapped between the shut off valves and the flow control valves will continue indefinitely, leading to dispatch after dispatch with no means to detect the problem until either a depressurization occurs or some maintenance action leads to the discovery that the oxygen bottle valves are closed. If the crew were aware of the situation, they would not dispatch or, if the problem were discovered in flight, they would immediately divert to an alternate airport. Clearly, the indication system is not designed to minimize crew errors that could create additional hazards.
(d) It is not acceptable to use probability of the event (depressurization) to demonstrate the probability of the unsafe condition (decompression combined with passenger oxygen being unavailable). In this case, the unsafe condition is not catastrophic so it is not 152
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