AC 29-2C, Chg 4 2/27/2014 and so forth. Release devices that ar e simple and obvious and do not require exceptional effort are recommended. For ex ample, a single central control for litter release would be preferred over multiple action release devices. However, seats and litters that require multiple actions to release or reposition may be acceptable if properly evaluated to determine that, in the event of an emergency landing, there is no obstruction or delay if rapid evacuation is necessary.
(ii) The passenger compartment or cabin should not be partitioned to impede access to the exits. A person seated in the compartment should have access to each exit in the compartment. All persons must be able or have provisions to rapidly clear (evacuate) the rotorcraft (see § 29.803(a)). A demonstrati on or a “walk-through” of appropriate evacuation procedures may be necessary to ensure the means and procedures are feasible and adequate.
(iii) When an evacuation demonstration is determined to be appropriate for compliance, 90 seconds should be used as the time interval for evacuation of the rotorcraft. Attendants and the flightcrew, trained in the evacuation procedures, may be used to remove the litter patients. It is preferable for the pati ent to remain in the litter;
however, the patient may be removed from the litter to facilitate rapid evacuation through the exit. The patients are not ambul atory during the demonstration. Evacuation procedures should be included if isolettes are part of the interior. The demonstration may be conducted in daylight with the dark of the night simulated and the rotorcraft in a normal attitude with the landing gear extended. For the pur pose of the demonstration, exits on one side (critical side) should be used. Exits on the opposite side are blocked and not accessible for the demonstration. This is representative of a rollover or exits blocked due to a fire.
(iv) Special evacuation procedures and trained attendants may not be required for simple and obvious means of evacuation for a single litter. Procedures may be prominently displayed in durable markings, placards, cards, and condensed or summarized in the emergency procedures section of the Rotorcraft Flight Manual (RFM) or an EMS configuration RFM supplement.
(v) If any medical attendants are required for evacuation, the attendants should be trained in these procedures and listed in the limitations section of the RFM. If attendants are not essential for safe rotorcraft operation or rapid evacuation, then an attendant is not a required “crewmember.”
(3) Restraint of Occupants and Equipment. The emergency landing conditions specified in § 29.561(b) dictate the design load conditions. See AC 29-2, sections 29.561 and 29.785 for further information.
(i) Whether seated or recumbent, the occupants must be protected from serious head injury as prescribed in § 29.785. Swivel seats and tilt litters may be used provided they are substantiated for the appropriate loads for the position selected for approval. Placards or markings may be us ed to ensure proper orientation for flight, Page MG 6 - 4
takeoff, or landing and emergency landing conditions. The seats and litters should be listed in the type design data for the configuration. See paragraph b.(17) for substitutions.
(ii) For recumbent occupants, harnesses, straps, a padded headboard, a diaphragm, or safety belts may be used if in compliance with the load requirements of § 29.561(b) and § 29.785(k). Ha rnesses or straps are recommended. When used, they should prevent the occupant from significant forward motion in order to reduce occupant injuries. Infants in isolettes should be similarly protected by padding and containment within the isolette and the isolette restrained for the load cases noted in this paragraph.
If the infant is strapped to a removable platform, there should be proper restraint of the platform and infant within the isolette for the load cases noted in this paragraph. Isolette materials are also subject to the flammability standards noted in paragraph b.(4). The litter(s) and isolette(s) should be listed in the type design data for the EMS configuration.
(iii) An isolette used for the transport of infants presents a special case, in that it may be included as part of an approved EMS configuration or it may be carried on the rotorcraft as needed for transport of infants. If the isolette is self-contained and is not part of an approved EMS type design, it may be considered a carry-on item and not part of the EMS type design. In t hese cases, there is typically a means to position the carryon isolette and properly restrain the isolette for transport as part of the EMS design configuration.
