(D) Any fabric used should be durable and should be at least flameresistant.
(E) Safety harnesses and belts should meet TSO C167 requirements.
(F) Occupant retention devices and related design safety features should be used as necessary. In simple designs, rounded corners and edges with adequate strapping (or other means of HEC retention relative to the PCDS) and head supports or pads may be all the safety features that are necessary. However, in more complex PCDS designs, safety features such as seat belts, handholds, shoulder harnesses, placards, or other personnel safety standards may be required.
(v) EMI and lightning protection. All essential, affected components of the PCDS, such as intercommunication equipment, should be protected against RF field strengths to a minimum of RTCA Document DO-160 Category Y.
(vi) Instructions for continued airworthiness. All instructions and documents necessary for continued airworthiness, normal operations, and emergency operations should be completed, reviewed, and approved during the certification process. There should be clear instructions to describe when the PCDS is no longer serviceable and should be replaced in part or as a whole due to wear, impact damage, fraying of fibers, other forms of degradation. In addition, any life limitations resulting from compliance with paragraphs d. (10)(ii) and (iii) should be provided.
(vii) Flotation devices. PCDSs that are intended to have a dual role as floatation devices or life preservers should meet the requirements of TSO-C13f, "Life Preservers." Also, any PCDS design to be used in the water should have a floatation kit. The kit should support the weight of the maximum number of occupants and the PCDS in the water and minimize the possibility of the occupants floating face down.
(vili) Flight testing. It should be shown by flight tests that the device is safely controllable and maneuverable during all requested flight regimes without requiring exceptional piloting skill. The flight tests should entail the PCDS weighted to the most critical weight. Litters and other types of PCDS designs may spin, twist or otherwise respond unacceptably in flight. These designs should be structurally restrained with devices such as a spider, a harness, or an equivalent device to minimize undesirable flight dynamics.
(ix) Medical design considerations. The PCDS should be designed to the maximum practicable extent and placarded to maximize the HECs protection from medical considerations such as blocked air passages induced by improper body configuration and excessive loss of body heat during operations. Injured or water soaked persons may be exposed to high body heat loss from sources such as rotor wash and the airstream. PCDS occupant safety from transit induced medical considerations can be greatly increased by proper design.
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AC 27-1B, Chg 7 2/4/2016
(x) Hoist operator safety device. When hoisting operations require the presence of a hoist operator on board, appropriate provisions shall be provided to allow the hoist operator to perform his task safely. These provisions shall include an appropriate hoist operator restraint system. This safety device is typically composed of a satety harness and a strap attached to the cabin used to adequately restrain the hoist operator inside the cabin while operating the hoist. For certification approval, the hoist operator safety device should comply with § 27.561(b)(3) for personnel safety. The applicant should submit a design evaluation that assures the necessary level of personnel safety is provided. The safety harness and strap should meet the requirements of TSO C22g, TSO C114, or TSO C167; however, as a minimum, the following should be evaluated:
(A) The strap attaching point on the body harness should not be located in the back of the hoist operator due to safety issues in case of a fall or crash.
(B) The safety device should be designed to be adjustable so that the strap is tightened behind the hoist operator.
(C) The strap might include a QRS including a DAD to allow hoist operator detaching from cabin in emergency conditions (e.g., crash).
(D) The safety device should be easily and readily ingressed or egressed.
(E) It should be placarded for proper capacity and lifetime limitation.
(F) Any fabric used should be durable and should be at least flame resistant.
(11) Section 27.865(c)(4) Intercom Systems for HEC Operations. For all HEC operations, the rotorcraft is required to be equipped for, or otherwise allow direct intercommunication under any operational conditions among crewmembers and the HEC. An intercommunications system may also be approved as part of the external load system, or alternatively a limitation may be placed in the RFM or RFMS as described under paragraph d.(4)(ii)(B)(2) of this guidance).
