(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 unsatistactory 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 manual procedures and limitations for all НЕС 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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AC 27-1B, Chg 7 2/4/2016
(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 communication 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:
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• 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
(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:
(1) 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.
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AC 27-1B, Chg 7 2/4/2016 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) НЕС 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.
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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.
(ili) 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.
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AC 27-1B, Chg 7 2/4/2016 (D) Determine the manufacturer's approved (or applicants applied for) "limit design safety factor." Divide this factor into the true structural limit load (from (C) above) to determine the hoist system's working (or placarded) limit load.
(E) Compare the system's derived limit load to the applied one "g payload multiplied by the maximum downward vertical load factor (NzwMAx) to determine the critical payload's limit value.
(F) The critical limit payload should be equal to or less than the system's derived limit load for the installation to be approvable.
(vi) Fatigue Substantiation Procedures (A) Fatigue evaluation of NHEC applications. Any critical components of the suspended system and their attachments (e.g., the cargo hook, or bolted or pinned truss attachments), the failure of which could result in a hazard to the rotorcraft, should include an acceptable fatigue analysis.
(B) Fatigue evaluation of HEC applications. The entire external load system, including the PCDS, should be reviewed on a component-by-component basis to determine which, if any, components are fatigue critical. These components should be analyzed or tested to assure their fatigue life limits are properly determined and placed in the limited life section of the maintenance manual.
(7) Section 27.865(b) and § 27.865(c) Procedures for Quick Release Systems.
For jettisonable RLCs of any applicable cargo type, both a primary quick-release system (PQRS) and a back-up quick-release system (BQRS) are required. Features that should be considered are:
(i) The PQRS, BQRS and their load release devices and subsystems (such as electronically actuated guillotines) should be separate (i.e., physically, systematically, and functionally redundant).
(ii) The controls for the PQRS should be installed on one of the pilot's primary controls, or in an equivalently accessible location. The use of an equivalent accessible location" should be reviewed on a case-by-case basis and used only where equivalent safety is clearly maintained.
(ill) The controls for the BQRS may be less sophisticated than that of the PQRS. For instance, manual cable cutters are acceptable provided they are listed in the flight manual as a required device and have a dedicated, placarded storage location.
(iv) The PQRS should release the external load in less than 5 seconds. The BQRS should release the external load in less than 30 seconds. This time interval begins the moment an emergency is declared and ends when the load is released.
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(v) Each quick-release device should be designed and located to allow the pilot or a crewmember to accomplish external cargo release without hazardously limiting the ability to control the rotorcraft during emergency situations. The flight manual should reflect the requirement for a crewmember and the related functions.
(vi) Section 27.865(c)(1) QRS Requirements for Jettisonable HEC Operations.
(A) For jettisonable HEC operations, both the PQRS and BQRS are required to have a DAD for external cargo release. The DAD must be designed to require two actions with a definite change of direction of movement, such as opening a switch or pushbutton cover followed by a definite change of direction in order to activate the release switch or pushbutton. Any possibility of opening the switch cover and inadvertently releasing the load with a single motion is not acceptable. An additional level of safety may also be provided through the use of Advisory and Caution messages. For example, an advisory "ON" message might be illuminated when the pilot energizes (but not arms) the system with a master switch. A cautionary "ARMED" message would then illuminate when the pilot opens the switch guard. In this case, a possible unwanted flip of the switch guard would be immediately recognized by the crew. The switch design should be evaluated by ground or flight test. The RFM or RFMS should contain a clear description of DAD functionality to include the associated safety features, normal and emergency procedures, and applicable advisory and caution messages.
(B) The DAD is intended for emergency use during the phases of flight that the HEC is carried or retrieved. The DAD can be used for both NHEC and HEC operations. However, because it can be used for HEC, the instructions for continued airworthiness should be carefully reviewed and documented. The DAD can be operated by the pilot from a primary control or, after a command is given by the pilot, by a crewmember from a remote location. Additional safety precautions (such as a lockwire) should be considered for remote hoist console in the cabin. Any emergency release Any one prey ragate.
function provided by a remote hoist console must also be designed to protect against inadvertent activation during the hoist operation. If the backup DAD is a cable cutter, it should be properly secured, placarded and readily accessible to the crewmember intended to use it.
(vii) Section 27.865(b)(3)(ii) Electromagnetic Interference. Protection of the QRS against potential internal and external sources of EMI and lightning is required.
This is necessary to prevent inadvertent load release from sources such as lightning strikes, stray electromagnetic signals, and static electricity.
(A) Jettisonable NHEC systems should be able to absorb a minimum of 20 volts per meter (i.e., CAT U) radio-frequency (RF) field strength per RTCA Document DO-160.
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AC 27-1B, Chg 7 2/4/2016 (B) Jettisonable HEC systems should be able to absorb a minimum of 200 volts per meter (i.e., CAT Y) RF field strength per RTCA Document DO-160.
(1) These RF field threat levels may need to be increased for certain special applications such as microwave tower and high voltage high line repairs.
Separate criteria for special applications under multi-agency regulation (such as IEEE or OSHA standards) should also be addressed, as applicable, during certification. When necessary, the issue paper process can be used to establish a practicable level of safety for specific high voltage or other special application conditions. The helicopter High-intensity Radiated Fields (HIRF) safety assessment should consider the effects on helicopter flight safety due to a HIRF-induced failure or malfunction of external load systems, such as uncommanded hoist winch activation without ability to jettison, or uncommanded load jettison. The appropriate failure effect classification should be assigned based on this assessment, and compliance demonstrated with § 27.1317 and the guidance in AC 20-158. This should not be limited to the cable cutter devices or load jettison subsystems only. In some designs, uncommanded load release or hoist winch activation could also result from a failure of the command and control circuits of the system.
