A new Sec. 91.32 would be added to the general operating rules of Part 91 to regulate the use of supplemental oxygen throughout the range of cabin altitudes and specify the oxygen supply to be carried, including the oxygen necessary for emergency descent. Supplemental oxygen refers to any oxygen, by whatever means supplied, that is furnished in addition to the oxygen normally present in the air.”
Amendment 23-9 is clarified by Final Rule, Docket 8281, as follows: “Several commentators objected to the proposal on the basis that it would require the owners of small airplanes that are not designed to operate at altitudes where oxygen is required to purchase expensive oxygen equipment for their airplanes. This, however is not the case. The proposal would not require the installation of oxygen equipment on all small airplanes. Oxygen equipment would have to be installed only on small airplanes that are to be used in operations conducted at the altitudes for which supplemental oxygen must be provided and used in accordance with the requirements of Part 91. The need for oxygen in such operations far outweighs any economic burden that may be involved in the installation and maintenance of the oxygen equipment.
Several commentators suggested revising proposed Sec. 23.1441(a) which states that there must be a means to allow the crew to readily determine during flight the quantity of oxygen available in each source of supply. It was recommended that the proposal be changed to specify a means for determining the remaining number of hours of available oxygen. These commentators are primarily concerned with the pressure gauges being furnished with oxygen systems. They believe that a pressure gauge is not an adequate instrument for determining the quantity of oxygen available.
The FAA does not agree. In most instances, a pressure gauge in the oxygen system will indicate the quantity of oxygen available in the source of supply. If, in any particular installation, it is determined that a pressure gauge would not satisfy the requirement, then some other means to allow the crew to determine, during flight, the quantity of oxygen available in each source of supply would have to be provided. In any event, the remaining number of hours of available oxygen can be readily obtained once the quantity of oxygen available in each source of supply is known.
In response to numerous comments, Sec. 23.1441 has been revised to make it clear that portable oxygen equipment may be used to meet the supplemental oxygen requirements.”
Plastic lines (nylon, PVC and Teflon) are not acceptable for use in continuously pressurized, non-portable oxygen systems.
Plastic lines can be used in non-portable oxygen systems that are pressurized only when cabin decompression occurs with the following precautions:
a. Swaged metal type end fittings should be used to prevent leakage from cold flow.
b. Lines should be protected from abrasion by use of a reinforcing sleeve of fabric braid.
c. Lines should be routed away from areas where they might be subjected to elevated temperatures, electrical arcing (relays and switches), and flammable fluids.
d. Refer to AC 43.13-2A, “Acceptable Methods, Techniques, and Practices⎯ Aircraft Alterations,” and American Society for Testing and Materials (ASTM) Manual 36, “Safe Use of Oxygen and Oxygen Systems, Guidelines for Oxygen System Design, Materials Selection, Operations, Storage, and Transportation”, dated 2000Chapter 6; for additional guidance material.
Design and install oxygen tubes/hoses in such a manner the hoses are stable during all phases of flight. It is not adequate to require the applicant to design tube/hose routings and chaffing protection without ensuring (by design) the installed tubes/hoses will not vibrate/flap in a manner that would either defeat the chaffing prevention wrap, or to impact other system elements such as sensors, wires, and mechanisms.
Part 23 is unique in that it allows oxygen system requirements to be met with portable systems. For those portable systems, information should be provided to the flight crew in the form of limitations stating which portable system is approved, which components constitute the system, and any operating limitations.
Part 23 airplanes may be certified with or without an oxygen system. The need for supplemental oxygen is a function of the operational altitude not the airplane design.
Therefore, the requirements for when supplemental oxygen is required can be found in General Operating and Flight Rules. If installed, the system should meet the following part 23 airworthiness requirements as follows: (a) §§ 23.1441 through
23.1449 (and § 23.1450 if chemical oxygen generators are used), and (b) it may be a basic part of the airplane or a portable system. Section 23.1525 requires the airplane operational limits be established in accordance with the installed equipment or lack.
If an airplane is delivered without an oxygen system, its AFM should have a limitation or there should be a placard prohibiting flight above 14,000 feet MSL.
