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.
(6) System Marking. The rotorcraft 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 (Ш) On outside surface of filler box cover plate:
LIQUID OXYGEN (BREATHING) FILL ACCESS On underside surface of filler box cover plate:
CAUTION - KEEP CLEAN, DRY, AND FREE FROM OILS (LV) 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.
(Z) Other installation criteria are given in Chapter 6, AC 43.13-2A, Acceptable Methods, Techniques, and Practices-Aircraft Alterations, dated June 9, 1977, and should be given full consideration.
(D) Precautions. The referenced SAE report contains precautions peculiar to a liquid oxygen installation, and this material should be reviewed. It should Par 786 1101
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 following considerations are included for special emphasis:
(1) System Cleanliness. The completed installation shall 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 which are required to be disconnected, due to the location of the converter within the rotorcraft during rotorcraft maintenance checks or overhaul, should be capped to prevent materials which are incompatible with oxygen from entering the system when the system integrity is broken. Caps which introduce moisture and tapes that leave adhesive deposits shall not be used for these purposes.
All openings of lines and fittings shall 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:
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.
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 removal of surrounding parts.
(ii) Gaseous Oxygen.
(A) General. This guidance is intended to supplement the existing guidance in AC 43.13-2A, Chapter 6. If there are any differences within the two AC's, this guidance should prevail since it pertains specifically to Part 27 requirements.
(B) System Components.
1102 Par 786
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 available for these bottles that provide for a positive lock. Improved washers that provide for a good elastometric 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 cylinder with the integral shut-off valve and regulator. All cylinders should be DOT approved.
(2) Lines.
General. Any lines that pass through potential fire zones should be stainless steel.
(i) 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.
(ii) 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 such as Aeroquip 300 series hose or Stratotlex 124 or 170 series hose assemblies. The so called "green lines" should only be used in locations that are 100 percent visible during normal operation. This 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 cannot be recommended for applications that will be exposed to continuous pressure (i.e., as opposed to pressurized when needed). These materials can cold flow.
(3) Fittings.
High Pressure. Intercylinder connections are made with regular flared or flareless tube fittings with stainless stee. Usually fittings are of the same material as the lines. Mild steel or aluminum alloy fittings with stainless steel lines are discouraged. Titanium fittings should never be used because of a possible chemical reaction and resulting fire. An example of a series of fittings that has been accepted is the "SS" series Swagelok tube fittings (flareless).
Par 786 1103
Low Pressure. Fittings for 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 cylinders should use slow opening/closing system shut-off valves. Where the regulator is part of the cylinder, and low pressure oxygen is controlled, the emphasis on slow acting valves is not as significant, and use of a flow fuse may be possible. Use of a flow fuse must be supported by a system fault analysis and testing to show maximum flow will not result in nuisance trips, and reliable trips will be provided for malfunction conditions resulting in excess flow.
(2) Regulators. The regulator should be mounted as close as possible to the cylinders (reference b(9)(ii)(B)(2)(i)). If nonaviation qualified regulators are to be considered, their service history should be reviewed and careful consideration should be 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 minimum, consideration should be given to operation during altitude, temperature, and vibration extremes.
(Q) Placards. Appropriate, durable 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.
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 valve (on aircraft or ground servicing equipment) associated with high pressure should be slow acting.
(C) "Provisions Only" Considerations. In some instances systems are approved that only include provisions for a supply system consisting of the high pressure cylinders, regulators, and their associated lines and fittings. In these instances, a placard should be provided that refers to a supply system that is considered satisfactory for the remainder of the installation. Other supply system configurations may very well be acceptable; however, they should be evaluated by the ACO that evaluated the original installation. An example of an acceptable placard for this situation is:
1104 Par 786
Oxygen Supply System must be in accordance with the requirements given in STC SH _ Deviations to the configuration specified must be evaluated and approved by the Manager (include reference to the appropriate FAA ACO).
