AC 27-1B, Chg 4 2/27/2014
(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
(i) On outside surface of filler box cover plate:
LIQUID OXYGEN (BREATHING) FILL ACCESS
(iii) On underside surface of filler box cover plate:
CAUTION - KEEP CLEAN, DRY, AND FREE FROM OILS
(iv) In prominent place when filler box is open, preferably near liquid oxygen drain valve:
DO NOT OPEN DRAIN VALVE UNTIL DRAIN HOSE
AND DRAIN TANK ARE CONNECTED (V) Other placards, such as one at the converter cautioning about the presence of liquid oxygen, may also be appropriate.
Z) Other installation criteria are given in Chapter 6 of AC 43.13-2, Acceptable Methods, Techniques, and Practices-Aircraft Alterations, and should be given consideration.
D) Precautions. The referenced Society of Automotive Engineers (SAE) report contains precautions peculiar to a liquid oxygen installation, and this material should be reviewed. It should also be emphasized that liquid oxygen equipment and the aircraft being serviced must be electrically grounded during servicing to prevent an accumulation of static electricity and discharge. The following considerations are included for special emphasis:
(1) System Cleanliness. The completed installation should be free of oil, grease, fuels, water, dust, dirt, objectionable odors, or any other foreign matter, both internally and externally prior to introducing oxygen in the system.
(2) Closures. Lines that need to be disconnected during rotorcraft maintenance checks or overhaul, due to the location of the converter within the rotorcraft, should be capped to prevent materials that are incompatible with oxygen from entering the system when the system integrity is broken. Caps that introduce moisture and tapes that leave adhesive deposits should not be used for these purposes. All Page MG 6 - 12
openings of lines and fittings should be kept securely capped until closed within the Installation.
(3) Degreasing. All components of the oxygen system should be procured for oxygen service use in an "oxygen clean" condition. Parts of the oxygen system, such as tubing, not specifically covered by cleaning procedures should be degreased using a vapor phase trichloroethane degreaser. Ultrasonics may be used in conjunction with vapor phase degreasing for the cleaning of components.
(4) Purging. The system should be purged with hot, dry 99.5 percent pure oxygen gas in accordance with the manufacturers recommendations after:
(i) Initial assembly of the oxygen system; and
(il) 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.
(5) Maintenance and Replacement. All parts of the oxygen system should be installed to permit ready removal and replacement without the use of special tools.
All tubing connections and fittings should be readily accessible for leak testing with a leak test compound formulated for leak testing oxygen systems and for tightening of fittings without removing surrounding parts.
(il) Gaseous Oxygen.
(A) General. This guidance is intended to supplement the existing guidance in AC 43.13-2, Chapter 6. If there are any differences within the two ACS, this guidance prevails since it pertains specifically to part 27 requirements.
(B) System Components.
(1) High Pressure Cylinders. Many installations utilize hospital type cylinders rather than aviation type cylinders. A concern with the hospital type cylinders is the yoke and the hard plastic washer that is commonly used with these cylinders. It is very difficult to properly attach these yokes since the rotorcraft provides a high vibration environment and no positive lock is provided. Leaks are a continuous problem with this configuration. Yokes are 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 shutoff valve and regulator. All cylinders should be DOT approved.
(L) LInes.
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AC 27-1B, Chg 4 2/27/2014
(i) General. Any lines that pass through potential fire zones should be stainless steel.
(il) High Pressure. Use of high pressure lines may be necessitated by the use of a pressure regulator that is remote from the cylinder. The intent is to locate the regulator as close as physically possible to the cylinder, and to minimize the use of fittings. Lines of 6-inch lengths are encouraged with 18-inch lengths being the maximum in unusual circumstances. Lines made of stainless steel are recommended.
(iiI) Low Pressure. Although lines may only be subjected to low pressures, if they are located behind upholstery or for any reason are not 100 percent visible during normal operation, they should be solid metal lines or high pressure flexible lines that conform to SAE 100R14A specifications for stainless braided hoses. Other oxygen lines, so called "green lines," should only be used in locations that are 100 percent visible during normal operation. 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 are not 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.
(i) High Pressure. Intercylinder connections are made with regular flared or flareless tube fittings with stainless steel. Usually fittings are of the same material as the lines. Mild steel or aluminum alloy fittings with stainless steel lines are discouraged. Titanium fittings should never be used because of a possible chemical reaction and resulting fire.
I 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 and 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.
(5) Regulators. The regulator should be mounted as close as possible to the cylinders (see paragraph b.(10)(i)(B)(8) of this guidance). If non-aviation qualified regulators are considered, their service history should be reviewed and careful Page MG 6 - 14
consideration given to the manufacturer's environmental qualification. Radio Technical Commission for Aeronautics Document D0-160 is a recognized and accepted standard for environmental considerations. As a minimum, consideration should be given to operation during altitude, temperature, and vibration extremes.