Amendment 23-43 and Subsequent
Under the previous amendment, certification of an oxygen system was at the discretion of the applicant. Under this amendment, an oxygen system “must be provided” if an airplane is certificated to operate at altitudes where the operational rules require oxygen use. This rule is applicable to any airplane with a certification basis of Amendment 23-43 or later.
The rule allows portable systems to be designed by a TC holder subject to actions to prevent the portable system from being a hazard by not being properly secured in an emergency landing (according to § 23.561). The precise requirement for portable systems should be determined for the specifics of the airplane type (that is, its service ceiling and number of seats). The rulemaking history does not state a safety deficiency in current methods of providing supplemental oxygen by operatorprovided, portable, constant flow oxygen systems either attached to the seatback or restrained by a seatbelt.
If a TC holder does not plan to provide an oxygen system, it must specify a maximum weight and size of portable oxygen bottle and a specific means of restraining the bottle in an emergency landing according to § 23.561 either by attachment to a seatback or a seatbelt. This could be commercially available or produced by the TC holder and available with the airplane as standard equipment or as an option.
If an applicant does not provide the oxygen system or restraint information for portable bottles, the airplane will be limited to operational altitudes where oxygen is not required.
Amendment 23-43 added § 23.1441(e). It requires there be a means readily available to the flight crew to both turn ON and turn OFF the oxygen supply at the highpressure source. A flow fuse that senses a rupture in an oxygen line and automatically shuts off is not an ELOS to the required pilot operated switch since it only applies to one failure where oxygen shutoff is needed. It was made clear by the NPRM the switch was needed to turn ON and OFF the oxygen system, to shutoff if a rupture or fire occurs.
23.1443 Minimum mass flow of supplemental oxygen
There is no corresponding rule in CAR 3 or the Airship Design Criteria.
Original Issue and Subsequent
When there is full compliance to this regulation, there is no need to consider the likelihood of a pressurization failure or to require an immediate descent in altitude if a failure occurs. Compliance should include the consideration of a rapid explosive decompression to ambient pressure with a pilot recognition and reaction time of 17 seconds to initiate a descent.
(a) The airplane may be altitude-limited to meet this requirement, or
(b) The applicant may provide an ELOS finding.
Amendment 23-9 and Subsequent
A proposed revision to NPRM 67-30 explains this amendment as follows: “In connection with the standards for minimum mass flow of supplemental oxygen, the proposed Sec. 23.1443 contains requirements for continuous flow but not for demand flow oxygen equipment. The requirements of the more commonly used continuous flow systems are thus covered, while the mass flow of demand systems, where such systems are used, would be approved on a case-by-case basis as before.”
This amendment is clarified by Final Rule, Docket 8281, as follows: “One commentator suggested incorporating a provision in Sec. 23.1443 which would require compliance with the proposed graph (depicting oxygen mass flow rates) only up to the cruising altitude for which type certification of the airplane is desired. The recommendation is premised on the contention that it is unnecessary and economically unreasonable to install oxygen equipment capable of a specified mass flow rate at 40,000 feet if the airplane will be operated at a much lower altitude. The purpose of Sec. 23.1443 is to show the minimum oxygen mass flow rates which would be required for each occupant of an airplane at the corresponding cabin pressure altitudes. The applicant for a type certificate would not be required to install oxygen equipment capable of supplying the minimum oxygen mass flow rates for the entire range of cabin pressure altitudes shown in the graph unless his airplane is capable of operating through the entire range. Accordingly, Sec. 23.1443 is revised to state that the oxygen equipment installed in the airplane must be capable of supplying to each occupant the appropriate flow of oxygen for all altitudes up to and including the maximum operating altitude of the airplane.”
Amendment 23-43 and Subsequent
A proposed revision to NPRM 90-23 explains this amendment as follows: “This proposal modifies the oxygen flow rates for small airplanes. These new requirements are needed for current and future airplanes that will be certificated to higher altitudes where oxygen is required.
