AC 27.861 § 27.861 FIRE PROTECTION OF STRUCTURE, CONTROLS, AND OTHER PARTS.
a. Explanation.
(1) As stated in the rule, parts essential to a controlled landing that would be affected by a powerplant fire are to be protected so they can perform their essential functions for at least 5 minutes under any foreseeable powerplant fire condition.
(2) To achieve the objective of the rule, essential parts of the rotorcraft as defined by the rule are to be isolated from a powerplant fire by a firewall (§ 27.1191) or must be protected so they can perform their essential functions for at least 5 minutes under any foreseeable powerplant fire condition.
(3) Insufficient protection to provide enough time for a controlled landing would represent an unsafe feature or characteristic for the rotorcraft design.
(4) Section 27.1193(d) requires each cowling and engine compartment covering to be at least fire resistant. Also, § 27.1193(e) requires that each part of the cowling or engine compartment covering, subject to high temperature due to its nearness (proximity) to exhaust system parts or exhaust gas impingement, must be fireproof.
(5) In addition, § 27.1194 requires that all surfaces aft of and near powerplant compartments, other than tail surfaces not subject to heat, flames, or sparks emanating from a powerplant compartment, be at least fire resistant.
b. Procedures.
(1) If each part described in the rule is isolated completely by firewalls, compliance is obtainable.
(2) If each part described by the rule is made of fireproof material, such as steel, compliance is obtained.
(3) If any part described by the rule does not comply with AC 27.861b(1) or (2), it shall be proven that it will perform its function under the prescribed conditions.
Compliance may be demonstrated by the following criteria:
The parts shall have a positive margin of safety for the appropriate flight and landing condition, including appropriate engine power conditions, under any foreseeable powerplant fire condition. The time interval under consideration here is the time necessary to complete an emergency descent (as described in the flight manual) and landing from the maximum operating altitude for which certification is requested. In no case is the total time interval to be less than 5 minutes.
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The factors affecting the time interval should include the maximum height above the terrain, the maximum operating altitude, the flight manual recommendations for rate of descent, and a reasonable time for recognizing a powerplant fire.
(¡¡i) The factors affecting the change in physical characteristics (strength primarily, but stiffness may also be a factor) of the parts are the temperature of the part, time interval at the elevated temperature, size, and heat absorption or rejection.
(iv) The factors affecting the temperature of the part are location and distance from the fire and flames and temperature of the flames (2,000° F +50° F should be used unless proven to be inapplicable).
(v) The rule requires substantiations for any foreseeable powerplant fire condition. Each rotorcraft design is unique and an evaluation of each design is necessary to establish the fire and flight conditions under consideration.
(vi) A very brief and simple example of compliance noted here may be helpful. This example pertains to a single-engine rotorcraft with the engine mounted on top at the fuselage centerline. The engine is supported by all steel tubular mounts. The fuselage panel serves as a work deck as well as a firewall. A 15-minute duration is appropriate for this design. A representative panel of the firewall (deck) skin may be subjected to the autorotational flight loads and the landing load. A flame from an appropriate-sized burner, measuring 2,000° F +50° F at the skin surface, should impinge on the loaded panel for 15 minutes. The panel may deform but must remain intact and sustain the appropriate load. The flame should not penetrate the panel skin.
(vil) Other rotorcraft designs may have engines located on top of the fuselage under the main rotor. If cowls or firewalls do not isolate the rotors and essential controls, it must be determined by a rational analysis or by temperature measurement that the rotor and essential controls will perform their functions. Air flow through the rotor and factors noted in paragraphs AC 27.861b(3)(ii), (3)(iii), and (3) (iv) are important to an analysis.
AC 27.861A § 27.861 (Amendment 27-26) FIRE PROTECTION OF STRUCTURE, CONTROLS, AND OTHER PARTS.
a. Explanation.
(1) Amendment 27-26 revised the regulation to allow use of parts made from standard fireproof materials of known acceptable dimensions in areas affected by powerplant fires without further proof or qualification. Previously, the standard imposed a performance criteria regardless of the materials and part dimensions used.
(2) "Fireproof" and "fire resistant" are defined in FAR Part 1, § 1.1.