(11) Medical Communication Equipment. This equipment is provided to allow for communication between the rotorcraft and ground medical personnel. It includes voice communication and may also include telemetry equipment for the transmission of graphic data. It should be demonstrated that this equipment functions, and the range at which this determination was made should be recorded in the project file. The functional demonstration should include a 360° turn (clockwise and counterclockwise) to assure no significant sections of signal blanking exists. The remainder of the emphasis on this equipment should be to assure that operation of this equipment does not interfere with normal operation of any avionic systems whose installation is required for safe operation of the rotorcraft.
(12) Cabin Lighting. EMS interiors normally include higher intensity cabin lighting than other interiors. This lighting capability should be carefully evaluated to ensure it does not interfere with operation of the rotorcraft. In some installations a special curtain is required to separate the cockpit from any interference by the lighting.
The FAA/AUTHORITY project file should include a short discussion of how this evaluation was conducted. See Paragraph b(6) for other curtain considerations.
Other EMS Equipment. These items of equipment that are installed for the EMS mission are considered to be optional equipment and should be operated to assure they function properly. This evaluation would normally be done by someone that is knowledgeable about the particular type of equipment since correct operation of the equipment is essential to a valid determination that the required rotorcraft systems are not being interfered with. This includes all removable pieces of medical equipment that are used for patient care. The primary purpose of the evaluation of this equipment is to emphasize the possibility of any adverse interference between operation of the EMS equipment and the systems whose installation is required for safe operation of the aircraft, the adequacy of the installation provisions, and assurance that failure modes will not result in a hazardous condition for the rotorcraft.
(14) Miscellaneous. The following areas are not peculiar to EMS installations; however, their significance is enhanced by the complexity of an EMS installation.
Compatibility. Many EMS installations are a collection of several STC's and may also include some "FAA/AUTHORITY field approvals." For this situation it should be shown that the overall installation provides for safe operation of the aircraft. Operation of a search light, if included, should be emphasized since this system can be difficult to keep out of the cockpit.
Par 786 1105
АС 27-1A 7/30/97 (її) Electrical Load Analysis. An electrical load analysis should be conducted, and additional guidance is available in Paragraph 776 of this AC. If the analysis indicates the generators) can be overloaded, appropriate measures should be taken to account for the problem. In some instances a placard that specifies certain operating limitations may be satisfactory while in other instances an electrical interlock may be in order. In general, if the amount of overload is relatively small, the placard solution will probably be satisfactory; whereas, if the amount of possible overload is significant, it is more likely that an interlock scheme will be necessary.
(Ш) Aircraft Grounding. It should be emphasized in an appropriate place in the STC data (RFM, maintenance information, etc.) that any time the EMS systems are being operated or serviced (oxygen for example) on the ground, the rotorcraft itself must be grounded.
(iv) Electrical Outlets. All electrical outlets provided in the cabin should be the three-prong grounded type. When not in use, these outlets should be suitably protected against the entry of fluids.
(V) Placards. All medical outlets should be placarded (air, oxygen, vacuum, etc.). Electrical power outlets should be placarded for type of voltage and amperage capacity. A placard stating no smoking when oxygen is in use should be included. Other placards would include information appropriate to the oxygen system, operation of special controls, and so forth.
(vi) Equipment in Cargo and Baggage Compartments. When components are added to the baggage compartments, provisions should be made to protect the system components due to shifting cargo. In addition, when oxygen components are installed, the compartment should be placarded against the storage of oil or hydrocarbons. A smoke detector is recommended for a compartment if oxygen cylinders are installed in a closed, nonaccessible compartment. Also, the cargo weight limitations placard should be changed. Paragraph 337 of this AC pertains to cargo and baggage compartments.
(15) Equipment Substitution. The EMS modification that is presented for approval will contain specific items of equipment, and the approval will make reference to this equipment. If other equipment (new model, manufacturer, etc.) is to be substituted, then an evaluation should be made to assure the substitute equipment is also satisfactory. This evaluation would normally consist of comparing the attachment means, design features, failure modes, specifications, and operation of the two units.
