7/30/97 АС 27-1A on a smooth, level asphalt surface. For rotorcraft equipped with wheels and/or landing gear struts, the maximum system deflections should be considered when determining the 5 inches of acceptable static ground clearance. The 5-inch ground clearance would only apply to original configuration of newly manufactured rotorcraft. However, a 3-inch ground clearance has been found acceptable and may be approved for skid gear equipped rotorcraft to account for the in-service permanent set allowed for skid gear members, (i.e., cross tube deflections allowed per the maintenance manual). Cable supported systems, (i.e., cargo hook installations) or dispensing systems utilizing flexible ducts (certain types of dry material dispensing equipment which may or may not be retractable) have been approved even though portions of the system may contact the surface during a normal landing.
(7) A number of rotorcraft are approved for external cargo operations that allow a gross weight higher than the approved internal gross weight limit. This difference is usually due to the allowable weight limit restriction of the landing gear. (The gear is not approved for the higher weight.) Those types of dispensing equipment, that can be loaded in flight to a weight that exceeds the allowable limit of the landing gear should incorporate a reliable means that rapidly reduces the total aircraft gross weight to within allowable landing gear limits. In most cases, this will involve jettison of the disposable load. The time interval for this operation should be demonstrated, and should not exceed a recommended 3 seconds from a level flight condition.
(8) A flight check or demonstration of the agricultural dispensing equipment installation is normally conducted. This flight check should also qualitatively determine that no hazardous deflection or resonance in the rotorcraft or dispensing system exists.
This flight check should be conducted in accordance with the requirements of FAR 133.41.
(9) For rotorcraft certificated in dual categories, the inspection requirements of FAR 21.187(b) must be observed when converting from restricted to normal category.
c. Acceptable Means of Compliance.
(1) Analysis Method. Structural analysis (static) may be used if the structure is of a configuration for which experience has shown the method to be reliable. 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, mounting hardware, and support structure should all be substantiated to the load conditions specified by this paragraph considering the effects of internal fluid pressures when applicable.
(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 Par 785 1089
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 and/or analysis. Static test loads should be applied in combination with associated internal fluid pressure loadings. The ultimate loads specified in Paragraph 785 should be sustained for at least 3 seconds without failure.
(3) Dynamic Tests.
(i) If the applicant elects to test to the load factors noted herein, 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.
(il) The tank and mounting hardware should support ultimate loads without detrimental permanent set or failure, respectively. The rotorcraft support structure may be included in the dynamic tests, or it may be substantiated separately via static test and/or analysis for each condition specified by this paragraph.
(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.
1090 Par 785
or 11 ½ TANK FIGURE 785-2. SKETCH OF TANK PRESSURE TEST Par 785 1091
АС 27-1А 7/30/97
786. EMERGENCY MEDICAL SERVICE (EMS) SYSTEMS, INSTALLATIONS, INTERIOR ARRANGEMENTS, AND EQUIPMENT.
a. Explanation. This paragraph pertains to EMS configurations and associated rotorcraft airworthiness standards. EMS configurations are usually unique interior arrangements that are subject to the appropriate airworthiness standards, FAR 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 exemption. EMS configurations are seldom, if ever, done by the original manufacturer.
(1) The FAA/AUTHORITY has not specified in the airworthiness or operating rules the minimum equipment for an EMS configuration. Whatever equipment is presented for evaluation and approval is subject to compliance with the airworthiness standards. Any equipment that is not essential to safe operation of the aircraft is evaluated for a "no hazard approval," i.e., it is optional equipment and 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/AUTHORITY evaluation of interiors and equipment unique to EMS.
For example, a rotorcraft equipped only for transportation of a nonambulatory person (a police rotorcraft with one litter) as well as a rotorcraft equipped with multiple litters and complete life support systems and two or more trained attendants/medical personnel may be submitted for approval. These configurations will be evaluated to the airworthiness standards appropriate to the rotorcraft certification basis.
(її) Normal category rotorcraft should comply with flightcrew and passenger satety standards which result in certain features of the basic certified rotorcraft which are related to the arrangement, to the doors and emergency exits, and to occupant protection. Compliance with the 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 as a part of a rotorcraft type design. These features, including any placards and markings which are required to be a part of the rotorcraft type design, should be retained unless specific replacements or alternate designs are necessary for the EMS configuration to comply with the airworthiness standards.
(2) Many EMS configurations of normal rotorcraft are equipped with the tollowing:
Attendant/medical personnel seats, which may swivel.
(i) Multiple litters, some of which tilt.
1092 Par 786
(III) Medical equipment stowage compartments.
(iv) Life support and other complex medical equipment.
(v) Incubators for infants.
(vi) Curtains or other interior light shielding for the flightcrew station.
(vii) External loud speakers and search lights.
(vili) Special internal (intercom) and external communication radio equipment.
b. Procedures.
(1) General Original type design information and criteria may or may not be available from the manufacturer. This may be "public," not proprietary, information that is pertinent for interior modifications. It may be appropriate to include "standard" features, placards, and markings for the rotorcraft type design by reference 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(15) which refers to equipment substitution.
(2) Evacuation and Interior Arrangements. Access to the emergency exits/doors from any location in the cabin/compartment, access to and use of the exit/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. Multilitter arrangements may be especially critical for normal category rotorcraft.
