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(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.
Page D - 113 (8 ) Hoist. A hoist is a device that exerts a vertical pull, usually through a cable and drum system (i.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 RLCs 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
AC 27-1B, Chg 7 2/4/2016 Page D - 114 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.
N ote: 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 (TIA). 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 - 115 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
AC 27-1B, Chg 7 2/4/2016
Page D - 116 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.
Page D - 117 Note: Some hoist designs have built-in cable tensioning devices that function at the no load-speed combination, as well as at other load-speed combinations. This device should work during the no load-speed and other load-speed cable-cutting demonstrations.
(E) Any devices or methods used to increase the mechanical advantage of the hoist should also be demonstrated.
(F) During a portion of each demonstration cycle, the hoist should be operated from each station from which it can be controlled.
(ii) Hoist and rescue hook systems or cargo hook systems flight test. An inflight demonstration test of the hoist system should be conducted for helicopters designed to carry NHEC or HEC. The rotorcraft should be flown to the extremes of the applicable maneuver flight envelope and to all conditions that are critical to strength, maneuverability, stability, and control, or any other factor affecting airworthiness.
Unless a lesser load is determined to be more critical for either dynamic stability or other reasons, the maximum hoist system rated load or, if less, the maximum load requested for approval (and the associated limit load data placards) should be used for these tests. The minimum hoist system load (or zero load) should also be demonstrated in these tests.
(iii) Section 27.865(d) Flight test Verification Work. Flight test verification work that thoroughly examines the operational envelope should be conducted with the external cargo carriage device for which approval is requested (especially those that involve HEC). The flight test program should show that all aspects of the operations applied for are safe, uncomplicated, and can be conducted by a qualified flight crew under the most critical service environment and, in the case of HEC, under emergency condition. Flight tests should be conducted for the simulated representative NHEC and HEC loads to demonstrate their in-flight handling and separation characteristics. Each placard, marking, and flight manual supplement should be validated during TIA flight testing.
(A) General. Flight testing or an equivalent combination of analysis , ground tests, and flight tests should be conducted under the critical combinations of configurations and operating conditions for which basic type certification approval is sought. The critical load condition of the intended cargo (e.g. rocks, lumber, radio towers, HEC) may be defined by a heavy weight and low area cargo or a low weight and high area cargo. The effects of these load conditions should be evaluated throughout the operational aspects of cargo loading, take-off, cruise up to maximum allowable speed with cargo, jettison, and landing. The helicopter handling with different cable conditions should include lateral transitions and quick stops up to the helicopter approved low airspeed limitations. Additional combinations of external load and operating conditions may be subsequently approved under relevant operational requirements as long as the structural limits and reliability considerations of the basic certification approval are not exceeded (i.e., equivalent safety is maintained). The
AC 27-1B, Chg 7 2/4/2016 Page D - 118 qualification flight test of this subparagraph is intended to be accomplished primarily by analysis or bench testing. However, at least one in-flight, limit load drop test should be conducted for the critical load case. If one critical load case cannot be clearly identified, then more than one drop test might be necessary. Also, in-flight tests for the minimum load case (i.e., typically the cable hook itself) with the load trailing both in the minimum and maximum cable length configurations should be conducted. Any safety-of-flight limitations should be documented and placed in the RFM or RFMS. In certain low-gross weight, jettisonable HEC configurations, the PCDS may act as a trailing airfoil that could result in entangling the PCDS and the rotorcraft. These configurations should be assessed on a case-by-case basis by analysis or flight test to assure any safety-of-flight limitations are clearly identified and placed in the RFM or RFMS (also see PCDS).
(B) Separation characteristics of jettisonable external loads. For all jettisonable RLC of any applicable cargo type, satisfactory post-jettison separation characteristics of all loads should meet the minimum criteria that follow:
(1) Separate functioning of the PQRS and BQRS resulting in a complete, immediate release of the external load without interference by the rotorcraft or external load system.
(2) No damage to the helicopter during or following actuation of the QRS and load jettisoning.
(3) A jettison trajectory clear of the helicopter.
(4) No inherent instability of the jettisonable (or just jettisoned) HEC or NHEC while in proximity to the helicopter.
(5) No adverse or uncontrollable helicopter reactions at the time of jettison.
(6) Stability and control characteristics after jettison within the originally approved limits.
(7) No adverse degradation on helicopter performance characteristics after jettison.
(C) Jettison requirements for jettisonable external loads. For representative cargo types (low, medium, and high density loads on long and short lines), emergency and normal jettison procedures should be demonstrated (by a combination of analysis, ground tests, and flight tests) at sufficient combinations of flight conditions to establish a jettison envelope that should be placed in the flight manual.