(6) 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.
(Z) 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. An example of an acceptable placard for this situation is:
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 properly and the range at which this determination was made recorded in the project file. The functional demonstration should include a 360° turn (clockwise and counterclockwise) to ensure no significant sections of signal blanking exist. The remainder of the emphasis on this equipment should be to ensure that operation of this equipment does not interfere with normal operation of any rotorcraft 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 approved data should document the approach of how this evaluation was conducted. See paragraph b. (6) for other curtain considerations.
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AC 27-1B, Chg 4 2/27/2014 *(13) EDMS. If required under an operating regulation, an FDMS (not to be confused with a flight data recorder (FDR) certificated under § 27.1459) may be comprised of a system or combination of systems that record a helicopter's flight performance and operational data. An FDR certificated under § 27.1459 and the appropriate operating rules would be acceptable to meet this requirement; however, an FDMS would not be adequate to meet the § 27.1459 requirement for an FDR. The FDMS should record digital or analog raw data, images, cockpit voice or ambient audio recordings, or any combinations thereof, according to a broadly defined set of parameters including information pertaining to the aircraft's state, condition, and system performance. This data can be used to perform post flight analysis and provide critical information to investigators in the event of an incident or accident as well as to promote operational safety. When used in conjunction with an FAA-approved flight operations quality assurance (FOQA) program, part 135 certificate holders would be required to collect flight performance and operational data that characterizes the state of the helicopter and its subsystems that the certificate holder determines is pertinent to its safety program. FDMS data should be recorded and stored on digital media, and when selecting a location to install the hardware device used for storing the data, consideration should be given to the potential for survival in the event of a crash. The system should receive electrical power from the helicopter's bus that provides the maximum reliability without jeopardizing service to essential or emergency loads, and capable of being operated continuously from the time power is applied to the aircraft until power is removed from the aircraft.
(i) Safety. The FDMS equipment should not, under normal or fault conditions, adversely affect the airworthiness of the systems to which it is interfaced or of other aircraft systems. The equipment should be installed in accordance with all applicable safety regulations. The equipment should be tested under the standards of RTCA DO-160F, "Environmental Conditions and Test Procedures for Airborne Equipment," or subsequent issue. The European Organization for Civil Aviation Equipment (EUROCAE) specification ED-14 may be used in lieu of RTCA DO-160. Additional crashworthiness testing may be conducted according to EUROCAE specification ED-155, "Minimum Operational Performance Specification for Lightweight Flight Recording Systemsi Equipment testing should be conducted to the categories most applicable to the aircraft type, and the location of the equipment to be installed. The equipment manufacturer typically defines the test class within each environmental category. The objective of this level of testing is to ensure that the equipment does not present a hazard to the aircraft, and can survive and continue to operate under the environmental conditions to which it will be subjected throughout its life. Specific testing may be required to demonstrate that the equipment performs its intended function when operated over the full environmental conditions to which it has been declared to comply.
Consideration should be given to the extremes at which it may be subjected during an incident or accident. These tests can be undertaken during the specified RTCA DO- 160F (or later revision) tests or separately. Analysis may be substituted for a test where its use can be shown to produce equivalent evidence of compliance. The system should be capable of recording up to 2 hours of image or acoustical data and 6 hours of Page MG 6 - 16
aircraft parameter data. The applicant determines and maintains the data stream format and parameter documentation, including which parameters are recorded, how often the parameters are recorded, the bit resolution of each parameter, the operational range of each parameter, and the conversion algorithm from decimal units to engineering units. The Design Assurance Level (DAL) for an FDMS that is required by an operating regulation is DAL "D." RTCA DO-178B (or later revision) provides acceptable software development standards, which in this case would be for DAL "D" software. RTCA DO-254 (or later revision) provides acceptable airborne electronic hardware (AEH) development standards, which in this case would be for DAL "D" AEH.
Note: The duration between data downloads for the promotion of operational safety within a FOQA program is directly correlated to the recording capabilities of the system installed.
(ii) Recording. The FDMS should be capable of capturing and recording any combination of the following parameters in order to monitor the aircraft's state, condition, and system performance:
• Positioning system time.
Positioning system latitude.
Positioning system longitude.
Positioning system altitude.
Positioning system error.
Altitude.
Heading.
Pitch attitude.
Pitch rate.
Roll attitude.
• Roll rate.
• Yaw rate.
• Air speed.
• Ground speed.
• Ambient acoustic data.
• Engine parameters.
• Main rotor revolutions per minute.
• Transmission ambient audio.
• Any other parameters deemed appropriate by the operator.
Notes: Parameters may be recorded directly or deduced from recorded data from the FDMS. Additional guidance on parameters can be found in EUROCAE specification ED-155.
Recording individual pilots, using hot microphones, on separate pilot audio channels can provide useful information in the investigation of incidents and accidents.