(A) When the isolette is carry-on equipment, the operator must ensure that the isolette does not create a safety risk or interfere with aircraft operations. AC 135-14, Emergency Medical Services/Helicopter (EMS/H), provides information and guidance to air ambulance and EMS/H operators for large carry-on medical equipment such as isolettes. AC 135-14 includes the provision that isolettes are to be restrained in an appropriate manner and evaluated for specific emergency landing load factors as required by earlier amendments of the rotorcraft regulatory requirements. Since publication of AC 135-14. the emergency landing load requirements have changed for rotorcraft. Consequently; t he load factors specified in that AC may not be appropriate for rotorcraft, depending on the rotorcraft certification basis amendment level of the airworthiness standards. The minimum load factors should be no less than those specified in the certification basis of the rotorcraft transporting the medical equipment, such as isolettes.
(B) A placard indicating that the isolette should be evaluated per the guidance contained in AC 135-14 and restrained to the emergency landing load factors for rotorcraft occupants per 14 CFR 29.561(b)(3) or the appropriate reference based on the certification basis of the rotorcraft, should be placed in close proximity to the isolette mount location.
(iv) Galleys, medical supplies, and equipment compartments or modules should be restrained and the individual compartments must also contain the contents for Page MG 6 - 5
AC 29-2C, Chg 4 2/27/2014 the conditions noted in paragraph b.(3) of this guidance. Durable placards, decals, or markings should be used where appropriate to limit the maximum weight of any compartment and the whole module. Compartment latches having sufficient strength and displacement or engagement should be used to contain the contents for the conditions noted in paragraph b.(3) of this guidance. If necessary, a static load test or analysis should be employed to ensure the container or compartment remains intact and the latch does not disengage for the most critical conditions. Loose or unrestrained contents in an individual compartment, in combination with similar compartments, should require a magnification factor with the design conditions. Prudent design and location of compartments having heavy, unrestrained (loose) equipment will mitigate the potential effects of landing impact loads.
(4) Flammability of Materials. Interior materials must meet the flammability standards appropriate for the rotorcraft type design in § 29.853.
(i) For rotorcraft certified prior to adoption of Amendment 29-17 (1978), the cabin materials must be at least flash resistant and wall, ceiling linings, the covering of all upholstery, floors, and furnishings must be at least flame resistant. AC 23–2, Flammability Tests, contains test information about flash and flame-resistant material.
(A) Flash-resistant material may be characterized as that not exceeding a 20-inch-per-minute (horizontal) burn rate. See AC 23-2, Flammability Tests, for further information.
(B) Flame-resistant material may be characterized as that not exceeding a 4-inch-per-minute (horizontal) burn rate.
(ii) For rotorcraft certified to Amendment 29-17 adopted in 1978, the materials must be self-extinguishing as specified in the standards. For example, transparencies must be self-extinguishing as prescribed in § 29.853(a)(2).
(iii) Additionally, for rotorcraft certified to standards of Amendment 29-23 (1984), cushions of each passenger seat must have a “fire blocking layer” as prescribed in § 29.853(b).
(iv) When the isolette is included in the EMS configuration approval, the isolette materials are subject to the flammability standards of § 29.853. The current standards require that all materials, including transparencies, fabric (e.g., padding, covers), straps, etc., be self-extinguishing for each compartment used by crew or passengers.
(v)The applicant is urged to use self-extinguishing materials regardless of the certification basis.
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(vi) For further information on materials, refer to AC 29-2, section 29.853.
AC 23-2 also contains information about flash-resistant and flame-resistant material tests.
(5) . The approved exits require signs and Exit Signs or Markings and External Markings markings (instructions) for prompt evacuation even in darkness. The rotorcraft type design contains the required data. The maintenance manual and the RFM should also contain this information. See AC 29-2, section 29.811 for more information. Alternates may be approved, which then become part of the applicant’s type design data. All U.S. transport roto rcraft presently in service should have an emergency interior lighting system to comply with § 29.811(f). (Refer to the certification basis of the rotorcraft.)
(6) Interior or “Medical” Lights. The view of the fli ghtcrew must be free from glare and reflections that could cause interference. Use of a night vision imaging system (NVIS) should be a consideration in this evaluation. Curtains t hat meet flammability standards may be used. Complete partition or separation of the crew and passenger compartment is not prudent. Means for vi sual and oral communication are usually necessary. Refer to AC 29-2, section 29.773, which concerns pilot visibility.