(D) QRS demonstration. Repetitive jettison demonstrations, which may be accomplished during ground or flight tests, should be conducted that use the PQRS.
The BQRS should be utilized at least once.
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(E) QRS reliability (i.e., failure modes) affecting flight performance. The FHA of the QRS (see paragraph d.(2) above) should show that any single system failure will not result in unsatisfactory flight characteristics, including any QRS failures resulting in asymmetric loading conditions.
(F) Flight test weight and CG locations. All flight tests should be conducted at the extreme or critical combinations of weight and longitudinal and lateral CG conditions within the applied for flight envelope. Typically the two load conditions would be a heavy weight and low area cargo, and a low weight and high area cargo.
The rotorcraft should remain within approved weight and CG limits both with the external load applied and after jettison of the load.
(G) Jettison Envelopes. Emergency and normal jettison demonstrations should be performed at sufficient airspeeds and descent rates to establish any restrictions for satisfactory separation characteristics. Both the maximum and minimum airspeed limits and maximum descent rate for safe separation should be determined.
The sideslip envelope as a function of airspeed should be determined.
(H) Altitude. Emergency and normal jettison demonstrations should be performed at altitudes consistent with the approvable operational envelope and with the maneuvering requirements necessary to overcome any adverse effects of the jettison.
(I) Attitude. Emergency and normal jettison demonstrations should be performed from all attitudes appropriate to normal and emergency operational usage.
Where the attitudes of HEC or NHEC with respect to the helicopter may be varied, the most critical attitude should be demonstrated. This demonstration would normally be accomplished by bench testing.
(4) Rotorcraft Flight Manual (RFM) and Rotorcraft Flight Manual Supplement (RFMS):
(i) General.
(A) Present appropriate flight manua l procedures and limitations for all HEC operations.
(1 ) Approval of an external loads equipment design in accordance with § 27.865 does not provide approval to conduct external loads operations. Therefore, the following shall be included as a limitation in the RFM or RFMS:
The external load equipment certification approval does not constitute operational approval; operational approval for external load operations must be granted by the local Aviation Authority.
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(2) The RFM or RFMS approved through the certification authority should not contain references to RLC classes, as this implies the design meets the operational rules.
(B) For non-HEC designs, the following limitation should be included within the RFM or RFMS:
The external load system does not comply with the 14 CFR part 27 certification requirements for Human External Cargo (HEC).
(C) The RFM or RFMS may contain wording to clarify whether the external load system meets the certification requirements for lifting an external load free of land or water and whether the load is jettisonable.
(D) The RFM or RFMS should contain emergency procedures detailing the steps to be taken by the flight crew during emergencies such as an engine failure, hoist failure, flight director or autopilot failure, etc.
(E) The RFM or RFMS normal procedures should explain the required procedures to conduct a safe external load operation. Such information may include the methods for attachment and normal release of the external load.
(ii) HEC installations.
(A) For HEC installations, the following additional limitations should be included in the RFM or RFMS.
(1) The external load system meets the 14 CFR part 27 certification requirements for Human External Cargo (HEC).
(2) Operation of the external load equipment with HEC requires the use of a Personnel Carrying Device Systems (PCDS), which must be approved by the local Aviation Authority. TSO-C167 provides one such acceptable means of approval.
(B) Crewmember communications.
(1) The flight manual should clearly define the method of co mmunication between the flight crew and the HEC. These instructions and manuals should be validated during TIA flight testing.
(2) If the external load system does not include equipment to allow direct intercommunication among required crewmembers and external occupants, the following limitation may be included within the limitations section of the RFM or RFMS:
Page D - 121 This external load system does not include equipment to allow direct intercommunication among required crewmembers and external occupants. Operating this external load equipment with HEC is not authorized unless equipment to allow direct intercommunication among required crewmembers and external occupants is approved by the local Aviation Authority.
(iii) Additional RFM or RFMS requirements are contained within each applicable paragraph of this guidance.
(5) Continued airworthiness.
(i) Instructions for Continued Airworthiness. Maintenance manuals (and RFM supplements) developed by applicants for external load applications should be presented for approval and should include all appropriate inspection and maintenance procedures. The applicant should provide sufficient data and other information to establish the frequency, extent, and methods of inspection of critical structure, systems, and components. 14 CFR 27.1529 and Appendix A to part 27 requires this information be included in the maintenance manual. For example, maintenance requirements for sensitive QRS squibs should be carefully determined, documented, approved during certification, and included as specific mandatory scheduled maintenance requirements that may require either "daily" or "pre-flight" checks (especially for HEC applications).
(ii) Hoist system continued airworthiness . The design life of the hoist system and any limited life components should be clearly identified, and the Airworthiness Limitations Section of the maintenance manual should include these requirements. For STCs, a maintenance manual supplement should be provided that includes these requirements.
