Civil Aviation Order 108.26 - System specification - Oxygen systems (12/12/2004)

The Order introduces several technical concepts that are critical to understanding its operation. BTPD (body temperature and pressure dry), BTPS (body temperature and pressure saturated), and STPD (standard temperature and pressure dry) are standard physiological and engineering units used to define oxygen flow rates under different reference conditions. They matter because the minimum mass flow requirements in section 6 are expressed in these units, and an incorrect conversion could lead to an undersupply of oxygen in an emergency. Supplemental oxygen is oxygen provided to augment ambient air, as distinct from first-aid oxygen or protective oxygen. The Order distinguishes between continuous flow equipment, demand equipment, and portable oxygen units. Continuous flow supplies a constant stream; demand delivers oxygen only on inhalation; portable units can be moved. Each type has different minimum flow requirements (section 6). The dispensing unit is the mask or cannula that delivers oxygen to the occupant. The Order requires that each occupant have an individual unit and that, above flight level 180 (approximately 18,000 feet), every unit must cover the nose and mouth (paragraph 5.1.3). Below that, only one in 15 units needs to be a nose-and-mouth type (paragraph 5.1.2). This ratio reflects a cost-risk trade-off: at lower altitudes, hypoxia onset is slower, so not every passenger needs a full mask; but the operator must still ensure that enough masks are available for crew and for a sudden depressurisation. Protective breathing equipment (PBE) is a distinct category for smoke/fume protection, requiring eye coverage and a 15-minute oxygen supply. The Order specifies how to calculate that duration: for a demand system, 300 litres of free oxygen at 20°C and 760 mm Hg is deemed equivalent to 15 minutes at a respiratory minute volume of 30 L/min BTPD at sea level. This is a regulatory fiction that simplifies compliance but may not perfectly match real physiology. Mean tracheal oxygen partial pressure is the physiological target. For crew on continuous flow equipment, it must be at least 149 mm Hg (paragraph 6.1); for demand equipment, 122 mm Hg up to 35,000 feet and 95% oxygen between 35,000 and 40,000 feet (paragraph 6.2). These targets are derived from aviation medicine standards and are not to be adjusted by the operator. The Order also introduces the concept of system arrangement, allowing portable oxygen units to meet crew or passenger requirements (paragraph 4.3). This provides flexibility but places the onus on the operator to ensure sufficient portable units are carried, stowed, and accessible. The Oxymizer exception is notable because it is a specific brand and model: “nasal cannula manufactured under the name ‘Oxymizer’”. This is unusual for a performance-based regulation; it suggests the regulator accepted a particular product’s test data. Any operator wishing to use a different cannula would need separate approval, which may not be forthcoming if CASA has already endorsed only this brand.

The Order directly affects any person or organisation that operates an Australian aircraft with an oxygen system required by CASA or an authorised person under the Civil Aviation Regulations. That includes commercial airlines, charter operators, aerial work operators (e.g., survey, spotting, agriculture), flight training schools, and private owners of pressurised or high-altitude aircraft. It also affects the crew members who must use the equipment: flight crew, cabin attendants, and passengers (though passengers are not individually regulated, the operator must provide compliant equipment for them). Maintenance organisations and approved persons who install, repair, or test oxygen systems are affected because they must use only oxygen sources from the acceptable specifications list (section 3) and must ensure dispensing units meet the labelling requirements (paragraph 5.1.6) and that flow rates are achievable with the installed equipment. Manufacturers and importers of oxygen components are indirectly affected: to sell into the Australian market, their products must either appear on the acceptable specifications list or receive separate CASA acceptance. This creates a barrier to entry for small or foreign manufacturers not already on the list (e.g., RAAF G172, U.K. DEF STAN 68-2, U.S. MIL-O-27210). The Order also affects CASA itself, which must adjudicate on the acceptability of alternative oxygen sources and approve quick-donning mask demonstrations. The compliance burden is not uniform: operators of unpressurised aircraft face a phased timetable for retrofitting dispensing units with smoking prohibition notices, donning illustrations, and nasal obstruction warnings (paragraphs 5.1.4 and 5.1.5). Those operating above flight level 180 must replace all existing units that do not cover nose and mouth; that is a capital cost. Operators above 25,000 feet face the highest compliance burden: they must install at least 10% more dispensing units and outlets than seats, uniformly distributed (paragraph 5.3(a)); provide demand equipment for flight deck crew; demonstrate quick-donning mask performance to CASA; and provide portable oxygen for each cabin attendant (paragraph 5.3(d)). These requirements apply to all operators in that altitude band, regardless of the aircraft’s age or the operator’s financial capacity. Private pilots operating unpressurised aircraft below flight level 180 may be affected only if CASA has separately required oxygen; but if they carry passengers, they must still provide the required number of nose-and-mouth masks per paragraph 5.1.2. The Oxymizer exception specifically targets private, aerial work, or charter operations. This limits the class of eligible operators and excludes commercial air transport (regular public transport). So a charter operator can use a cheaper cannula for its crew, but an airline cannot. That differential may distort competition in the small-aircraft market.