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AC 27-1B, Chg 4 2/27/2014
(ili) Maintenance. The maintenance requirements to ensure the serviceability and continued airworthiness of the FDMS are typically established by the equipment manufacturer and installer. These maintenance instructions should be included in the applicable helicopter model instructions for continued airworthiness.
*(14) Radio Altimeter (RAD ALT). RAD ALTs installation is required. Its information display must be in the pilot's primary field of view in all helicopters operating under a part 135 certificate. The minimum performance requirements for an FAA approved RAD ALT system can be found in TSO-C87.
(15) Other EMS Equipment. These items of equipment installed for the EMS mission are considered optional equipment and should be operated to ensure they function properly. This evaluation would normally be done by someone 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 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.
(16) Miscellaneous. The following areas are not peculiar to EMS installations;
however, their significance is enhanced by the complexity of an EMS installation.
(i) Compatibility. Many EMS installations are a collection of several STCs and may also include some FAA 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 addressed since in using this system it can be difficult to keep light from interfering with the pilot view.
(il) Electrical Load Analysis. An electrical load analysis should be conducted, and additional guidance is available in AC 27-1 MG 1. If the analysis indicates the generators) can be overloaded, appropriate measures should be taken to account for the problem. In some instances (e.g., in a visual flight rules (VFR) approved rotorcraft), a placard that specifies certain operating limitations may be satisfactory, while in other instances (e.g., in an instrument flight rules (IFR) approved rotorcraft), an electrical interlock may be in order. In general, if the amount of overload is relatively small and the rotorcraft is not an IF-approved rotorcraft, 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.
(ili) Aircraft Grounding. It should be emphasized in an appropriate place in the STC data (e.g., RFM, maintenance information) that any time the EMS systems are Page MG 6 - 18
being operated or serviced (e.g., oxygen) 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 (e.g., air, oxygen, vacuum) should be placarded. 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, non-accessible compartment. Also, the cargo weight limitations placard should be changed. AC 27-1, section 27.787 pertains to cargo and baggage compartments.
(vil) Safety Assessment. When installing any new equipment or modifying existing equipment, a safety assessment must be made to assure the FAA that all possible failure conditions that could occur from these changes have been adequately addressed to show compliance to the regulations.
(17) 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 (e.g., new model, manufacturer) is to be substituted, then an evaluation should be made to ensure 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 ensure there are no 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 Regulations and References.
(1) Regulatory Sections. 14 CFR 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,
27.1589, part 91, and part 135.
(2) Other References. Refer to the current version of each document.
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AC 27-1B, Chg 4 2/27/2014
(i) Helicopter Association International, Emergency Medical Services Recommended Guidelines.
(ii) National Highway Traffic Safety Administration, Air Ambulance Guidelines.
(iii) AC 23-2, Flammability Tests.
(iv) AC 43.13-2, Acceptable Methods, Techniques, and Practices-Aircraft Alterations.
(v) AC 135-14, Emergency Medical Services/Helicopter (EMS/H).
(vi) Oxygen Equipment for Aircraft, Society of Automotive Engineers Aerospace Information Report No. 825.
(vii) MIL-D-19326G, Design and Installation of Liquid Oxygen Systems in Aircraft, General Specification for Military Specification.
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INTEGRAL ASSEMELY 2/27/2014 (Most Cases) FIGURE AC 27.MG 6-1 TYPICAL LIQUID OXYGEN SYSTEM OVERBOARD
VENT LINE PRESSURE BUILDUP/VENT
RELIEF VALVE TO
GAUGENE C SYSTEM
PRESSURE
RELIEF CLOSING PRES, LIQUID VALVE
CONTAINER TO
PATIENT - CON TROI VALVE REGULATOR EVAPO PRES.
RATING COIL BUILDUP COIL CHECK I FILL VALVE
ASSEMBLY VALVE Page MG 6 - 21 EMERGENCY AC 27-1B, Chg 4
SHUTOFF VALVE
Page MG 6 - 22 INTEGRAL ASSEMBLY AC 27-1B, Chg 4 (Most Cases) FIGURE AC 27.MG 6-2 TYPICAL LIQUID OXYGEN SYSTEM - USING OVERBOARD
VENT LINE
PRESSURE
RELIEF FILL, BUILDUP
AND VENT VALVE TO
COMBINATION VALVE PRESSURE PRES
RELIEF CLOSING LIQUID
VALVE CONTAINER FLOW
CONTROL REGULATOR
WALVE PRES
EVAPO- BUILDUP
RATING COIL
COIL OHECK
ASSEMBLY VALVE EMERGENCY 2/27/2014
SHUTOFF VALVE
CHAPTER 3
AIRWORTHINESS STANDARDS
NORMAL CATEGORY ROTORCRAFT
MISCELLANEOUS GUIDANCE (MG) AC 27 MG 7. 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.
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