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(12) Section 27.865(e) External Loads Placards and Markings. Placards and markings should be installed next to the external load attaching means, in a clearly noticeable location, that state the primary operational limitations - specifically including the maximum authorized external load. Not all operational limitations need be stated on the placard (or equivalent markings) only those clearly necessary for immediate reference in operations. Other more detailed operational limitations of lesser immediate importance should be stated either directly in the RFM or in a RFMS.
(13) Other Considerations.
(i) Agricultural Installation (AI). Als can be approved for either jettisonable or non-jettisonable NHEC or HEC operations as long as they meet relevant certification and operations requirements and follow appropriate compliance methods. However, most current Al designs are external fixtures (see definition) - not external loads.
External fixtures are not approvable as jettisonable external cargo because they do not have a true payload (see definition), true jettison capability (see definition), or a complete QRS. Many Al designs can dump their solid or liquid chemical loads by use of a "purge port" release over a relatively long time period (i.e., greater than 30 seconds).
This is not considered true jettison capability (see definition) since the external load is not released by a QRS and since the release time span is typically greater than 30 seconds (see paragraph c. (21)). Thus, these types of Als should be approved as a non-jettisonable external load. However, other designs that have the entire Al (or significant portions thereof) attached to the rotorcraft, that have short time frame jettison (or release) capability provided by a QRS that meets the definitions herein and that have no post-jettison characteristics that would endanger continued safe flight and landing may be approved as a jettisonable external load. For example, if all the relevant criteria are properly met, a jettisonable fluid load can be approved as a NHEC external cargo. Section AC 27 MG 5 of this AC discusses other Al certification methodology.
(II) External Tanks. External tank configurations that have true payload (see definition) and true jettison capability (see definition) should be approved as jettisonable NHEC. External tank configurations that have a true payload capability but do not have true jettison capability should be approved as non-jettisonable NHEC. An external tank that has neither a true payload capability nor true jettison capability is an external fixture; it should not be approved as an external load under § 27.865. If an external tank is to be jettisoned in flight, it should have a QRS that is approved for the maximum jettisonable external tank payload and is either inoperable or is otherwise rendered reliable to minimize inadvertent jettisons above the maximum jettisonable external tank payload.
(ill) Logging Operations. These operations are very susceptible to low-cycle fatigue because of the large loads and relatively high load cycles that are common to this industry. It is recommended that load-measuring devices (such as load cells) be used to assure that no unrecorded overloads occur and to assure that cycles producing high fatigue damage are properly considered. Cycle counters are recommended to Page D - 132.1
AC 27-1B, Chg 7 2/4/2016 assure acceptable cumulative fatigue damage levels are identifiable and are not exceeded. As either a supplementary method or alternate method, maintenance instructions should be considered to assure proper cycle counting and load recording during operations.
(14) Noise Certification. 14 CFR part 36 is the noise certification standard.
Section 36.1(a)(4) specifically exempts helicopters that are designed exclusively for tandards. Section 2193(pe) also contains specific information regarding external s, or external loads activity from the noise loads and what configurations do not constitute an acoustical change.
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SUBPART D - DESIGN AND CONSTRUCTION
MISCELLANEOUS AC 27.871 § 27.871 LEVELING MARKS.
a. Explanation. Reference marks are required for leveling the rotorcraft on the ground. These marks are necessary for accurate determination of weight and balance effects, particularly after modifications to the basic rotorcraft.
b. Procedures.
(1) Reference marks are sometimes provided in pairs, one high in the cabin and one low. The plumb weight is suspended from the high mark by an appropriate mechanical attachment, and the lower mark is used to level the rotorcraft by centering the plumb weight. The lower reference mark should be a raised or depressed target symbol and shall be applied to a permanent structural component or permanently attached plate in a readily accessible location. Seat tracks, floors, or door sills which are attached with permanent fasteners are typical locations.
(2) Horizontal reference marks, for support of bubble levels, may also be used, particularly for smaller rotorcraft.