The Order imposes several duties on the operator (or the person responsible for the aircraft). The primary duty is to ensure that any oxygen system installed complies with the specifications in this Order when required by CASA or an authorised person under the Civil Aviation Regulations. The Order does not itself mandate when oxygen must be used; it is a specification order, not an operational order. However, once oxygen is required, the operator must ensure that the oxygen source is from the acceptable list (section 3), that each occupant has a dispensing unit (paragraph 5.1), that the units meet the anatomical coverage requirements (nose and mouth above FL180, ratio below), and that for crew, the appropriate flow rates are achieved (section 6). For operations above 25,000 feet, additional duties arise: the operator must install extra dispensing units (10% over seat count, uniformly distributed), provide demand equipment for flight deck crew, and demonstrate to CASA’s satisfaction that quick-donning masks can be donned within 5 seconds with one hand, without disturbing eyeglasses, and that communication is possible immediately (paragraph 5.3(b)(i)-(iii)). The operator also has a duty to provide portable oxygen equipment for each cabin attendant (paragraph 5.3(d)) and protective breathing equipment for flight crew covering eyes and supplying oxygen for 15 minutes (section 7). The operator must ensure that protective breathing equipment does not impair vision or prevent radio communication. A significant right of the operator is the ability to use portable oxygen units to meet crew or passenger breathing requirements (paragraph 4.3). This permits flexibility; an operator is not forced to have fixed oxygen outlets for all seats if portable units can be stowed and deployed. Another right is the ability to use the specified flow rates and mask efficiencies in Appendix II as an alternative to the physiological computation in paragraphs 6.1 and 6.3. The Appendix provides a table of minimum flow rates for masks with efficiencies equal to or better than the A8B oronasal mask, Scott 28302-11, or K-S disposable mask. This is a safe harbour: if the operator uses one of those masks and provides the listed flow rates at each cabin altitude, compliance is presumed without further physiological testing. Flight crew have a right to use the Oxymizer nasal cannula under the conditions of paragraph 6.1A, but that right is limited to private, aerial work, or charter operations below 18,000 feet. Crew also have a right to undiluted oxygen at their discretion when using demand equipment (paragraph 6.2). The operator has no right to deviate from the specifications without CASA approval; there is no self-certification pathway except where the Order expressly allows use of Appendix II or the Oxymizer. CASA has the right to accept or reject alternative oxygen sources and to be satisfied of quick-donning mask performance.

The Order itself does not prescribe penalties. It is a legislative instrument made under the Civil Aviation Regulations 1988, and enforcement flows from the parent regulations and the Civil Aviation Act 1988. Under regulation 207 of CAR 1988, a person must comply with a Civil Aviation Order; contravention is an offence. Typically, the maximum penalty is 50 penalty units (currently $313 per unit, so up to $15,650) for an individual, and higher for a body corporate under the Acts Interpretation Act. However, the Order does not specify these penalties, so a reader must look to the parent legislation. The practical enforcement mechanism is through CASA’s regulatory oversight: inspectors may check oxygen systems during airworthiness reviews, ramp inspections, or following an incident. Failure to have compliant dispensing units or adequate oxygen supply could ground the aircraft or lead to suspension of the air operator’s certificate. The demonstration requirement under paragraph 5.3(b) (quick-donning mask) is enforced by CASA’s refusal to accept the system. If an operator cannot demonstrate the 5-second donning, the aircraft cannot operate above 25,000 feet with that mask configuration. The Order also imposes a temporal duty: for unpressurised aircraft, units installed after 10 January 1996 must have the smoking prohibition, donning illustration, and nasal obstruction warning; from 10 January 1999, all units must meet that requirement (paragraphs 5.1.4 and 5.1.5). An operator that fails to retrofit older units after that date would be in breach. The Oxymizer exception is conditional; using a cannula outside the specified operations (e.g., in regular public transport) or above 18,000 feet would be a breach of paragraph 6.1A. The Order does not provide for any administrative appeals procedure within its text; non-compliance would be dealt with under the CAR enforcement framework, which includes infringement notices, enforceable undertakings, and court proceedings. The cost of penalties may be small compared to the cost of retrofitting aircraft, but the reputational and operational risk of an airworthiness directive or grounding is significant. Prosecutions are rare for purely technical non-compliance unless there is a causal link to an accident. The Order creates a regime where strict compliance is expected, but the ambiguity in “acceptable to CASA” (section 3) gives CASA discretionary power. An operator could face enforcement if CASA later decides a previously acceptable oxygen source is no longer acceptable. There is no grandfathering clause in the Order (except the phased labelling requirements); changes to the acceptable list could render existing equipment non-compliant.