The purpose of the evaluation is to assure there are not differences that have an adverse effect on the airworthiness of the installation. Other differences would not be considered significant. Specific seats and litters are generally approved as a part of the EMS configuration. Substitution may be approved in accordance with the standards.
c. Related FAR Sections and References.
1106 Par 786
7/30/97 АС 27-1A
(1) EAR Sections. § 27.337, 27.471, 27.561, 27.773, 27.783, 27.785, 27.807,
27.831, 27.853, 27.1301, 27.1309, 27.1353, 27.1357, 27.1365, 27.1367, 27.1411,
27.1413, 27.1431, 27.1557 (d), 27.1561, 27.1581(a)(2), 27.1583(d), 27.1585, and
27.1589.
(2) Other References.
(1) Helicopter Association International, Emergency Medical Services Recommended Guidelines, 1987, First Revision, 2 pages.
(ii) National Highway Traffic Safety Administration, Air Ambulance Guidelines, dated 1981.
(ili) FAR Part 91, General Operating and Flight Rules.
(iv) FAR Part 135, Air Taxi Operators and Commercial Operators.
(v) AC 67-1, Medical Information for Air Ambulance Operators, dated March 4, 1974.
(vi) AC 23-2, Flammability Tests, dated August 20, 1984.
(vii) Oxygen Equipment for Aircraft, Society of Automotive Engineers Aerospace Information Report No. 825B, Rev. 9/86.
(vili) Acceptable Methods, Techniques, and Practices--Aircraft Alterations, AC 43.13-2A, dated June 9, 1977.
(ix) Design and Installation of Liquid Oxygen Systems in Aircraft, General Specification for Military Specification MIL-D-19326G, dated October 1, 1985.
Par 786 1107
INTEGRAL ASSEMBLY AC 27-1A (Most Cases)
OVERBOARD
VENT LINE PRESSURE I BUILDUPIVENT
RELIEF VALVE TO
GAUGING SYSTEM
PRESSURE RELIEF CLOSING PRES. LIQUID
VALVE CONTAINER PATIENT TO — CONTROL FLOW VALVE REGULATOR EVAPO- PRES.
RATING BUILDUP FILL COIL COIL ¡VALVE
ASSEMBLY
EMERGENCY
SHUTOFF VALVE FIGURE 786-1 TYPICAL LIQUID OXYGEN SYSTEM 7/30/97 Par 786
INTEGRAL ASSEMBLY 7/30/97/ Par 786 (Most Cases)
OVERBOARD
VENT LINE
PRESSURE
RELIEF FILL, BUILDUP
TO AND VENT VALVE
GAUGING SYSTEM PRESSURE PRES.
RELIEF CLOSING LIQUID VALVE
CONTAINER FLOW
CONTROL REGULATOR VALVE PRES.
EVAPO- BUILDUP
RATING COIL
COIL CHECK ASSEMBLY • VALVE J
EMERGENCY
SHUTOFF VALVE FIGURE 786-2 TYPICAL LIQUID OXYGEN SYSTEM - USING COMBINATION VALVE AC 27-1A 1109
787. HOUR METERS OR TIME-IN-SERVICE RECORDING DEVICES IN ROTORCRAFI.
a. Explanation.
(1) Time in service is a required maintenance record according to § 91.173(a)(2)(i). Manual recording (rather than automatic) of the rotorcraft time in service is required whether or not the rotorcraft is equipped with a time accumulating device or hour meter. Time recording devices (hour meters) are optional and not required by the maintenance or operating rules or as a part of the aircraft type design.
(2) Time in service is defined in FAR Part 1 as follows: " ...with respect to maintenance time records, means the time from the moment an aircraft leaves the surface of the earth until it touches it at the next point of landing."
(3) The allowable total time in service, that is, service life or retirement time, has been typically specified for critical rotorcraft components that were subject to fatigue. The life was determined under § 27.571 or its predecessor standards.
(4) Hour meters may be mechanical and a part of a recording tachometer.