Conference proposal 472 recommended revising Section 23.1443 by designating the present paragraph as paragraph (a) and adding a new paragraph (b) to read essentially the same as Section 25.1443(b). The justification given was that "The oxygen flow rate requirements of parts 23 and 25 are different. However, both regulations provide requirements needed to ensure continuous flow rates up to cabin pressure altitudes of 40,000 feet. Proposed Section 23.1443 is a combination of these requirements. Proposed Section 23.1443(a) contains current Section 23.1443 with regard to continuous flow requirements, and Section 23.1443(b) is derived from Section 25.1443 for demand system requirements. The language of the recommended change would allow Section 23.1443 to cover both continuous flow oxygen and demand systems without interpretation from part 25."
“Conference proposal 473 recommended revising § 23.1443 essentially as shown in this proposal since the oxygen flow rate requirements of parts 23 and 25 are different. However, both regulations provide requirements needed to assure continuous flow rates up to cabin pressure altitudes of 40,000 feet. Proposed § 23.1443 is a combination of these requirements. Sections 23.1443 (a)(1) and (a)(2) contain the continuous flow requirements of part 25 and allow the applicant to comply with those requirements or with paragraph (a)(3), which is the current continuous flow requirement of part 23. Demonstrating compliance with proposed § 23.1443(a)(3) is easier, but results in a larger volume of oxygen and more weight.
Demonstrating compliance with § 23.1443 (a)(1) and (a)(2) is harder, but results in a lesser volume of oxygen. By allowing the applicant to choose either method of compliance, this requirement permits freedom of design.
When presented for comment at the conference, the FAA confirmed that this conference proposal would allow alternatives of continuous flow oxygen equipment or demand oxygen equipment. With a good face-fitting mask, less oxygen will be used with a demand system than with a continuous flow system. Studies on altitude sickness and the impairment of ability to function on continuous flow equipment at altitudes above 25,000 feet leads the FAA to reconsider this issue, especially for flight crews.
Proposed paragraph (c) provides the flow rate requirements for first-aid oxygen equipment if installed, but does not require its installation. These requirements are identical to the first-aid oxygen flow rate requirements in part 25. With the recent addition on commuter category airplanes in part 23, first-aid oxygen equipment is more likely to be installed in part 23 airplanes.
Proposed paragraph (d) is clarifying by providing definitions of the term "BTPS" and "STPD" as used in this section.
Post conference review of these comments and the oxygen requirements of parts 91, 121, and 135 led to the conclusion that (1) adding the equivalent of the part 25 oxygen requirements to part 23 will provide adequate protection for both flight crew and passengers; and (2) that crewmembers should have demand oxygen equipment for operations above 25,000 feet.”
This amendment is clarified by Final Rule, Docket 26344, as follows: “This proposes to amend Sec. 23.1443 to modify the oxygen flow rates for part 23 airplanes by providing alternate procedures that may be used to substantiate satisfactory continuous flow oxygen equipment. One commenter requested that the FAA make it clear that the 40,000 foot altitude limit in this proposal is not an absolute altitude limit for part 23 airplanes. The FAA agrees. The altitude limit in this proposal does not constitute an absolute altitude limit for the approval of part 23 airplanes;
however, the approval of individual airplanes would be limited to those altitudes where safe occupant protection is provided.”
23.1445 Oxygen distribution system
There is no corresponding rule in CAR 3 or the Airship Design Criteria.
Amendment 23-43 and Subsequent
A proposed revision to NPRM 90-23 explains this amendment as follows: “This proposal will establish standards for oxygen distribution systems not heretofore required. These requirements will prevent installation of plastic hoses in pressurized oxygen systems.
Conference proposal 474 recommended adopting equipment standards for oxygen systems essentially the same as proposed here. The justification given was that several accidents have occurred in airplanes where nylon tubing was used in an oxygen system pressurized to 70 psi. Because oxygen can support vigorous combustion, oxygen system installations warrant special attention in certification programs.
When presented for comment at the conference, the two commenters agreed that pressurized plastic tubing is inappropriate for oxygen system but did not completely agree with the proposal because they believed the rules should not specifically preclude all nonmetallic tubing. Some composite airplanes may need nonmetallic oxygen lines for lightning strike protection. In view of these comments, a phrase that allows a showing of suitability to the installation was added to the proposal.”
The guidance in this AC for § 23.1441, Amendment 23-9 and subsequent, for plastic lines is applicable to this regulation.
23.1447 Equipment standards for oxygen dispensing units
There is no corresponding rule in CAR 3 or the Airship Design Criteria.