This Order is one of many Civil Aviation Orders made under the Civil Aviation Regulations 1988. It sits within a broader regulatory framework that includes the Civil Aviation Act 1988 and the Air Navigation Act 1920. Its immediate parent is subregulations 207(2) and (3) of CAR 1988. It must be read in conjunction with other CAOs that mandate when oxygen must be used, most notably CAO 20.4, which is referenced in paragraphs 5.2 and 5.3 of this Order. CAO 20.4 sets the altitude triggers and durations for oxygen use; this Order provides the technical specifications for the systems that must be provided when those triggers are met. For example, paragraph 5.2 says that for operations up to 25,000 feet where section 20.4 requires oxygen, each crew member must have a readily available oxygen supply terminal and dispensing unit. So the interaction is: CAO 20.4 creates the duty to have oxygen; CAO 108.26 defines the equipment standard. The Order also interacts with airworthiness regulations under Part 21 of CASR (Civil Aviation Safety Regulations) and with maintenance regulations under Part 145 or Part 42. The specifications for oxygen sources (section 3) refer to military and commercial standards; the Order does not incorporate those standards in full text, so an operator must obtain those standards separately. This creates a cross-reference compliance cost: the operator must own or have access to RAAF G172, DEF STAN 68-2, etc., to verify that their oxygen supply meets the specification. The Order has a specific provision for operations above 40,000 feet: the note to paragraph 1.1 states that specifications for altitudes above 40,000 feet are subject to separate determination by CASA. So this Order does not apply above that altitude; operators of high-altitude business jets or U-class aircraft must look to other instruments. The Order does not purport to override state or territory workplace health and safety laws, but in practice, CASA’s regulatory scheme prevails for aircraft in operation. The interaction with international standards is indirect: the Order accepts UK, US, and Australian Defence Force standards for oxygen purity, but does not adopt EASA or FAA standards wholesale. This may create friction for operators importing aircraft from Europe or the US; they must ensure their oxygen systems meet the Australian acceptable list, which may require requalification. The Order also interacts with the Australian Dangerous Goods Code for transport of oxygen cylinders, but that is outside the scope. The Oxymizer exception may conflict with other CAOs that require full face masks for crew; but this Order carves out a specific exemption only within its scope. There is no explicit reference to privacy or data protection; this is a purely technical standard.

The compilation shows that the current text of CAO 108.26 was made by CAO 2004 No. R95, notified on 23 December 2004 and commencing on that date. This replaced a previous version entirely (the table says “rs. CAO 2004 No. R95”, meaning repealed and substituted). The only amendment since then is CAO 108.26 Amendment Order (No. 1) 2007, which was registered on the Federal Register of Legislative Instruments on 2 November 2007 and commenced the next day, 3 November 2007. That amendment affected subsection 6 only (the table shows “subs. 6” was amended by that order). Subsection 6 deals with minimum mass flow of supplemental oxygen. It is likely that the 2007 amendment added paragraph 6.1A (the Oxymizer exception) or adjusted the flow rates in paragraph 6.3.1 or 6.4. The notes to the compilation indicate that the compilation was prepared on 2 November 2007, so the amendment is included. The original CAO 108.26 before 2004 would have been an earlier version; the 2004 substitution likely overhauled the order to align with contemporary aircraft technology and physiological standards. There are no further amendments listed, meaning this instrument has been static since 2007. This is notable because aircraft technology and oxygen systems have evolved (e.g., electronic oxygen conserving devices, newer mask designs). The absence of update may indicate regulatory inertia, leaving operators to seek CASA approval for new technologies on a case-by-case basis. The amendment history does not include any application, saving, or transitional provisions for either the 2004 or 2007 instruments (the table notes “Application, saving or transitional provisions” columns are blank). That means the changes were likely straightforward substitutions with no grace period for existing installations, except for the phased labelling requirements that are built into the original 2004 text (paragraphs 5.1.4 and 5.1.5). The 2007 amendment appears to have been minor, as it only touched subsection 6. An operator relying on previous flow rate regimes would need to have updated compliance by 3 November 2007. Since then, no further amendments, so the instrument is now 16 years old. This creates a risk that the specifications are outdated or that CASA has issued separate guidance outside the formal amendment process (e.g., via Advisory Circulars). The lack of amendment history means that any later policy changes (e.g., acceptance of new oxygen standards) may not be reflected in the Order itself, creating a gap between the black-letter law and CASA’s operational practice.