The operation or use of devices for locking the position of swivel seats, etc., and for rapid installation and removal of litters (incubators, 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 and/or litter will influence the extent of information in any label necessary to insure proper and safe installation for routine use and for 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 trained attendants are necessary for an evacuation as discussed in c(2)(v). Placards or instruction cards that Par 786 1093
contain evacuation procedures do not necessarily contain detail 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 release would be preferred over multiple action release devices. Seats and litters which require multiple actions or steps to position or release for an emergency evacuation after minor crash landing may be acceptable if properly scrutinized and evaluated for the effect on achieving a rapid evacuation.
The passenger compartment should not be partitioned to impede access to exits. Exit/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 insure 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.
(i) It is preferable for the patient to remain strapped in the litter; however, the patient may be removed from the litter to facilitate prompt evacuation in the event of a minor crash landing as defined in § 27.561(b). If evacuation procedures and trained attendants are necessary for rapid evacuation, the procedures may be prominently displayed in durable markings, placards, cards, and summarized or condensed in the Emergency Procedures Section of the Rotorcraft Flight Manual (RFM) or an EMS configuration supplement to the RFM. If medical attendants are required for evacuation, the attendants should be trained in evacuation procedures and listed as trained attendants in the Limitations Section of the RFM or supplement. A trained attendant is not considered a flightcrew member but is a required "crewmember."
(3) Restraint of Occupants and Equipment.
The minor crash conditions specified in § 27.561(c) usually dictate all but the vertical (down and possibly up) design load conditions. The flight and landing loads, such as 13.5g limit (flight) vertical, usually override the minor crash loads. See Paragraphs 218 and 336 of this AC for further information.
Galleys, medical supplies, and equipment compartments or modules should be restrained and the individual compartments should also contain the contents therein for the conditions noted in b(3)(i)., 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/engagement should be used to contain the contents for the conditions noted. If necessary, a static load test or analysis should be employed to insure the container/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 use of a magnification factor 1094 Par 786
with the design conditions noted. Prudent design and location of compartments having heavy, unrestrained (loose) equipment will mitigate the potential effects of minor crash impact loads.
(iii) Whether seated or recumbent, the occupants must be protected 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 assure proper orientation for flight takeoff and landing and minor crash conditions. For recumbent occupants, harnesses, straps, a padded headboard, a diaphragm, or safety belts may be used if proven for the forward and lateral loads of §27.561(c). Harnesses/straps are preferred, however, for the forward condition. When harnesses/straps are used, they should prevent the occupant from significant forward motion (4g condition) that would remove the support for the head as well as the shoulder for "head-down" motion. The litter design should become a part of the interior design approval. The type design for the interior should include the litter and incubator part numbers. Infants in incubators should be similarly protected by padding and containment within the incubator with the incubator restrained for the load cases noted. If the infant is strapped to a removable platform, the platform and infant should be properly restrained within the incubator for the load cases noted. Incubator materials are also subject to the flammability standards noted in Paragraph b(4) that follows.
(4) Flammability Standards for Materials.
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 flash 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 for further information.
(B) Flame-resistant material may be characterized as that not exceeding a 4-inch-per-minute (horizontal) burn rate.
(C) However, self-extinguishing materials that can meet the transport rotorcraft standards of § 29.853 of Amendment 29-17 are readily available.
These self-extinguishing materials are recommended for use in normal category rotorcraft.
(i) For incubators, transparencies must be flash resistant and fabric (padding, covers) straps, etc., must be flame resistant according to the standard.
Advisory Circular No. 23-2, Flammability Tests, dated August 20, 1984, contains test information about flash and flame-resistant material.
Par 786 1095
АС 27-1A 7/30/97
(5) Exit Signs/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 "standards" 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. 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. Reference Paragraph 331 of this AC concerning pilot visibility (§ 27.773).
(7) External Devices.
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 proven for the flight and landing conditions and possibly for the minor crash conditions where applicable. Pilot view/visibility should not be adversely affected by the lights and reflections from the lights.
(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 must 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 proprietary design information. A conservative deflection value may be chosen in place of obtaining proprietary 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) In addition, flight evaluation is necessary to determine the effects of the device on the rotorcraft flight characteristics and on flightcrew night visibility.
(8) 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 must be installed or the patient must be restrained to prevent inadvertent or potential 1096 Par 786
convulsive interference with safe operation of the rotorcraft. The guard may be a part of the rotorcraft interior features. In addition, prompt evacuation must be assured if a guard is used.
(9) Miscellaneous. Several paragraphs in this AC contain guidance for the standards cited in the reference list (reference 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) Liquia Oxygen (A) System General Description. This section covers specific requirements for liquid oxygen systems. 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 786-1 and 786-2. 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.
(≤) Shutoff Valve Assembly. This valve should 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 Par 786 1097
pressure is low, the use of an electrically actuated shutoff valve is satisfactory to accomplish this tunction. 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.
Filler Valve. Some designs combine this function with the build-up and vent valve assembly as shown in figure 786-2.
(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 786-2.
(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 impinge on the rotorcraft. The vent lines should be insulated to prevent frosting and sweating if they pass over equipment which 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.
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.
Flow Control Valve. This valve provides a calibrated flow of gaseous oxygen from an operating supply of 50 + 5 PSIG. A valve whose proof 1098 Par 786
7/30/97 АС 27-1A 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 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-braid-covered bellows or wire-braid-covered tetrafluoroethylene. Flexible hose conforming to MS90457 or MS24548 would be considered 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 for use 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.
Par 786 1099
АС 27-1A 7/30/97
(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 should be of sufficient length to provide unstressed connections and be protected against chafing on surfaces or objects which may damage the wire covering. The bend radius imposed on the hoses by the installation and during remove and replace actions 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 1100 Par 786