Amendment 23-9 and Subsequent
This amendment is clarified by Final Rule, Docket 8281, as follows: “It was recommended that paragraphs (b) and (c) of proposed Sec. 23.1447 be revised to specify that they are applicable only to pressurized airplanes. The commentator asserts that these proposals should not apply to nonpressurized airplanes, which are not subject to sudden-decompression occurrences. The FAA agrees and this has been made clear in the final rule. In addition, further FAA studies have shown that for those pressurized aircraft designed to operate at 25,000 feet MSL or below, the pilot will have sufficient time to descend to safer altitudes prior to the onset of any symptoms of hypoxia in the event of a sudden decompression. For this reason, the proposal in paragraph (b) of Sec. 23.1447, requiring an oxygen supply terminal and unit of oxygen dispensing equipment within reach of each member of the required minimum flight crew for those airplanes designed to operate at flight altitudes up to and including 25,000 feet, is unnecessary and has not been adopted.”
The Small Airplane Directorate was recently asked for applicable policy about the requirements for (1) operation above 25,000 feet, dispensing units be immediately available to each occupant wherever seated, and for (2) operation above 30,000 feet, dispensing units be automatically presented to each occupant before the cabin pressure altitude exceeds 15,000 feet. Item (1) was incorporated into part 23 by Amendment 23-9 and item (2) above by Amendment 23-20. These rules were based on seats that were fixed in location and orientation. The question arises from the use of swiveling and tracked seats where it is possible for some occupants to move their seat into an orientation where an automatically presented dispensing unit will not be in view.
The following guidance is applicable to an airplane with a certification basis of Amendment 23-9 or subsequent. This guidance is taken from AC 25-17, section 25.1447, where the issue of tracked and swiveled seats has been addressed.
Automatic presentation is acceptable if the dispensing unit (mask) is presented in front of the eyes when the person's head is resting on the seat back cushion with the seat in any position, either as upright, reclined, swiveled or tracked. The mask need not be presented in front of all people if there is sufficient “crowd awareness,” that is, the vast majority has proper presentation and the others can readily see the masks have been presented. These latter people should have a preflight briefing clearly showing them the location of their mask. The mask should be reachable with the seat belt fastened. In some seating arrangements, such as executive interiors, the various seating positions result in many different group combinations. Each combination should have an adequate number of masks reachable by every person. Consideration 321
should be given to minimizing the likelihood of people taking the wrong masks, thus depriving another person of their mask. If the mask must be pulled to initiate oxygen flow, the mask should be presented so that the person must pull the mask to don it.
The fifth percentile female and ninety-fifth percentile male should be considered.
Either as sleeper seats, bunks or lavatories a streamer of webbing attached to the mask is acceptable to enable the person to pull the mask down to them.
Amendment 23-30 and Subsequent
A proposed revision to NPRM 75-23 explains this amendment as follows: “The proposal would require automatic presentation of oxygen dispensing units on airplanes certificated under Part 23 for operations above 30,000 feet. Should loss of pressurization occur at those altitudes, the time of useful consciousness varies between 90 seconds at 30,000 feet and 10-12 seconds at 40,000 feet, necessitating automatic presentation of oxygen dispensing units. It is also proposed to specify 14,000 feet as the cabin pressure altitude at which they must be automatically presented so that they would be ready for use not only when the cabin pressure altitude goes very rapidly to very high values but also in the event of a pressurization system failure or malfunction after which (under present Sec. 23.841(a)) the cabin pressure altitude may go to 15,000 feet. The 14,000-foot cabin pressure altitude for automatic presentation is also being proposed for Part 25.
In addition, since service experience has shown that the automatic presentation feature may fail, it is proposed that a manual means be provided to enable each occupant to gain access to his oxygen dispensing unit. This manual means is also being proposed for Part 25.”