The Order itself does not reference any litigation, and there is no mention of court cases in the source text. The compilation is a legislative instrument prepared by CASA’s Legal Services Group; it is not a reporter of judicial decisions. Therefore, a user cannot identify any case law from this instrument alone. However, it is possible that the parent regulations or the Civil Aviation Act have been litigated, but that is outside the scope of this Order. The Order’s technical nature makes it unlikely to be directly challenged in court; disputes over compliance are more likely to occur in administrative law (e.g., judicial review of CASA’s decision to accept or reject an alternative oxygen source under section 3 or of a demonstration under paragraph 5.3(b)). The lack of published decisions suggests either that the Order has not been contentious or that disputes have been resolved through CASA’s internal review processes without reaching a court. The Order’s specificity may also reduce litigation risk: the requirements are objective (flow rates, percentages, distances) leaving little room for interpretation. The main interpretative ambiguity is the phrase “acceptable to CASA”. That could be litigated if CASA unreasonably withholds acceptance, but the applicant would bear a heavy onus. There is also a potential for tort liability if an oxygen system fails due to non-compliance, but that claim would sound in negligence or product liability, not directly under this Order. The Order may be tendered as evidence of the applicable standard of care in a civil suit. No litigation history is identifiable from the source, so a researcher would need to search external databases such as AustLII or Westlaw for decisions referencing “Civil Aviation Order 108.26” or “oxygen systems”. The absence of reported cases may also indicate that operators generally comply, or that CASA uses administrative remedies rather than prosecution. However, the compliance burden is such that small operators might cut corners, and if an accident occurs, the Order becomes central. For now, the deep dive must report that the source lists no litigation history.

Several less obvious aspects of this Order can trap unwary operators. First, the application paragraph (1.1) states that the Order applies “in such circumstances as may be specified by CASA or an authorised person under the Civil Aviation Regulations 1988.” This means the Order is not self-executing. It only applies when another instrument triggers it. An operator might mistakenly believe they need to comply with this Order for all aircraft that carry an oxygen bottle, but if CASA has not specified the circumstances, the Order may not be mandatory. However, it is prudent to comply anyway because CAO 20.4 and other operational rules will invariably trigger the requirement for oxygen at certain altitudes. Second, the use of “must” throughout suggests strict duties, but some provisions allow alternatives. For example, paragraph 5.1.1 requires that a dispensing unit “must not adversely affect a person’s ability to use the aircraft’s electronic communication equipment while using the unit; or must provide alternative electronic communication equipment.” The word “or” means the operator can choose to provide alternative comms equipment instead of ensuring the mask is compatible. This could be a costly choice if not planned. Third, the footnote to paragraph 5.2 cross-references “section 20.4 of the Civil Aviation Orders.” There is no “section 20.4” in this Order; it is another CAO. An operator must retrieve that separate instrument to understand the full obligation. Fourth, the Appendix II reference in paragraphs 6.1 and 6.3 says “the flow rates and mask efficiencies in Appendix II may be used instead of the above flow rates.” Appendix II is a table that is printed in the Order but is not fully legible in the source (it shows an image placeholder). The table lists minimum oxygen flow rates for flight altitudes not exceeding 25,000 feet for specific mask types. An operator cannot rely on that Appendix if they cannot read the values; they must obtain the official Gazette version. Fifth, the Oxymizer exception (paragraph 6.1A and 6.3.1) is conditional on the cannula being “manufactured under the name ‘Oxymizer’”. Using a generic equivalent or a newer design could be non-compliant, even if physiologically identical. The operator bears the risk of verifying the exact brand. Sixth, the protective breathing equipment duration calculation in paragraph 7.5 uses “300 litres of free oxygen at 20°C and 760 mm Hg pressure is considered to be of 15 minute duration.” This is a regulatory assumption that may not hold at actual altitude or with a different breathing pattern. Operators who rely on that rule must ensure the oxygen cylinder contains exactly that volume, accounting for compressibility. Seventh, the paragraph 5.1.6 labelling requirements for dispensing units in unpressurised aircraft apply from a specific date, but there is no explicit exception for historic aircraft or foreign-registered aircraft operating in Australia. The dates are now long past (1996, 1999), so all units should already comply, but if an operator introduces an old aircraft from overseas, they must retrofit. Eighth, the Order does not specify the qualifications of the person who must demonstrate the quick-donning mask to CASA (paragraph 5.3(b)). It says “it must be demonstrated to the satisfaction of CASA.” CASA could require a design engineer test, or a company test, or an actual flight crew demonstration. The cost and complexity of that demonstration is not defined. Finally, the Order has no sunset clause or periodic review requirement. It may remain in force indefinitely, even as best practices evolve. Operators should not assume that compliance with this Order alone satisfies all oxygen system regulatory requirements; they must also comply with airworthiness directives and CASA’s additional guidance.