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b. Procedures.
(1) A part of acceptable geometry made of steel, or another fireproof material, may be used to comply with the standard.
(2) A material system, panel, or assembly would be equivalent to steel provided it successfully completes the flammability tests described in paragraph AC 27.861b(3)(vi), for Category B rotorcraft adjusted for the time period appropriate to the rotorcraft application.
(3) It is appropriate to further define "fire resistant." A material system, panel, or assembly would be equivalent to aluminum (fire resistant) if it successfully completes the following flammability test. Locate a specimen (approximately 8 inches square) of the material system panel, assembly, or part at approximately a 45° angle to a horizontal line. Apply the limit or normal operating load. Impinge a 2000 +150° F (1093 ‡ 83°C) flame on the article for at least 5 minutes duration. Flame penetration of the test article is not allowed. In addition, the part or component should be able to perform its intended function, as installed, during and after the test.
AC 27.863 § 27.863 (Amendment 27-16) FLAMMABLE FLUID FIRE PROTECTION.
a. Background.
(1) The development of § 27.863 can be traced through CARS 6.485 and 6.486, and subsequent Amendment 27-16.
(2) Investigation of several accidents disclosed evidence of in-flight fires caused by leakage of flammable fluids to ignition sources. The revisions to § 27.863 adopted by Amendment 27-16 require significantly more attention to overall fire protection and prevention.
b. Explanation.
(1) Prior to Amendment 27-16, this rule only required either a means to prevent ignition of flammable fluids or vapors or a means to control any resulting fire. Isolation of flammable fluids and vapors from ignition sources by shrouding or sealing was the normal method of compliance. With Amendment 27-16, the rule further requires the assumption that these means fail or are ineffective and a fire does occur. Means to minimize the consequence of these fires must be provided. Specifically identified considerations must include the flammability of any combustible or absorbing materials, electrical faults, malfunction of protective devices, and so forth.
(2) The rule does not require the entire rotorcraft to be a "designated fire zone."
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AC 27-1B, Chg 4 3/31/2014
c. Methods of Compliance.
(1) To minimize the probability of ignition of fluids and vapors after single failure of a component or systems, the following methods may be used:
Shroud and drain flammable fluid systems (including steel fluid lines, fittings, etc.) and provide the systems with fuel and vapor seals with respect to potential ignition sources (electrical wiring and equipment, hot bleed air lines, etc.).
(ii) Provide other effective separation, ventilation, or overheat shutdown devices, etc., to preclude ignition.
(iv) Place a restricting orifice in fluid pressure lines routed to instruments and transducers.
(v) Ensure fluid lines are not located so as to be subject to abrasion during normal operations. Cargo compartments should be evaluated for potential line damage due to cargo movement.
(2) To minimize hazards if ignition occurs:
Provide fireproof designs, firewall isolation, or equivalent means for critical structure, equipment, and personnel areas.
(i) Consider fire detection, extinguishment, shutoff valves, fire suppression systems, etc.
(3) In considering compliance, the actual protective measures may be related to the situation, considering the quantity and flammability characteristic of the fluid, the fire damage tolerance of the area, and the means available to the crew to minimize hazards from the fire. If action by the crew is necessary, a quick acting means (not necessarily fire detectors) must be provided to alert the crew in the event of a fire.
Details of any action required by the crew should be included in the Rotorcraft Flight Manual.
(4) Compliance with § 27.863(d) requires, a minimum, type design data defining each area where flammable fluids or vapors might escape.
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SUBPART D - DESIGN AND CONSTRUCTION EXTERNAL LOAD.
AC 27.865. § 27.865 (Amendment 27-11) EXTERNAL LOAD ATTACHING MEANS.
a. Explanation.
(1) If certification for external load operations is requested, the rule requires that the external load attaching means be substantiated by test or analysis for a limit static load equal to or greater than 2.5 times the maximum external load for which certification is requested. The factor of 2.5 times the maximum external load was established as a minimum strength requirement by Part 133 operations to account for loading effects of sling-load angles up to 30° from the vertical. Allowance for reducing the 30° angle is provided if substantiated.