This amendment is clarified by Final Rule, Docket 14625, as follows: “For comments related to the proposal to add new Secs. 23.1447(c) and (d), and for an explanation of the revisions made to proposed Secs. 23.1447(c) and (d), see Proposal
5-34. One commentator objected to the provision in proposed Section 25.1447(c)(1) which would require that oxygen dispensing units be automatically presented before the cabin pressure altitude exceeds 14,000 feet, contending that long-standing FAA policy has been that the altitude for automatic presentation should be 15,000 feet and service experience over the last 16 years has not shown a need to reduce that altitude. The commentator further stated that the flight crew is given a warning when or before the cabin pressure altitude reaches 10,000 feet and is therefore alerted (in the event of a gradual increase in cabin pressure altitude) to the need for appropriate action either to maintain a safe cabin pressure altitude or manually deploy the dispensing units. Another commentator suggested that the presentation altitude be 14,500 feet, rather than 14,000 feet, to take equipment tolerances into account.
In light of the comments received and after further review, the FAA believes that there is insufficient evidence at the present time to justify a requirement for the automatic presentation of oxygen dispensing units before the cabin pressure altitude exceeds 14,000 feet, and that the widely-used value of 15,000 feet provides an adequate level of safety. Proposed Section 25.1447(c)(1) is revised accordingly.
Several commentators disagreed with the provision in proposed Section
25.1447(c)(1) that would require that each occupant be provided with a manual means to make the oxygen dispensing unit immediately available, contending that manual back-up for the automatic presentation system should be provided for use by the crew only, to avoid tampering by the passengers. Another commentator stated that the average passenger would not be capable of operating such manual means properly and quickly, and that manual means are not feasible for ceiling or hatrack mounted dispensing units.
The FAA believes that a manual means must be provided to back up the automatic presentation system, but is persuaded that it may not be in the interest of safety to require that a manual means be provided for passengers. Accordingly, proposed Section 25.1447(c)(1) is revised to require only that a manual means for the development of the dispensing units be provided for the crew.”
Amendment 23-30 and Subsequent
This amendment allows the use of nasal cannulas for operation up to an altitude of 18,000 feet MSL. These are simple devices with no known service problems, and the FAA has not developed a design standard for them.
Section 23.1447(e) requires that oxygen masks be automatically presented to each occupant before the cabin pressure exceeds 15,000 feet for airplanes certificated for operation above 30,000 feet MSL. Before the cabin pressure altitude exceeds 15,000 feet, the oxygen mask should fall down automatically and present itself to a 95th percentile human occupant at mouth level within the visual periphery. All the occupant should have to do is pull the mask from the hanging position, don the mask, and start breathing.
Amendment 23-43 and Subsequent
A proposed revision to NPRM 90-23 explains this change to Amendment 23-43 as follows: “This proposal would add presentation requirements for the demand oxygen equipment required by Section 23.1441(d) and allow the option of quickdonning type oxygen dispensing units.”
Amendment 23-49 and Subsequent
A proposed revision to NPRM 94-21 explains this amendment as follows:
“Proposed new Sec. 23.1447(a)(4) would require that if radio equipment is installed in an airplane, flightcrew oxygen dispensing units must be designed to allow the use of communication equipment when oxygen is being used. If radio equipment is installed, that equipment cannot perform its intended function if the flightcrew is not provided the proper means for its utilization under all operating conditions, including operations when oxygen is being used.
This proposal would not require all flightcrew oxygen dispensing units to be equipped with communication equipment. Since an airplane may be operated in uncontrolled airspace, where two-way radio communication is not required and, at the same time, be at altitudes where oxygen is required for the flightcrew members, some airplanes have a crew oxygen system but no radio equipment. It would be inappropriate to require the flightcrew dispensing units of those airplanes to be equipped with communication equipment.
The proposed revisions to Sec. 23.1447(d) would require the flightcrew oxygen dispensing units to be automatically presented before the cabin pressure altitude exceeds 15,000 feet or be the quick-donning type if the airplane is certificated for operation above 25,000 feet. The requirement in paragraph (e) for the passenger dispensing units to be automatically presented if the airplane is approved for operation above 30,000 feet has not been revised. The revision to paragraph (d) would provide the flightcrew and the airplane passengers the same level of safety as provided by other airworthiness standards. This proposed revision is also consistent with the proposed revision of Sec. 23.841 in this notice.”
23.1449 Means for determining use of oxygen
No policy available as of September 30, 2003.
There is no corresponding rule in CAR 3 or the Airship Design Criteria.