Note: Design lives of hoist and cable systems are typically between 5,000 to 8,000 cycles. Some hoist systems have usage time meters installed. Others may have cycle counters installed. Cycle counters should be considered for HEC operations and high load or other operations that may cause low-cycle fatigue failures.
(6) Section 27.865(a) Static Structural and § 27.865(f) Fatigue Substantiation Procedures. The following static structural substantiation methods and fatigue substantiation procedures should be used:
(i) Critical basic load determination. The critical basic loads and corresponding flight envelope are determined by statically substantiating the gross weight range limits, the corresponding vertical limit load factors (NZW) and safety factors applicable for the type of external load for which the application is being made.
AC 27-1B, Chg 7 2/4/2016 Page D - 122 Note: In cases where NHEC or HEC can have more than one shape, center-of-gravity, center-of-lift, or be carried at more than one distance in flight from the rotorcraft attachment, a critical configuration for certification purposes may not be determinable. If such a critical configuration can be determined, it may be examined for approval as a "worst case" to satisfy a particular certification criterion or several criteria, as appropriate. If such a critical configuration cannot be determined, the extreme points of the operational – external load configuration envelope should be examined with consideration given to any other points within the envelope which experience or other rationale would indicate should be investigated.
(ii) Vertical Limit and Ultimate Load Factors. The basic NZW is converted to ultimate load by multiplying the maximum vertical limit load by the appropriate safety factor. (For restricted category approvals, see section AC 27 MG 5 of this AC.) This ultimate load is used to substantiate all existing structure affected by, and all added structure associated with, the load carrying device, its attachments and its cargo.
Casting factors, fitting factors, and other dynamic load factors should be applied where appropriate.
(A) NHEC applications. In most cases, it is acceptable to perform a standard static analysis to show compliance. A vertical limit load factor (NZW) of 2.5 g is typical for heavy gross weight NHEC hauling configurations (see section 27.337 of this guidance). This vertical load factor should be applied to the maximum external load for which application is being made, together with a minimum safety factor of 1.5.
(B) HEC applications.
(1) If a safety factor 3.0 or more is used, it is acceptable to perform a standard static analysis to show compliance. The safety factor should be applied to the yield strength of the weakest component in the system (QRS, PCDS, and attachment load path). If a safety factor of less than 3.0 is used, both an analysis and a full-scale ultimate load test of relevant parts of the system should be submitted.
(2) Since HEC applications typically involve lower gross weight configurations, a higher vertical limit load factor is required to assure that limit load is not exceeded in service. The applicant should use either the conservative value of 3.5 g or an analytically derived maximum vertical limit load factor for the requested operating envelope. Linear interpolation between the vertical load factors of maximum and minimum design weights may be used. However, in no case may the vertical limit load factor be less than 2.5 g for any RLC application for HEC.
(3) For the purpose of structural analysis or test, assume a 223-pound (101 Kg) man as the minimum weight of each occupant carried as HEC.
Page D - 123 Note: If the HEC is engaged in work tasks that employ devices of significant added weight (heavy backpacks, tools, fire extinguishers, etc.), the total weight of the 223-pound man and equipment should be assumed in the structural analysis or test.
(iii) Critical Structural Case. For applications involving more than one RLC class or cargo type, the structural substantiation is required only for the most critical case. The most critical case should be determined by rational analysis.
(iv) Jettisonable Loads. For the substantiating analyses or tests of all jettisonable RLC external loads, including HEC, the maximum external load should be applied at the maximum angle that can be achieved in service but not less than 30 degrees. The angle should be measured from the sling-load-line to rotorcraft vertical axis (z axis) and may be in any direction that can be achieved in service. The 30-degree angle may be reduced in some or all directions if it is impossible to obtain due to physical constraints or operating limitations. The maximum allowable cable angle should be determined and approved. The angle approval should be based on structural requirements, mechanical interference limits, and flight handling characteristics over the most critical conditions and combinations of conditions in the approved flight envelope.
(v) Hoist system limit load.
Note: In cases where hoist cables or long line cables are utilized, a new dynamic system is established. Characteristics of the system should be evaluated to assure that either no hazardous failure modes exist or that they are acceptably minimized. For example, the cable or long line may exhibit a natural frequency that could be excited by sources internal to the overall structural system (i.e., the rotorcraft) or by sources external to the system. Another example is the loading effect of the cable acting as a spring between the rotorcraft and the suspended external load.
(A) Determine the basic loads that result in the failure or unspooling of the hoist or its installation, respectively.
Note: This determination should be based on static strength and any significant dynamic load magnification factors.
(B) Select the lower of the two values as the ultimate load of the hoist system installation.
(C) Divide the selected ultimate load by 1.5 to determine the true structural limit load of the system.