(2) The rule requires that a quick-release device be installed on one of the pilot's primary controls so the pilot can quickly release the external load during an emergency situation. In addition, a backup manual mechanical control for the quick-release device is required to be readily accessible to either the pilot or another crewmember.
(3) The rule requires appropriate placards or markings stating the maximum authorized external load.
b. Procedures.
(1) The maximum external load for which authorization is requested should not exceed the rated capacity of the quick-release device. The quick-release device should be strength tested (with FAA/AUTHORITY witness) if it is not produced to a recognized industry or military standard.
(2) Substantiation of external loading requirements must include any direction making an angle of 30° (with the exception of directions having a forward component).
(reference § 27.865(a).)
The sling-load angle (i.e., the angle between the vertical direction and the sling-load cable supporting the external load) should not exceed an angle of 30° to minimize the cable tension load.
(ї¡) The 30° angle may be reduced if an operating limitation is established limiting external load operations to such angles for which compliance has been shown or if the reduced angle cannot be exceeded in service. The lesser angle should be substantiated by flight testing.
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AC 27-1B, Chg 2 4/25/06
(3) The external load releasing system is specified to include a quick release device installed on one of the pilot's primary controls. It is usually installed on the cyclic stick to allow the pilot to release the load with minimum distraction after maneuvering the load into the release position.
(4) A manual mechanical control for the quick-release device is specified to be installed and be readily accessible to the pilot or to another crewmember. A sufficient amount of slack should be provided in the control cable to permit complete cargo movement without tripping the cargo release.
AC 27.865A. § 27.865 (Amendment 27-26) EXTERNAL LOAD ATTACHING MEANS.
a. Explanation. Amendment 27-26 added two requirements to § 27.865:
(1) Section 27.865(a) is clarified to allow use of a design factor less than 2.5g's, for rotorcraft load combinations A, B, and C non-human external cargo applications provided the lower load factor is not likely to be exceeded by virtue of the rotorcraft characteristics and capability. That is, the rotorcraft design factors may be used for the cargo device system.
(2) Section 27.865(d) was added to clarify and specify the fatigue requirements for the external cargo attaching means.
b. Procedures. All of the policy material pertaining to this section remains in effect with the following additions:
(1) For § 27.865(a), if a design limit load factor less than 2.5g's is requested, the applicant should provide a rational analysis and/or a flight operations data base that clearly shows that the load factor requested is unlikely to be exceeded in service.
NOTE: § 27.337 (b) requires use of 2.0 g's as a minimum.
(2) § 27.865(d), all failures of the cargo attaching means (and the associated critical components) that are likely to be hazardous to the rotorcraft should be identified by an acceptable means, such as a Failure Mode Effect Analysis (FMEA). The critical components associated with these failure modes should receive a fatigue analysis and/or test to ensure that the likelihood of a failure occurring is minimized. In the majority of cases, an analysis using the methods of AC 27 MG 11, "Fatigue Evaluation of Rotorcraft Structure", will be sufficient. If any component has a service life and/or mandatory inspection these components and each mandatory life should be identified, approved, and placed in the airworthiness limitations section of the maintenance manual or Instructions for Continued Airworthiness. See paragraph AC 27.1529 for information on these manuals.
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AC 27.865B. § 27.865 (Amendment 27-36) EXTERNAL.
a. Background. The standards for external load attaching means for transport and normal category rotorcraft were originally contained in Subpart D--Airworthiness Requirements of 14 CFR part 133, "Rotorcraft External-Load Operations."
Amendment 29-12, issued in 1977, added a new § 29.865, which moved these airworthiness standards from part 133 to part 29. An identical transfer occurred in 1977 for part 27. Amendment 29-26, issued in 1990, clarified the intent of Amendment 29-12 but did not change it substantively. Transport categories A and B and normal category rotorcraft were initially used under part 133 operations, and after Amendment 133-6, restricted category rotorcraft were also included under part 133 operations. The carriage of persons external to the rotorcraft for hire first came about when a part 29 operator, exempt from part 133, transferred harbor pilots to and from ships by a hoist and sling. The exemption was granted to study the feasibility of passenger transfer outside of the cabin. Grant of the exemption was based, in part, on similar, prior operations that had been conducted in Europe and Africa, for hire, with helicopters approved by the appropriate authorities and, in part, on similar military and public helicopter operations, not for hire, in the U.S. Subsequently, Amendment 27-36, adopted in October 1999, established requirements for human external cargo (HEC).