They may be electrical and activated by the main battery switch, engine oil pressure, or some other source. These devices may not record "real time" when an engine or rotor is at idle speed or when deactivated by an oil pressure sensor switch. This real time omission is not considered significant in the life of a rotorcraft if the design and installation of the sensor minimizes this omission. However, for an individual aircraft that is used extensively, the omission of real time may become significant, and the time in service should be adjusted prior to recording the time in service in the aircraft records.
b. Procedures.
(1) Time in service must be recorded in the aircraft maintenance records.
(2) Hour meters are used to accumulate operating time. The meters may be activated by various sensors/switches. The type design data should include hour meter installation data including the sensor/switch location and any adjustment or "rigging" information to ensure proper installation.
(3) One acceptable installation of a sensor/switch would activate the hour meter whenever the collective pitch control was moved from the lowest pitch stop position. That is, real time in service was recorded whenever the collective control was moved from the "full down" collective position.
The location of the sensor is important to ensure time in service is measured when collective lift or thrust of the main rotor is desired.
1110 Par 787
Time in service will not be accumulated in flight whenever full down (or near full down) collective is used, such as in some phases of autorotation.
However, collective controls are used to maintain proper rotor speed during autorotation.
(I) Time in service should be corrected (increased) for individual aircraft whenever "full down" collective is used a significant amount.
(4) If the hour meter installation is significantly deficient in recording real time in service, corrections must be made or the installation changed to eliminate any significant deficiency in the correct time in service.
Par 787 1111
АС 27-1A 7/30/97
788. Amendment 27-30) SUBSTANTIATION OF COMPOSITE ROTORCRAFT
STRUCTURE
a. Reference FAR Sections §§ 27.305, .307, .571, .603, .605, .609, .610, .611, .613, .629, .923, .927, .931, .1529 and Appendix A.
b. Purpose. These substantiation procedures provide a more specialized supplement to the general procedures outlined by AC 20-107A, "Composite Aircraft Structure." These procedures address substantiation requirements for composite material system constituents, composite material systems, and composite structures common to rotorcraft. A uniform approach to composite structural substantiation is desirable, but it is recognized that in a continually developing technical area which has diverse industrial roots, both in aerospace and in other industries, some variations and deviations from the procedures described herein will be both necessary and acceptable. Significant deviations from this material should be coordinated in advance with the Rotorcraft Directorate.
c. Special Considerations. Since rotorcraft structure is configured uniquely and is inherently subjected to severe cyclic stresses, special consideration is required for the substantiation of all rotorcraft structure, including composites. This special consideration is necessary to ensure that the level of safety intended by the current regulations is attained during the type certification process for all structure with special emphasis on composite structure because of its unique structural characteristics, manufacturing quality and operational considerations, and failure mechanisms.
d. Background.
(1) Historically, rotorcraft have required unique, conservative structural substantiation because of unique configuration effects, unique loading considerations, severe fatigue spectrum effects, and the specialized comprehensive fatigue testing required by these effects. Rotorcraft structural static strength substantiation for both metal and composite structure is essentially identical to that for fixed wing structure once basic loads have been determined. However, rotorcraft structural fatigue substantiation for metals is significantly different from fixed wing fatigue substantiation.
Since AC 20-107A, as developed, applies to both fixed wing aircraft and rotorcraft; it, of necessity, was finalized in a broad generic form. Accordingly, a need to supplement AC 20-107A for rotorcraft was recognized during type certification programs. One significant difference in traditional rotorcraft fatigue substantiation programs and fixed wing fatigue programs is the use of multiple full-scale specimen fatigue tests for rotorcraft programs rather than just one full-scale specimen test. Also, constant amplitude, accelerated load tests are typically used rather than spectrum tests because of the high frequency loads common to rotorcraft operations. These rotorcraft fatigue tests have traditionally involved the generation of stress versus life or cycle (S-N) curves for each critical part (most of which are subjected to the cyclic loading of the 1112 Par 788