(7) Patient Interference. When passengers or patients are located in close proximity to the pilot and the primary flight controls of the rotorcraft, a guard or shield should be installed, or the patient should be restrained to prevent inadvertent or potential patient interference with safe operation of the rotorcraft. The guard may be a part of the rotorcraft interior features. In addition, prompt evacuation should be ensured if a guard is used.
(8) External Devices.
(i) Search lights, loud speakers, baggage pods, etc., may be installed on the underside of or elsewhere on the rotorcraft. The strength of the attachments must be substantiated for the flight and landing conditions. The light s and the reflection from the lights should not adversely affect pilot view or visibility. Use of NVIS should be a consideration in this evaluation.
(ii) The device or pod located on the underside of the rotorcraft should not contact a level landing surface after “limit landing load” deflection of the landing gear.
The gear should deflect without causing damage to the device. For example, if the limit landing load deflection is 8 inches, the device would need to have at least 8-inch clearance to avoid contact with the landing surface or have an equivalent feature of design. The physical characteristics of the rotorcraft design dictate the necessary clearance for landing gear deflection. In addition, the device should be designed and located on the rotorcraft to preclude penetration of the device into a critical area of the fuselage. For example, the device should be located to minimize the potential of penetration into a fuel line, fuel cell, primary control tube, or occupant seat for any reason.
Page MG 6 - 7
AC 29-2C, Chg 4 2/27/2014
(iii) A flight evaluation is necessary to determine the effects of the device on the rotorcraft flight characteristics and on flight crew visibility. In addition, recent service history has shown that external equipment and external fixture modifications can affect main rotor mast bending loads. In lieu of a mast bending survey, a pre and post modification flight test may be conducted at the same gross weights, center-of-gravity (CG), power, and density altitude to compare a critical control position parameter (typically longitudinal cyclic stick position) at pre and post modification Vne airspeeds.
(A) If required, the post modification Vne should be reduced so that the post modification longitudinal cyclic stick position is slightly aft of (or less than) the pre modification stick position. This alte rnative procedure assumes that the static longitudinal stability of the helicopter has not been altered by the modification. For helicopters with neutral static stability, a more comprehensive investigation may be required.
(B) In some cases, a control position parameter other than longitudinal stick position may be critical. For example, a heavy external device mounted to the side of the helicopter that gives a lateral CG close to the limit and an asymmetric yaw component would require pre and post modification lateral cyclic stick and pedal position measurements. Operating limitations other than Vne may need to be established, or reduced from pre modification limitations, to ensure pre-modification mast bending is not exceeded.
(9) Miscellaneous. Various paragraphs in this MG contain guidance for the standards cited in the reference list (paragraph c.(1)). These paragraphs should provide insight into designing an EMS configuration that would be acceptable under the standards.
(10) Oxygen. EMS oxygen installations are supplied by either liquid or gaseous oxygen. Both types of systems are discussed in this paragraph.
(i) Liquid Oxygen.
(A) System General Description. Most liquid oxygen systems in use are installed in military aircraft and, as a result, much of this material is based on experience with these systems. A rotorc raft liquid oxygen system should be comprised of a liquid oxygen converter, tubing, fittings, quantity gage, heat exchangers, and appropriate pressure and flow control components as shown in figures AC 29 MG 6-1 and AC 29 MG 6-2. The installation may provi de for replenishing the liquid oxygen supply by use of a quick-removable converter or, in the case of a fixed installation converter, by providing external access for connection to a portable service trailer. More complicated systems such as those with multiple converter assemblies are not discussed here since installation of those systems are not envisioned in rotorcraft at this time.
Page MG 6 - 8
(B) suitable for use in an EMS rotorcraft application.