This amendment also removed references to rotorcraft load combinations (RLCS), as RLC approval is granted through the part 133 operational authority. Amendment 133-9 provided for the limitations and conditions for transport of external loads other than class A, B, or C and the necessary, associated safety requirements. Part 27 rotorcraft are not eligible for RLC class D, because of the current restriction of § 133.45(e) that limits use of RLC class D to transport category A rotorcraft (under the performance limits prescribed in § 133.45(e)). In addition, the scope and thus the title of the standard have changed from "External load attaching means" to "External loads" to reflect the more comprehensive approach for external loads required to assure the proper level-of safety.
b. Explanation.
(1) This advisory material contains guidance for the certification of helicopter external load attaching means and load carrying systems to be used in conjunction with operating rules such as part 133, "Rotorcraft External Load Operations." Subpart D of part 133 contains supplemental airworthiness requirements. 14 CFR part 1 defines the four RLC classes that are operationally approved under part 133 operating rules and eligible for airworthiness certification (with the exception of RLC class D due to the restriction of § 133.45(e)(1)) under § 27.865. For further information, AC 133-1A, Rotorcraft External-Load Operations in Accordance with Federal Aviation Regulations Part 133," dated October 16, 1979, may be reviewed. In addition, section 27.25 of this AC addresses, in part, jettisonable external cargo. Part 133 does not define nor permit fast-rope operations (an operation in which a person is not attached to an external means by a PCDS). Therefore, the FAA cannot certificate installations for the purpose of fast-roping.
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AC 27-1B, Chg 7 2/4/2016
(2) Section 27.865 provides a minimum level of safety for normal category rotorcraft designs to be used with operating rules such as part 133. Certain aspects of operations such as microwave tower and high-line wirework may also be regulated separately by other Federal agencies such as DOE, EPA, and OSHA or by other international entities. For applications that could come under multiple agency regulation (or regulation by other entities), special certification emphasis will be required by both the applicant and the approving authority to assure all relevant safety requirements are identified and met. Potential additional requirements are noted herein.
(3) The airworthiness standard for external loads (§ 27.865) does not discern the difference between a crewmember and a compensating passenger when either are carried external to the rotorcraft. Both are considered HEC.
c. Definitions.
(1) Backup Quick-Release Subsystem (BQRS). The secondary or "second choice subsystem used to perform a normal or emergency jettison of external cargo.
(2) Cargo. The part of any RLC that is removable, changeable, and is attached to the rotorcraft by an approved means. For certification purposes,"cargo applies to HEC and nonhuman external cargo (NHEC).
(3) Cargo hook. A hook that can be rated for both HEC and NHEC. It is typically used by being fixed directly to a designated hardpoint on the rotorcraft.
(4) Dual actuation device (DAD). This is a sequential control that requires two distinct actions in series for actuation. One example is removal of a lock pin followed by a "then free" switch or lever activation for load release to occur.
(5) Emergency jettison (or complete load release). The intentional, instantaneous release of NHEC or HEC in a preset sequence by the quick release system (QRS) that is normally performed to achieve safer aircraft operation in an emergency.
(6) External fixture. A structure external to and in addition to the basic airframe that does not have true jettison capability and has no significant payload capability in addition to its own weight. An example is an agricultural spray- boom. These configurations are not "External Loads" approvable under § 27.865.
(7) External Load System. The entire installation related to the carriage of external loads to include not only the hoist or hook, but also the structural provisions and release systems. The PCDS is considered part of the external load system only when the system is approved for HEC.
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(8) Hoist. A hoist is a device that exerts a vertical pull, usually through a cable and drum system (l.e., a pull that does not typically exceed a 30-degree cone measured around the z-rotorcraft axis).
(9) Hoist demonstration cycle (or "one cycle"). The complete extension and retraction of at least 95 percent of the actual cable length, or 100 percent of the cable length capable of being used in service (i.e., that would activate any extension or retraction limiting devices), whichever is greater.
