AC 27-1BChg 4 12/15/2009 Page MG 5 - 8
CHAPTER 3
AIRWORTHINESS STANDARDS
NORMAL CATEGORY ROTORCRAFT
MISCELLANEOUS GUIDANCE (MG) AC 27 MG 6. EMERGENCY MEDICAL SERVICE (EMS) SYSTEMS INSTALLATIONS INCLUDING: INTERIOR ARRANGEMENTS,
EQUIPMENT, HELICOPTER TERRAIN AWARENESS AND
WARNING SYSTEM (HTAWS), RADIO ALTIMETER, AND FLIGHT DATA MONITORING SYSTEM.
a. Explanation. This section pertains to EMS configurations and associated rotorcraft airworthiness standards. EMS configurations are usually unique interior arrangements that are subject to the appropriate airworthiness standards, part 27 or its predecessor CAR part 6, to which the rotorcraft was certificated. No relief from the standards is intended except by § 21.21(b)(1) or an exemption. EMS configurations are seldom, if ever, done by the original manufacturer.
(1) The FAA has specified in the operating rules the minimum equipment required to operate as a helicopter air ambulance service provider (identified by an "*" in this guidance). This equipment, as well as all other equipment presented for evaluation and approval, is subject to compliance with airworthiness standards. Any equipment not essential to the safe operation of the aircraft may be approved provided the use, operation, and possible failure modes of the equipment are not hazardous to the aircraft. Safe flight, safe landing, and prompt evacuation of the rotorcraft in the event of a minor crash landing, for any reason, are the objectives of the FAA evaluation of interiors and equipment unique to EMS.
(1) For example, a rotorcraft equipped only for transportation of a non-ambulatory person (e.g., a police rotorcraft with one litter) as well as a rotorcraft equipped with multiple litters and complete life support systems and two or more attendants or medical personnel may be submitted for approval. These configurations will be evaluated to the airworthiness standards appropriate to the rotorcraft certification basis.
(il) Normal category rotorcraft should comply with flightcrew and passenger safety standards, which will result in the need to reevaluate certain features of the basic certified rotorcraft related to the EMS arrangement, such as doors and emergency exits, and occupant protection. Compliance with airworthiness standards results in placards or markings for doors and exits, exit size, exit quantity and location, exit access, safety belts, and possibly shoulder harnesses or other restraint or passenger protection means to be retained as part of the rotorcraft's basic type design. These features, including any placards and markings required as part of the rotorcraft's basic type design, should be retained unless specific replacements or alternate designs are necessary for the EMS configuration to comply with airworthiness standards.
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(2) Many EMS configurations of normal rotorcraft are equipped with the following:
(i) Attendant and medical personnel seats, which may swivel.
(ii) Multiple litters, some of which tilt.
(iii) Medical equipment stowage compartments.
(iv) Life support and other complex medical equipment.
(v) Human infant incubator (isolette).
(vi) Curtains or other interior light shielding for the flightcrew station.
(vii) External loud speakers and search lights.
(viii) Special internal (intercom) and external communication radio equipment.
*(ix) Flight data monitoring system (FDMS).
*(x) Radio altimeter.
*(xi) Helicopter terrain awareness and warning system (HTAWS).
*(3) All helicopter air ambulance service providers are required to operate at all times under a part 135 subpart L certificate. The equipment required to obtain operational approval includes:
*(i) FDMS. The installation guidance is in paragraph b. (13) of this MG.
*(Il) Radio Altimeter (RAD ALT). The installation guidance is in paragraph b. (14) of this MG.
*(iii) HTAWS. HTAWS is required for operation under part 135 subpart L, Helicopter Air Ambulance Equipment, Operation, and Training Requirements;
§ 135.605, Helicopter Terrain Awareness and Warning System (HTAWS). The design standards are in Technical Standard Order (TSO)-C194 and the installation guidance is in AC 27-1 MG 18.
b. Procedures.
(1) General.