(1) Liquid Oxygen Converter. A liquid oxygen converter assembly is a self-powered system for the storage of liquid oxygen and for its conversion to gaseous oxygen when required. A principal part of the converter assembly is a vacuum insulated container. Pressure relief valves shoul d be provided to allow the escape of gas generated when oxygen is not being expended in the supply line. Oxygen losses from a converter assembly vary from 5 to 20 percent per 24 hours depending on the size of the container, its installation environment, and so forth. Ai rcraft qualified and approved converters suitable for EMS rotorcraft use are available in either 5 or 50-liter capacities.
Size selection should be determined by flow rate and duration requirements.
Performance characteristics of each converter size are available from the manufacturer.
(2) Shutoff Valve Assembly. This valve must be accessible to a flightcrew member and be mounted in the supply line on or as close as possible to the outlet of the converter. This valve provides for the confinement of the remaining supply of liquid oxygen to the converter in the event of an emergency. Since the system pressure is low, the use of an electrically actuated shutoff valve is satisfactory to accomplish this function. In some in stallations, where the evaporating coil is immediately adjacent to the converter, a flow fuse has been used to accomplish this function. Use of a flow fuse must be suppor ted by a system fault analysis and testing to show maximum normal flow will not result in nuisance trips, and reliable trips will be provided for malfunction conditions resulting in excess flow.
(3) Filler Valve. Some designs combine this function with the build-up and vent valve assembly as shown in figure AC 29 MG 6-2.
(4) Build-up and Vent Valve Assembly. This valve is positioned in the “vent” position when the system is being filled with oxygen and in the “build-up position at other times. Some designs combine this function with the filler valve as shown in figure AC 29 MG 6-2.
(5) Pressure Build-up Coil Assembly and Pressure Closing Valve.
With the build-up and vent valve in the “build-up” position gas that is formed is allowed to apply pressure to the liquid to provide adequate flow through the check valve to the evaporating coil assembly. A connection to a pressure relief valve is also provided.
(6) Evaporating Coil Assembly. This is provided to convert the liquid oxygen into a gaseous form. The evaporating coil assembly should be of sufficient capacity to maintain the design flow quantity to the dispensing regulators at a temperature within +10 and -20°F of cabin ambient temperature. MIL-D-19326G contains a discussion of installation considerations for this unit.
(7) Vent Line. Gaseous oxyg en escapes through this line. At the conclusion of the fill operation, liquid oxygen will flow overboard in a steady stream from System Components. All components should be aircraft qualified and Page MG 6 - 9
AC 29-2C, Chg 4 2/27/2014 this line to indicate the container is full of liquid oxygen. The vent line should be located to drain overboard at the bottom of the rotorcraft fuselage. Flow from the overboard vent should be directed so as not to create a hazard for personnel and not allow liquid oxygen to come in contact with the rotorcraft. The vent lines should be insulated to prevent frosting and sweating if they pass over equipment that will be harmed by water dripping from the lines, or drip pans should be installed under the lines. There should be no hydrocarbon fills or drains, forward or above, in proximity to the vent outlet.
(8) Regulator. A regulator should be installed in the supply line downstream from the heat exchanger. The regulator s hould reduce the liquid oxygen converter operating pressure to a supply pressure of 50 pounds per square inch gauge (PSIG) to be compatible with the normal operating pressure of medical oxygen equipment.
(9) Flow Control Valve. This valve provides a calibrated flow of gaseous oxygen from an operating supply of 50 ± 5 PSIG. A valve whose proof pressure is specified at 80 PSIG and has a burst pressure rating of 350 PSIG would be considered satisfactory.
(10) Check Valve. This va lve prevents gaseous oxygen in the supply system from backing up into the liquid oxygen in the container and increasing the vaporization rate of the liquid oxygen by exposure to the gas. This valve is normally an integral part of the liquid oxygen converter assembly.
(11) Quantity Indicators. A quantity indicator should be installed at the appropriate rotorcraft crew station to permit monitoring of the liquid oxygen supply. The indicator when installed in the rotorcraft should indicate the amount of liquid oxygen in the converter. Adequate clearance should be provided for the indicator connectors so that they can be readily disconnected by servicing personnel. Provisions should be made for the storage of the rotorcraft connectors to the liquid oxygen converter when they are disconnected. Liquid oxygen quantity i ndicating equipment is available in three types: capacitance gauging, electro-mechanical transducer indication, and differential pressure type indication.