(10) Hoist load-speed combinations. Some hoists are designed so that the extension and retraction speed slows as the load increases or nears the end of a cable extension. Other hoist designs maintain a constant speed as the load is varied. In the latter design, the load-speed combination simply means the variation in load at the constant design speed of the hoist.
(11) Human external cargo (HEC). A person(s) that at some point in the operation is carried external to the rotorcraft.
(12) Nonhuman external cargo (NHEC). Any external cargo operation that at no time involves a person(s) carried external to the rotorcraft.
(13) Normal jettison (or selective load release). The intentional release, normally at optimum jettison conditions, of an NHEC.
(14) Personnel carrying device system (PCDS). A device or system that has the structural capability and features needed to safely transport occupants external to the rotorcraft during HEC operations. A PCDS includes, but is not limited to, life safety harnesses, and rigid baskets or cages either attached to a hoist or cargo hook or mounted to the rotorcraft airframe (see TSO C167).
(15) Primary Quick-Release Subsystem (PQRS). The primary or "first choice" subsystem used to perform a normal or emergency jettison of external cargo.
(16) Quick-release system (QRS). The entire release system for jettisonable external cargo, (i.e., the sum total of both the primary and backup quick-release subsystems). The QRS consists of all components including the controls, the release devices, and everything in between.
(17) Rescue hook (or hook). A hook that can be rated for both HEC and NHEC.
It is typically used in conjunction with a hoist or equivalent system.
(18) Rotorcraft-load combination (RLC). The combination of a rotorcraft and an external-load, including the external-load attaching means. The flight characteristic requirements for the different classes of RLs are contained in § 133.41. RLC classes are not part of FAA design approval (see § 27.865) or contained in the associated rotorcraft flight manual or rotorcraft flight manual supplement (see § 27.1581). RLC Page D - 113
AC 27-1B, Chg 7 2/4/2016 classes are designated within operational approval under Part 133 and require an approved rotorcraft-load combination flight manual under § 133.47.
(19) Spider. A spider is a system of attaching a lowering cable or rope or a harness to a NHEC (or HEC) RLC to eliminate unwanted flight dynamics during operations. A spider usually has four or more legs (or load paths) that connect to various points of a PCDS to equalize loading and prevent spinning, twisting, or other undesirable flight dynamics.
(20) True jettison capability. The ability to safely release an external load using an approved QRS in 30 seconds or less.
Note: In all cases, a PQRS should release the external load in less than 5 seconds.
Many PQRSs will release the external load in milliseconds, once the activation device is triggered. However, a manual BQRS, such as a set of cable cutters, could take as much as 30 seconds to release the external load. The 30 seconds would be measured starting from the time the release command is given and ending when the external load is cut loose.
(21) True payload capability. The ability of an external device or tank to carry a significant payload in addition to its own weight. If little or no payload can be carried, the external device or tank is an external fixture (see definition).
(22) Type inspection authorization (IA). This IS FAA Form 8110-1, used for authorizing official ground inspections and flight-tests necessary to fulfill the requirements for type certification or supplemental type certification. Order 8110.4 contains the criteria for TIA issuance.
(23) Winch. A device that can employ a cable and drum or other means to exert a horizontal (i.e., x-rotorcraft axis) pull. However, in designs utilizing a winch to perform a hoist function by use of a 90-degree cable direction change device (such as a pulley or pulley system), the winch system is considered a hoist and must comply with the hoist requirements.
d. Procedures. The following certification procedures are provided in the most general form. Where there are significant differences between the cargo types, these differences are highlighted.
(1) General Compliance Procedures for § 27.865. The applicant should clearly identify both the applicable cargo types (NHEC or HEC) and the jettison capability (jettisonable or non-jettisonable) for which application is being made. The structural loads and operating envelopes for each applicable cargo type should be determined and used to formulate the flight manual supplement and basic loads report. The applicant should show by analysis, test, or both, that the rotorcraft structure, the external load attachment means, and the PCDS, if applicable, meet the specific Page D - 114
requirements of § 27.865 and the other relevant requirements of part 27 for the proposed operating envelope.