AC 27.873 § 27.873 BALLAST PROVISIONS.
a. Explanation.
(1) This rule requires that ballast provisions prevent inadvertent ballast shifting while in flight or as a result of a landing. Shifting of the ballast may cause a hazardous change in the center of gravity thereby affecting rotorcraft controllability.
(2) Other rules noted here allow removable and fixed ballast and require markings or placards to prevent overloading the ballast installation.
(i) Section 27.29 specifies that the rotorcraft empty weight will include any fixed ballast. Section 27.31 allows the use of removable ballast to comply with the flight requirements. However, ballast may not be adjusted (moved, reduced, or increased) in flight.
(ii) Section 27.1541 requires conspicuous and durable markings or placards. Section 27.1557 requires placards stating allowable maximum weight, distributed loading, if necessary, and other appropriate limitations for ballast installation.
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(3) Section 27.1583(c) concerns Rotorcraft Flight Manual instructions and information about removable ballast or loading information. The instructions must be included in the operating limitations section of the flight manual to allow ready observance of the limitations.
b. Procedures.
(1) The ballast installation may be substantiated by analysis or by static test.
The design ultimate load may be derived from flight, landing, or minor crash conditions load factors specified in the rules. Substantiation by analysis will require use of the fitting factor prescribed by § 27.625 where appropriate. If static tests are to be conducted, a test plan should be prepared, submitted for evaluation, and agreed upon prior to the test.
(2) Ballast installations in the aft part of the fuselage and tail boom may be subject to significant landing condition angular inertia load factors as well as the usual linear load factors.
(3) Substantiation methods and procedures acceptable for the airtrame substantiation may be used for the ballast installation as well.
(4) Removable ballast will require attention to ensure the ballast is secured easily and properly and will remain secured under the appropriate ballast design load factor requirements. The flight manual instructions should be evaluated for compliance with § 27.1583(c) by flight test and airframe personnel.
(5) The installation must be designed and placarded or marked for the maximum allowable ballast load and for other appropriate loading limits. Normally compliance with § 27.1541 is accomplished with a drawing review by airframe personnel along with a MIDO or FSDO compliance and conformity inspection. An additional compliance inspection by airframe personnel can be conducted if desired.
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CHAPTER 2. PART 27
AIRWORTHINESS STANDARDS
NORMAL CATEGORY ROTORCRAFT
SUBPART E - POWERPLANT
POWERPLANT - GENERAL AC 27.901. § 27.901 (through Amendment 27-20) INSTALLATION.
a. Section 27.901(a)
(1) Explanation. Paragraph (a) provides a definition of parts of rotorcraft for which safety requirements are set forth under the general title, SUBPART E - POWERPLANT. These parts include not only major propulsion elements and power transmission components but also controls, instruments, safety devices, including fire protection and other devices to protect personnel, and critical flight structure in event of fires.
(2) Procedures. To ensure that no certification aspect is overlooked in establishing compliance, certification engineers should make at least an informal breakdown of all components of the rotorcraft, assigning responsibility to powerplant certification engineers of all items within the above definition. While this procedure is usually straightforward, the following items of FAA/AUTHORITY powerplant responsibility are listed to minimize questions regarding authority and responsibility.
Drive system components. All parts of the transmission, clutches, shafting, including the driveshafts (masts) of main and auxiliary rotors, powerplant cooling components, and powerplant instrumentation requirements under §§ 27.1305,
27.1337, 27.1543, 27.1549, 27.1551, 27.1553, 27.1555, and 27.1583.
NOTE: The division of responsibility between FAA/AUTHORITY airframe engineers and FAA/AUTHORITY powerplant engineers (in accordance with FAA/AUTHORITY practice) regarding the driveshaft is at the flange or spline interface between the driveshaft and the rotor hub. Rotor hubs, controls, blades, and associated components are the airframe engineers' responsibility. (Industry practice may not agree with this concept.)