(12) Pressure Relief Valves. Pr essure relief valves are provided to vent overboard through the overboard vent system any excess pressures developing within the system.
(13) Lines. Lines should be ei ther solid tubing or flexible hoses.
Examples of acceptable solid tubing are aluminum alloy conforming to AMS 4071 or corrosion resistant annealed steel (304) confirming to MIL-T-8506. Flexible hoses should be used for rotorcraft system connections to removable converters and to other applications where relative movement may occur. Flexible hoses should be wire-braidcovered bellows or wire-braid-covered tetrafluoroethylene. Flexible hoses conforming to MS90457 or MS24548 are satisfactory. MS90457 hose is flexible to -297°F (-183°C), and MS24548 hose is flexible to -65°F (-54°C). Sy nthetic lines such as plastic, nylon, or Page MG 6 - 10
rubber should not be used for lines subjected to continuous pressure, or for application where the line will not be visible. Lines that are not visible are those that are located behind liners or in the walls of the fuselage.
(14) Fittings. If in contac t, dissimilar metals should be suitably protected against electrolytic corrosion. Line assemblies should be terminated with “B” nuts or a similar manufactured terminating connection. Universa l adapters (AN 807) or friction nipples used in conjunction with hose clamps should be avoided in pressurized systems.
(15) Drain Valve. Systems t hat have permanently installed containers should include a drain valve located to allow for complete draining of the liquid oxygen container. An acceptable drain valve would be one in accordance with MK-V-25962 that is suitably capped. A cap in a ccordance with AN 929-5 with a permanently attached chain is a suitable cap.
(16) Low Pressure, Low Level Warning System. It is recommended that provisions be included in the system to alert the appropriate aircraft crew member that the level of the oxygen supply has reached some low level. It is recommended that low level be actuated when less than 10 percent of the full container capacity is available. If low system pressure is also monitored, the low pressure valve selected should be such that any drop in supply line pressure upon inhalation should not activate the low pressure warning function.
(C) Component Installation. The following are typical installation considerations that should be addressed when designing the oxygen system.
(1) Location. The oxygen equipment, lines, and fittings should be located as remotely as practicable from sources of flammable fluids, high heat and electrical items, fuel, oil, hydraulic fluid, batteries, exhaust stacks, manifolds, and so forth. Oxygen lines should not be grouped with lines carrying flammable fluids. If possible, converters should not be in line with the plane of rotation of a turbine. System components should not be installed in an environment that will exceed the temperature limit of the component, and no part of the system should be installed in an area that will exceed 350°F (176°C). To minimize loss due to heat, the liquid oxygen converter should not be located near equipment that dissipates a high quantity of heat.
(2) Converter Mounting. The oxygen container should be readily accessible to servicing personnel. If the container is not removable for servicing, the filler should be external to the aircraft with adequate contamination protection.
Mounting provisions for the converter and plumbing to the evaporating coil assembly should include a drain pan with an overboard drain.
(3) Flexible Hoses. Hoses s hould be of sufficient length to provide unstressed connections and be protected against chafing on surfaces or objects that may damage the wire covering. The bend radius imposed on the hoses during Page MG 6 - 11
AC 29-2C, Chg 4 2/27/2014 installation and replacement should not be less than the minimum established by the hose specifications.
(4) Lubricants. No lubricant s should be used on liquid oxygen pipe fittings. MIL-T-27730 Teflon tape may be used on male pipe fittings when required.
Teflon tape should not be used on flared tube fittings, straight threads, coupling sleeves, or on the outer side of tube flares. None of the tape should be allowed to enter the inside of a fitting. Krytox fluorinated gr ease by E.I. Dupont De Nemours and Company, or an equivalent, may be used sparingly on seals.