(i) Original type design information and criteria may or may not be available from the manufacturer. Availability of this information is dependent on whether the information is considered "public" (i.e., non-proprietary) or proprietary. It may be Page MG 6 - 2
appropriate to reference the helicopter manufacturer's "standard" features, placards, and markings in the applicant's modification design data.
(ii) The EMS modification presented for approval usually contains equipment of one manufacturer's model or design. The type design of the modification will have features to power and restrain the equipment, maintain the rotorcraft systems integrity, and to otherwise protect the occupants. See paragraph b. (17), which refers to equipment substitution.
(iii) All equipment installations in the helicopter must be approved. EMS helicopters typically include operations in which large medical equipment is not installed in the helicopter but instead is carried onto the helicopter, as needed, such as isolettes, large medical equipment, and other medical items. This equipment is not included as part of the rotorcraft type design modification because it is not considered a permanent installation in the helicopter. However, carry-on medical equipment must be evaluated as to how it affects the safety of the helicopter and its occupants (including the occupant in the isolette) while being carried in the helicopter. This carry-on equipment (including the isolette must be properly restrained so it is not a hazard during flight operations.
Consequently, the means to stow or store the medical carry-on items must be evaluated for the appropriate load factors relative to the helicopter such that the means for stowage of the carry-on equipment does not fail. For instance, in the case of a carry-on Isolette, the isolette is typically placed on top of an installed "mount" for the isolette. The "mount" is evaluated for carriage and restraining of the isolette. In some cases, an isolette may be completely self-contained and include other items, such as oxygen bottles required for the isolette occupant, which must also be evaluated for carriage of that equipment.
(2) Evacuation and Interior Arrangements. Access to the emergency exits or doors from any location in the cabin or compartment, access to and use of the exit or door opening means or release device, and the unobstructed area of an exit are potential problems that should be addressed in the early design stage. Multi-litter arrangements may be especially critical for normal category rotorcraft due to their limited space.
(i) The operation or use of devices for locking the position of swivel seats and for rapid installation and removal of litters (isolettes, etc.) should be labeled unless they are simple and obvious, and do not require exceptional effort. The design features of the device(s) and the seat or litter will influence the extent of information in any label necessary to ensure proper and safe installation for routine use and prompt evacuation when appropriate or necessary for the interior arrangement. The requirement for labels or markings (instructions, etc.) that applies to operation of seat or litter features, release devices, etc., is not relieved even if attendants are necessary for an evacuation as discussed in paragraph b.(2)(iii). Placards or instruction cards that contain evacuation procedures do not necessarily contain detailed procedures for individual seats, litters, and so forth. Release devices that are simple and obvious and do not require exceptional effort are recommended. For example, a single central control for litter Page MG 6 - 3
AC 27-1B, Chg 4 2/27/2014 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 should not be partitioned to impede access to exits. Exits and doors should be readily accessible. A door or exit is required on each side of the rotorcraft. A demonstration or a "walk-through" of appropriate evacuation procedures may be necessary to ensure the means and procedures are feasible and adequate. Rotorcraft with readily accessible exits, using simple and obvious means and procedures for an evacuation, may not require written procedures or a demonstration.
Placards and durable markings, if necessary, may be sufficient to complement the exit markings and instructions required by the standards.
(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 patient 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 ambulatory 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 purpose 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.
Restraint of Occupants and Equipment. The emergency landing conditions specified in § 27.561(b) dictate the design load conditions. See AC 27-1, sections 27.561 and
27.785 for further information.
(i) Whether seated or recumbent, the occupants must be protected from serious head injury as prescribed in § 27.785. Swivel seats and tilt litters may be used provided they are substantiated for the appropriate loads for the positions selected for approval.
Placards or markings may be used to ensure proper orientation for flight, takeoff and 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 § 27.561(b).and § 27.785(k). Harnesses 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 Page MG 6 - 4
materials are also subject to the flammability standards noted in paragraph b.(4). The litters) and isolettes) 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 EMS type design, it may be considered a carry-on item and not part of the EMS type design. In these cases, there is typically a means to position the carry-on 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, the load factors specified in that AC may not be appropriate for some 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 27.561(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 should also contain the contents for 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 use 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.