(ii) Engines, except for mount structure.
(iii) Auxiliary power units, except for mount structure.
(iv) Combustion heaters, except for downstream ventilation air ducting, mixing, and distribution systems and for electrical aspects of controls and safety devices.
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(v) Water/alcohol or other fluid power augmentation systems.
(vi) Engine induction systems including induction icing and snow ingestion, and exhaust systems, including exhaust shrouds and drains.
(vii) All fuel systems, including those serving engines, auxiliary power units, combustion heaters, power augmentation systems, etc., and vents and drains for those systems.
(vili) Oil systems for engines, auxiliary power units, rotor drive transmissions, and gearboxes, including grease lubrication.
(ix) Cooling aspects of engines, rotordrive transmissions and gearboxes, and auxiliary power units.
NOTE: Electrical generating equipment and hydraulic component cooling may be the responsibility of the systems and equipment engineer provided agreement is established among responsible personnel.
(x) Rotor brakes, except hydraulic and electrical aspects and structural aspects of nonrotating brake components.
(xi) Fire protection, including firewalls, fire extinguisher systems, fire detector systems, flammable fluid lines, fittings, and shutoff valves. The powerplant engineer has responsibility for evaluating compliance with §§ 27.861 and 27.863 as it pertains to fuel and oil systems.
(xii) Engine and transmission cowling and covering, including latches.
(xili) Powerplant flexible controls.
(xiv) Powerplant accessories.
(xv) Pneumatic systems (engine bleed air) within the engine compartments, including shut-off valves and engine isolation features of bleed systems.
(xvi) Powerplant aspects of instrument markings and powerplant aspects of flight manuals, including limitations, normal and emergency procedures, engine performance; powerplant aspects of maintenance manuals, with emphasis on the limitations section of the manual and verification of the limitations established under § 27.1521.
b. Section 27.901 (b).
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(1) Explanation. Paragraph (b) requires that the various powerplant components and systems be investigated for general airworthiness.
(2) Procedures.
Each item of the powerplant area of responsibility should be shown to be suitable for its intended purpose and installed to operate satisfactorily and safely between normal inspections and overhauls. Accessories mounted on engine or transmission drive pads should be determined to be compatible with the pad limits, including fit and speed range, overhang moment loads, running torque and static torque. This latter term pertains to protection of the engine or transmission which drives the accessory from damage to be expected from malfunction of the accessory. This protection is usually supplied by providing a shear section in the accessory drive shaft designed to fail before exceeding the static torque limit of the engine or transmission driving component. Note that when evaluating the strength of the mechanical shear section, material allowables quoted in materials handbooks should not be used since these are minimum strength values. Shear sections should consider maximum strength values to be expected which are on the order of 130 percent of the minimum strength values. Also, it should be verified that design data for shear sections are dimensioned to limit the maximum diameter as well as the minimum diameter. Installation of starter-generators may also require verification that horsepower extraction limits are not exceeded. Special flightcrew instructions in the flight manual to monitor generator load or to disconnect electrically loaded items to protect accessory or engine-transmission pad limits should be avoided.
(її) Environmental qualification requires consideration or protection against adverse effects of extremes of cold weather, salt and sand/dust atmosphere, altitude effects, etc. Most powerplant components are subjected to many of these aspects during the individual qualification tests; however, satisfactory overall integrated system performance under these adverse conditions must be verified. Cold weather testing should include verification that lubricating oils and greases function properly, and that engine starting procedures are safe and do not impose excessive loads on accessories, engines, or drive system components. Powerplant engineers should coordinate compliance efforts in this area with system engineer's investigations of compliance with §§ 27.1301 and 27.1309. Full-scale rotorcraft operations in cold weather should be required, including at least some exposure in the range of -10° to -20° F if the aircraft is to be certified to these ambients. Cold soak or overnight exposure to cold weather is appropriate followed by starting and pre-takeoff procedures in accordance with the flight manual. Attention should be given to the practicality of important mandatory inspection procedures as affected by cold weather.