(5) Tubing Routing and Mounting. There should be at least 2 inches of clearance between the oxygen system and flexible moving parts of the rotorcraft. There should be at least a ½-inch clearance between the oxygen system and rigid parts of the rotorcraft. The oxygen system tubing, fittings, and equipment should be separated at least 6 inches from all electrical wiring, heat conduits, and heat emitting equipment in the rotorcraft. In sulation should be provided on adjacent hot ducts, conduits, or equipment to prevent heating of the oxygen system. In routing the tubing, the general policy should be to keep total length to a minimum. Allow for expansion, contraction, vibration, and component replacement. All tubing should be mounted to prevent vibration and chafing. This should be accomplished by the proper use of rubberized or cushion clips installed at 24-inch intervals (copper) or 36-inch intervals (aluminum) and as close to the bends as possible. The t ubing, where passing through or supported by the rotorcraft structure, should have adequate protection against chafing by the use of flexible grommets or clips. The tubing shou ld not strike against the rotorcraft structure during vibration and shock encountered during normal use of the rotorcraft.
(6) System Marking. The ro torcraft should be permanently and legibly marked, as applicable, in the locations specified below (a minimum letter height of ¼ - inch is recommended):
(i) Adjacent to the overboard vent opening:
CAUTION
LIQUID OXYGEN VENT
(ii) On outside surface of filler box cover plate:
LIQUID OXYGEN (BREATHING) FILL ACCESS
(iii) On underside surface of filler box cover plate:
CAUTION - KEEP CLEAN, DRY, AND FREE FROM OILS Page MG 6 - 12
(iv) In prominent place when filler box is open, preferably near liquid oxygen drain valve:
DO NOT OPEN DRAIN VALVE UNTIL DRAIN HOSE
AND DRAIN TANK ARE CONNECTED
(v) Other placards, such as one at the converter cautioning about the presence of liquid oxygen, may also be appropriate.
(7) Other installation criteria are given in Chapter 6 of AC 43.13-2, Acceptable Methods, Techniques, and Practices-Aircraft Alterations, and should be given consideration.
(D) Precautions. The referenced Society of Automotive Engineers (SAE) report contains precautions peculiar to a liquid oxygen installation, and this material should be reviewed. It should also be emphasized that liquid oxygen equipment and the aircraft being serviced must be electrically grounded during servicing to prevent an accumulation of static electricity and discharge. The fo llowing considerations are included for special emphasis:
(1) System Cleanliness. The completed installation should be free of oil, grease, fuels, water, dust, dirt, objectionable odors, or any other foreign matter, both internally and externally prior to introducing oxygen in the system.
(2) Closures. Lines that need to be disconnected during rotorcraft maintenance checks or overhaul, due to the location of the converter within the rotorcraft, should be capped to prevent materials that are incompatible with oxygen from entering the system when the system integrity is broken. C aps that introduce moisture and tapes that leave adhesive deposits should not be used for these purposes. All openings of lines and fittings should be kept securely capped until closed within the installation.
(3) Degreasing. All components of the oxygen system should be procured for oxygen service use in an “oxygen clean” condition. Parts of the oxygen system, such as tubing, not specifically covered by cleaning procedures should be degreased using a vapor phase trichloroethane degreaser. Ultrasonics may be used in conjunction with vapor phase degreasing for the cleaning of components.
(4) Purging. The system should be purged with hot, dry 99.5 percent pure oxygen gas in accordance with the manufacturers recommendations after:
(i) Initial assembly of the oxygen system; and
(ii) After system closure whenever the oxygen system pressures have been depleted to zero, or the system has been left open to atmospheric conditions for a period of time or is opened for repairs.
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AC 29-2C, Chg 4 2/27/2014
(5) Maintenance and Replacement. All parts of the oxygen system should be installed to permit ready removal and replacement without the use of special tools. All tubing connections and fittings should be readily accessible for leak testing with a leak test compound formulated for leak testing oxygen systems and for tightening of fittings without removing surrounding parts.
(ii) Gaseous Oxygen.
(A) General. This guidance is intended to supplement the existing guidance in AC 43.13-2, Chapter 6. If there are any differences within the two ACs, this guidance prevails since it pertains specifically to part 29 requirements.
(B) System Components.