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(4) Flammability of Materials.
(i) Interior materials must meet the flammability standards in § 27.853, appropriate to the type design. The standard presently requires compartment materials to be at least flame resistant. The wall and ceiling linings, coverings of upholstery, floors, and furnishings must be at least flame resistant.
(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.
(C) Self-extinguishing materials that can meet the transport rotorcraft standards of § 29.853 of Amendment 29-17 are recommended for use in normal category rotorcraft.
When the isolette is included in the EMS configuration approval, the isolette materials are subject to the flammability standards of § 27.853. The current standards require that all materials, including transparencies, fabric (e.g., padding, covers), straps, etc., be flame-resistant for each compartment used by the crew or passengers. AC 23-2 also contains test information about flash and flame-resistant material.
(5) Exit Signs or Markings and External Markings. Doors and exits must have signs and markings (instructions) for prompt evacuation even in darkness. An emergency light system is not required by part 27. Refer to the RFM or maintenance manual for standard placards, decals, stencils, etc. Alternates may be approved as a part of the interior type design.
(6) Interior or "Medical" Lights. The view of the flightcrew 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 that meet the flammability standards (flame resistant) may be used. Complete partitioning or separation of the flightcrew and passenger area is not prudent. Means for visual and oral communication are usually necessary. Refer to AC 27-1 section 27.773, 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.
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(8) External Devices.
• The lights 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.
That is, the landing gear should deflect under limit load without causing damage to the device. For example, if the gear limit landing load deflection is 8 inches, the device would need to have at least an 8-inch ground clearance to avoid contact with the landing surface.
(iii) The physical characteristics of the rotorcraft landing gear design dictate the necessary clearance. The type design owner has this design information. A conservative deflection value may be chosen in place of obtaining design information.
(The limit landing descent velocity specified in § 27.725(a) ranges from 6.5 to 8.3 feet per second.)
(iv) The device should also be designed and located to preclude penetration into a critical area of the fuselage such as fuel cell, fuel line, primary control tube, or occupant seat in the event of higher landing impact velocities.
(v) 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 alternative 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.
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(9) Miscellaneous. Several paragraphs in this MG contain guidance for the standards cited in the Regulatory Sections 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 rotorcraft 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 27 MG 6-1 and AC 27 MG 6-2. The installation may provide 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.
(B) System Components. All components should be aircraft qualified and 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 should 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. Aircraft 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 installations, 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 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.
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(3) Filler Valve. Some designs combine this function with the build-up and vent valve assembly as shown in figure AC 27 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 27 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.
1) Vent Line. Gaseous oxygen escapes through this line. At the conclusion of the fill operation, liquid oxygen will flow overboard in a steady stream from 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 should 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 valve 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 Page MG 6 - 9
AC 27-1B, Chg 4 2/27/2014 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 indicating equipment is available in three types: capacitance gauging, electro-mechanical transducer indication, and differential pressure type indication.
(12) Pressure Relief Valves. Pressure relief valves are provided to vent overboard through the overboard vent system any excess pressures developing within the system.
(13) Lines. Lines should be either 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). Synthetic lines such as plastic, nylon, or 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 contact, dissimilar metals should be suitably protected against electrolytic corrosion. Line assemblies should be terminated with "B" nuts or a similar manufactured terminating connection. Universal adapters (AN 807) or friction nipples used in conjunction with hose clamps should be avoided in pressurized systems.
(15) Drain Valve. Systems that 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 accordance 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.
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(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 should 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 installation and replacement should not be less than the minimum established by the hose specifications.
(4) Lubricants. No lubricants 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 grease 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. Insulation 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 tubing, 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 should not strike against the rotorcraft structure during vibration and shock encountered during normal use of the rotorcraft.
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