(10) Recent service history has shown that external equipment and external fixture modifications that generate high drag loads in forward flight 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 identical 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.
(i) 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 premodification 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.
(ii) 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.
(11) For rotorcraft certificated in dual categories, the inspection requirements of § 21.187(b) must be observed when converting from restricted to normal category.
c. Acceptable Means of Compliance.
(1) Analysis Method. Static structural analysis may be used provided a methodology is applied that has been shown to be reliable for analyzing the type of structure. Structural substantiation of tanks that are designed to contain liquid materials may be accomplished by pressure testing. For tanks or hoppers designed to contain dry material (e.g., dust or fertilizer), static load tests may be used to verify structural integrity. The tank/hopper, mounti ng hardware, and support structure should all be substantiated to the load conditions specified and should consider the effects of internal fluid pressures, when applicable, in Figure AC 27 MG 5-1.
(2) Static Tests. Static tests of tank/hoppers, mounting hardware, and support structure for each critical load condition may be accomplished using conventional techniques; such as, dead weight loading, whiffletree systems, and hydraulic rams. If tests of the tank and its mounting hardware are conducted using a test fixture representing the rotorcraft, the rotorcraft support structure may be substantiated independently by means of test or analysis, or both. Static test loads should be applied in combination with associated internal fluid pressure loadings. The ultimate loads specified in Figure AC 27 MG 5-1 should be sustained for at least 3 seconds without failure.
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AC 27-1BChg 4 12/15/2009
(3) Dynamic Tests.
(i) If the applicant elects to test to the loading conditions in Figure AC 27 MG 5- 1, the maneuvering and gust loadings will be considered to be adequately substantiated. For each condition, the critical volume and density of fluid should be used.
(ii) The tank and mounting hardware should support ultimate loads without permanent elastic deformation failure, respectively. The rotorcraft support structure may be included in the dynamic tests, or it may be substantiated separately via static test or analysis, or both, for each condition specified in Figure AC 27 MG 5-1.
(4) Pressure Testing. Internal pressure loads may be applied using the water standpipe technique. Standpipe water height should be accurately computed for each critical spray tank static test loading. Pressure testing of spray tanks is not absolutely essential but is recommended for safety reasons. This testing will also determine whether the joints and connections are tight and will not leak in addition to determining any weak spots in the construction. Where spraying is done with highly volatile and flammable liquids, or where the tank has a return line, such as in an engine oil tank where the fluid is pumped back into the tank, it is recommended that the tank be tested for a pressure of 5 pounds per square inch. For other liquids, and where no fluid return line is used, testing to 3 ½ pounds per square inch should be satisfactory. There are many ways of pressure testing a tank, however, it is believed that the simplest and easiest method is to fill the tank with water and use a standpipe filled with water. A 1 1/8-inch pipe can be connected to the venting tube or one adapted to the filler opening. In either case, the height of the pipe would be the same. For a 3 ½ PSI test of the tank, the height of the water in the pipe would only need to be 8 feet and for a 5 PSI test only an 11 ½ -foot height of water will be needed. (See Figure AC 27 MG 5-2 below.)
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FIGURE AC 27 MG 5-2 SKETCH OF TANK PRESSURE TEST
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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.
(i) 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.
(ii) 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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AC 27-1B, Chg 4 2/27/2014
(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.
*(ii) 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 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 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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AC 27-1B, Chg 4 2/27/2014
(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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AC 27-1B, Chg 4 2/27/2014
(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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