(1) High Pressure Cylinders. Many installations utilize hospital type cylinders rather than aviation type cylinders. A concern with the hospital type cylinders is the yoke and the hard plastic washer that is commonly used with these cylinders. It is very difficult to properly attach these yokes since the rotorcraft provides a high vibration environment and no positive lock is provided. Leaks are a continuous problem with this configuration. Yokes are ava ilable for these bottles that provide for a positive lock.
Improved washers that provide for a good elastomeric seal and include a metal ring to limit crushing the washer are also available. If the hospital type bottles are to be used, only the modified yokes and improved seals should be considered for future installations. The preferred cylinder is the aviation type cy linder with the integral shutoff valve and regulator. All cy linders should be DOT approved.
( 2 ) L i n e s .
(i) General. Any lines that pass through potential fire zones should be stainless steel.
(ii) High Pressure. Use of high pressure lines may be necessitated by the use of a pressure regulator that is remote from the cylinder. The intent is to locate the regulator as close as physically possible to the cylinder, and to minimize the use of fittings. Lines of 6-inch lengths are encouraged with 18-inch lengths being the maximum in unusual circumstances. Lines made of stainless steel are recommended.
(iii) Low Pressure. Although lines may only be subjected to low pressures, if they are located behind upholstery or for any reason are not 100 percent visible during normal operation, they should be solid metal lines or high pressure flexible lines that conform to SAE 100R14A specifications for stainless braided hoses. Other oxygen lines, so called “green lines,” should only be used in locations that are 100 percent visible during normal operation. Th is would restrict their use to the run between the mask and the bulkhead disconnect in the aircraft cabin. Synthetic lines such as plastic, nylon, or rubber are not recommended for applications that will be Page MG 6 - 14
exposed to continuous pressure (i.e., as opposed to pressurized when needed). These materials can cold flow.
(3) F i t t i n g s.
(i) High Pressure. Inter cylinder connections are made with regular flared or flareless tube fittings with stainless steel. Usually fittings are of the same material as the lines. Mild steel or alumi num alloy fittings with stainless steel lines are discouraged. Titanium fittings should never be used because of a possible chemical reaction and resulting fire.
(ii) Low Pressure. Fittings fo r metallic low pressure lines are flared or flareless, similar to high pressure lines. Line assemblies should be terminated with “B” nuts in a similar manner to a manufactured terminating connection. Universal adapters (AN 807) or friction nipples used in conjunction with hose clamps are not accepted for use in pressurized oxygen systems.
(4) Shut-off Valve. Each system should contain a shutoff valve that is located as close as practical to the high pressure cylinder(s), and it should be assessable to a flightcrew member. High pressure cylinder s should use slow opening and closing system shut-off valves. Where the regulator is part of the cylinder, and low pressure oxygen is controlled, the emphasis in slow acting valves is not as significant, and use of a flow fuse may be possible. Us e of a flow fuse must be supported by a system fault analysis and testing to show maximum normal flow will not result in nuisance trips, and reliable trips will be provided for malfunction conditions resulting in excess flow.
(5) Regulators. The regulator should be mounted as close as possible to the cylinders (see paragraph b.(10)(i)(B)(8) of this guidance). If non-aviation qualified regulators are considered, their service history should be reviewed and careful consideration given to the manufacturer’s environmental qualification. Radio Technical Commission for Aeronautics Document D0-160 is a recognized and accepted standard for environmental considerations. As a mi nimum, consideration should be given to operation during altitude, temperature, and vibration extremes.
(6) Placards. Appropriate placards should be provided with the installed system. Emphasis should be placed on any precautions that are appropriate during filling of the system and so forth.
(7) Filler Connections. When a filler connection is provided, it is recommended it be located outside the fuselage skin or isolated in a manner that would prevent leaking oxygen from entering the rotorcraft. Careful evaluation should also be made of any nearby sources of fuel, oil, or hydraulic fluid under normal or malfunction conditions. Each filler connection should be placarded. In addition, any valves (on aircraft or ground servicing equipment) associated with high pressure should be slow acting.
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