Compliance with CAO 108.26 is a layered process that begins with identifying whether the aircraft’s operations trigger the Order (step one). If the aircraft operates at altitudes above 10,000 feet or in any configuration where CASA or an authorised person has mandated oxygen under CAO 20.4 or another instrument, then this Order applies. For a typical pressurised aircraft operating above 25,000 feet, the operator must take the following steps. Step two: determine the appropriate oxygen source. Select gaseous oxygen complying with one of the accepted specifications in section 3.1 (e.g., CIG Gas Code 420 or MIL-O-27210) or use an oxygen generator meeting MIL-E-83252. Ordering oxygen from a supplier that can certify to one of these standards is critical. Step three: ensure each occupant has an individual dispensing unit. For flight crew, ensure units are supplied from a terminal that is readily accessible. For operations above FL180, every dispensing unit must cover the nose and mouth (paragraph 5.1.3). Below FL180, at least one unit per 15 must be nose-and-mouth type, and the rest can be less restrictive (e.g., cannula or simple mask). Check that units in unpressurised aircraft have the required labels (smoking prohibition, donning illustration, nasal obstruction warning) as per paragraph 5.1.6. Step four: for flight crew, verify the minimum mass flow rates. Use either the physiological computation in paragraph 6.1 or the safe harbour in Appendix II if using an approved mask (e.g., A8B oronasal mask). For the Appendix II route, consult the table (which gives flow rates in litres per minute at various cabin altitudes) and ensure the oxygen system can deliver those flows continuously. For the Oxymizer cannula, ensure compliance with paragraph 6.1A: private/aerial work/charter only; altitude not above 18,000 feet; flow rates per 6.1A(a). Step five: if operating above 25,000 feet, perform the additional design checks: install at least 10% more outlets and units than seats (paragraph 5.3(a)); ensure flight deck crew have demand equipment (paragraph 5.3(b)); arrange a demonstration to CASA that the quick-donning mask can be donned within 5 seconds with one hand without disturbing eyeglasses and with immediate communication (paragraph 5.3(b)(i)-(iii)). This may involve hiring a test pilot or medical expert and submitting a report. Provide portable oxygen for each cabin attendant (paragraph 5.3(d)). Step six: install protective breathing equipment for flight crew if the aircraft may encounter smoke or toxic fumes (section 7). The equipment must cover eyes or provide accessory eye coverage, supply 15 minutes of oxygen at 30 L/min BTPD, and allow radio communication. Check that the oxygen supply volume meets the deemed duration (300 litres free oxygen for demand, 600 litres for continuous flow). Step seven: for first-aid oxygen if installed, set flow to at least 4 L/min STPD, with means to reduce to 2 L/min (paragraph 6.4). Step eight: document compliance. Retain copies of the oxygen source certificates, mask specifications, demonstration reports, and maintenance records. Update the aircraft’s weight and balance records if portable oxygen units are carried. Step nine: on each flight, ensure crew are trained on the specific equipment and that pre-flight checks confirm oxygen supply quantities, mask function, and label legibility. Step ten: regularly review CASA’s publications for any Advisory Circulars that may supplement or interpret this Order, since the Order has not been amended since 2007 and CASA may have issued non-legislative guidance. If in doubt about any specification, apply to CASA for a determination or acceptance of an alternative. Given the strict liability nature of regulation 207, the safest approach is to follow the literal text and keep a clear audit trail.