Note: The approved maximum internal gross weight should never be exceeded for any approved HEC configuration (or simultaneous NHEC and HEC configuration).
(2) Reliability of the external load system, including QRS.
(i) The hoist, QRS, and rescue hook system should be reliable for all phases of flight and the applicable configurations for those phases (i.e., operating, stowed, or unstowed) for which approval is sought. The hoist should be disabled (or an overriding, fail-safe mechanical safety device such as either a flagged removable shear pin or a load-lowering brake should be utilized) to prevent inadvertent load unspooling or release during any extended flight phases in which hoist operation is not intended. Loss of hoist operational control should also be considered.
(ii) Any failure mode of the external load system (including QRS, hook and attachments to the rotorcraft) leading to a loss of the HEC should be considered a Catastrophic event in accordance with the safety objectives in section 27.1309 of this AC. Uncontrolled high speed descent of the hoist cable would fall into this category.
Failures leading to the loss of NHEC should be evaluated and considered to be at least a Major event in accordance with the safety objectives in section 27.1309 of this AC.
(iii) The reliability of the system should be demonstrated by completion and approval of the following:
(A) A functional hazard assessment (FHA) to determine the hazard severity of failures associated with the external load system. The effect of the flailing cable after a load release should be considered.
(B) A fault tree analysis (FTA) or equivalent to verify the hazard classification of the FHA has been met.
(C) A system safety assessment (SSA) to demonstrate compliance with the applicable certification requirements.
D) An analysis of non-redundant external load system components that make up the primary load path (e.g., beam, cable, hook), to demonstrate compliance with the applicable structural requirements.
(E) A repetitive test of all functional devices that cycles these devices under critical structural conditions, operational conditions, or a combination of both at least 10 times each for NHEC and 30 times for HEC. This is applicable to both primary and backup subsystems. It is assumed that only one hoist cycle will typically occur per flight. This rationale has been used to determine the 10 demonstration cycles for NHEC applications and 30 demonstration cycles for HEC applications. However, if a particular Page D - 115
AC 27-1B, Chg 7 2/4/2016 application requires more than one hoist cycle per flight, then the number of demonstration cycles should be increased accordingly by multiplying the test cycles with the intended higher cycle number per flight. These repetitive tests may be conducted on the rotorcraft or by using a bench simulation that accurately replicates the rotorcraft installation.
(F) An environmental qualification for the proposed operating environment.
This review includes consideration of low and high temperatures (typically -40F to +150F), altitudes to 12,000 feet, humidity, salt spray, sand and dust, vibration, shock, rain, fungus, and acceleration. The FAA has accepted the results from the appropriate rotorcraft sections of RTCA Document DO-160 for high and low temperature and vibrations. The environmental qualification will address icing for those external load systems installed on rotorcraft approved for flight into icing conditions.
(G) Qualification of the hoist itself to the appropriate electromagnetic interference (EMI) and lightning threat levels specified for NHEC or HEC, as applicable.
This qualification can occur separately or as part of the entire onboard QRS.
(3) Testing.
(i) Hoist system load-speed combination ground tests. The load versus speed combinations of the hoist should be demonstrated on the ground (either using an accurate engineering mock-up or a rotorcraft) by showing repeatability of the no loadspeed combination, the 50 percent load-speed combination, the 75 percent load-speed combination, and the 100 percent (i.e., system rated limit) load-speed combination. If more than one operational speed range exists, the preceding tests should be performed at the most critical speed.
(A) At least 1/10 of the hoist demonstration cycles (see definition) should include the maximum aft angular displacement of the load from the vertical, applied for under § 27.865(a).
(B) A minimum of six consecutive, complete operation cycles should be conducted at the system's 100 percent (i.e., system limit rated) load-speed combination.
(C) In addition, the demonstration should cover all normal and emergency modes of intended operation and should include operation of all control devices such as limit switches, braking devices, and overload sensors in the system.
(D) All quick disconnect devices and cable cutters should be demonstrated at 0 percent, 25 percent, 50 percent, 75 percent, and 100 percent of system limit load or at the most critical percent.
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