(ili) Accessibility for maintenance should be reviewed. Typically, some maintenance activities must involve disassembly or removal of adjacent components.
This should be avoided if repetitive activity can jeopardize the performance of critical or safety-related equipment. Verify that easy access exists to items such as oil system Page E - 3
sight gauges or dip sticks, filler ports and drain valves for engines, auxiliary propulsion units, transmissions, fuel tanks and filters, etc.
(iv) Electrical interconnections to prevent difference of potential should be provided in the form of grounding straps or wires sized to carry the currents to be expected. Verify that the attachments for these grounding devices are not compromised by paint or zinc chromate which will tend to electrically insulate the engine or component. Note that engine mount structure should not be accepted as a grounding device since electrical current will cause corrosion at attach points.
(V) Axial and radial expansion of turbine engines is usually not a problem unless redundant mount arrangements are used. Special expansion provisions are usually required if engine components other than mounting points are attached to bulkheads, firewalls, other engines, or drive system components. Engine output shaft axial or bending loads due to thermal expansion and to deflection of supports under ground or flight loads should be checked. Other components of concern are compressor inlet flanges, exhaust ducts, and rigid fluid or air lines between aircraft structure and the engine. The engine installation data will provide limit loads to be considered for parts of the engine which normally are attached to airframe components.
c. Section 27.901(c).
(1) Explanation. Paragraph (c), in conjunction with the installation manual requirements of § 33.5, is intended to assure compliance with the detail installation requirements developed by the engine manufacturer to assure safe, continued operation of the engine.
(2) Procedure. Compliance with most of the detail requirements in the engine installation manual can be established by test or by design features and arrangements negotiated between the rotorcraft manufacturer and the FAA/AUTHORITY powerplant engineer. Some aspects, usually involving inlet and/or exhaust distortion limitations, vibration limitations and aircraft/engine interface items may require direct assistance and information from the engine manufacturer to determine that compliance with the installation manual exists. Fuel control/engine/rotor system torsional matching is usually a developmental problem to be worked out before presentation of the rotorcraft to the FAA/AUTHORITY; however, final flight tests for surge or stall, torsional stability, and acceleration/ deceleration schedules may require direct coordination among FAA/AUTHORITY installation engineers, engine manufacturers' representatives, and the FAA/AUTHORITY engine certification engineers. Reciprocating, carburetor equipped engines usually require a particular carburetor configuration to achieve adequate engine cooling. This configuration, identified as a "carburetor parts list," must be approved for the engine under Part 33 and should be listed on the type data sheet for the rotorcraft.
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AC 27.901A. § 27.901 (Amendment 27-23) INSTALLATION.
a. Explanation. Amendment 27-23 changes § 27.901(b)(1) to require a satisfactory determination that the rotorcraft can operate safely throughout adverse environmental conditions such as high altitude and temperature extremes. This amendment was needed to provide consistent application of the environmental qualification aspects of the installation. This amendment also added a new paragraph (§ 27.901(b)(5)) to require design precautions to minimize the potential for incorrect assembly of components and equipment essential to safe operation.
b. Procedures. All of the policy material pertaining to this section remains in effect with the addition of design precautions. Design precautions should be taken to minimize the possibility of improper assembly of the components essential to the safe operation of the rotorcraft. Fluid lines, electrical connectors, control linkages, etc., should be designed so that they cannot be incorrectly assembled. This can be achieved by incorporating different sizes, lengths, and types of connectors, wires, fluid lines, and mounting methods. The applicant should perform a detailed maintenance assessment to clearly define the maintenance requirements, reliability, and serviceability of the drive system design. The applicant should consider all design qualification tests and service history data, if available. A review of accident data supports the importance of this assessment. Some applicants have utilized drive system vibration monitoring to verify continuing safe operation of their drive system.
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