(2) An approved standard rotorcraft test, which includes the full HIRF frequency and amplitude external and internal environments, on the QRS and any applicable PCDS, or the entire rotorcraft including the QRS and any applicable PCDS, could be substituted for the jettisonable NHEC and HEC systems tests as long as the RF field strengths directly on the QRS and PCDS are shown to equal or exceed those defined by paragraphs d. (7) (vii)(A) and d. (7)(vii) (B) above for NHEC and HEC respectively.
(3) The EMI levels specified in paragraphs d. (7)(vii)(A) and d. (7) (vii)(B) above are total EMI levels to be applied to the QRS (and affected QRS component) boundary. The total EMI level applied should include the effects of both external EMI sources and internal EMI sources. All aspects of internally generated EMI should be carefully considered including peaks that could occur from time-to-time due to any combination of on-board systems being operated. For example, special attention should be given to EMI from hoist operations that involve the switching of very high currents. Those currents can generate significant voltages in closely spaced wiring that, if allowed to reach some squib designs, could activate the device. Shielding, bonding, and grounding of wiring associated with operation of the hoist and the quick-release mechanism should be clearly and adequately evaluated in design and certification.
When recognized good practices for such installation are applied, an analysis may be sufficient to highlight that the maximum possible pulse generated into the squib circuit will have an energy contents' orders of magnitude below the squib no fire energy. If insufficient data is available for installation and/or squil no fire energy, this evaluation may require testing. One acceptable test method to demonstrate adequacy of QRS shielding, bonding, and grounding would be to actuate the hoist under maximum load together with likely critical combinations of other aircraft electrical loads and Page D - 126
demonstrate that the test squibs (that are more EMI sensitive than the squibs specified for use in the QRS) do not inadvertently operate during the test.
(viii) Section 27.865(c)(3) Placarding and marking. For jettisonable HEC applications, the associated QRS placarding should be given special consideration to assure the proper level of occupant safety.
(8) Cargo hooks or equivalent devices and their related systems. All cargo hooks or equivalent devices should be approved to acceptable aircraft industry standards.
The applicant should present these standards, and any related manufacturer's certificates of production or qualification as part of the approval package.
(i) General. Cargo hook systems should have the same reliability goals and should be functionally demonstrated under critical loads for NHEC and HEC, as appropriate. All engagement and release modes should be demonstrated. If the hook is used as a quick-release device, then release of critical loads should be demonstrated under conditions that simulate maximum allowable bank angles and speeds and any other critical operating conditions. Demonstration of any re-latching features and any safety or warning devices should also be conducted. Demonstration of actual in-flight emergency quick-release capability may not be necessary if the quick-release capability can be acceptably simulated by other means.
Notes: Cargo hook manufacturers specify particular shapes, sizes, and cross sections for lifting eyes to assure compatibility with their hook design (e.g., Breeze Eastern Service Bulletin CAB-100-41). Experience has shown that, under certain conditions, a load may inadvertently hang up because of improper geometry at the hook-to-eye interface that will not allow the eye to slide off an open hook as intended.
For both NHEC and HEC designs, the phenomena of hook dynamic roll-out (inadvertent opening of the hook latch and subsequent release of the load) should be considered to assure that QRS reliability goals are not compromised. This is of particular concern for HEC applications. Hook dynamic roll-out occurs during certain ground handling and flight conditions that may allow the lifting eye to work its way out of the hook.
Hook dynamic roll-out typically occurs when either the RLs sling or harness is not properly attached to the hook, is blown by down draft, is dragged along the ground or through water; or is otherwise placed into the dangerous hookto-eye configuration.
The potential for hook dynamic roll-out can be minimized in design by specifying particular hook-and-eye shape and cross-section combinations.
For non-jettisonable RLS, a pin can be used to lock the hook keeper in place during operations.
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AC 27-1B, Chg 7 2/4/2016 Some cargo hook systems may employ two or more cargo hooks for safety.
These systems are approvable. However, loss of any load by a single hook should be shown to not result in loss of control of the rotorcraft. In a dual hook system, if the hook itself is the quick-release device (i.e., if a single release point does not exist in the load path between the rotorcraft and the dual hooks), the pilot should have a dual PQRS that includes selectable, colocated individual quick releases that are independent for each hook used. A BQRS should also be present for each hook. For cargo hook systems with more than two hooks, either a single release point should be present in the load path between the rotorcraft and the multiple hook system, or multiple PQRS and BQRSs should be present.
(ii) Jettisonable cargo hook systems. For jettisonable applications, each cargo hook - (A) Should have a sufficient amount of slack in the control cable to permit cargo hook movement without tripping the hook release.
(B) Should be shown to be reliable (see paragraph d. (1)).
(C) For HEC systems, unless the cargo hook is to be the primary quick-release device, each cargo hook should be designed so that operationally induced loads cannot inadvertently release the load. For example, a simple cargo hook should have a one-way, spring-loaded gate (i.e., "snap hook") that allows load attachment going into the gate but does not allow the gate to open (and subsequently lose the HEC) when an operationally induced load is applied in the opposite direction.
For HEC applications, cargo hooks that also serve as a quick-release device should be carefully reviewed to assure they are reliable.
(ili) Other load release types. In some current configurations, such as those used for high line (or long line) operations, a load release may be present that is not on the rotorcraft but is a remote release system. The long lines allow the pilot to not release the line itself during repetitive loading operations. Examples are a tension release device that lets out line under an operationally induced load, a personal rope cutter or dedicated switches at the pilot controls. The release of the load through the secondary hook on a long line presents additional risks due to the possibility of the long line to impact the tail or main rotor after a release due to its elasticity. These devices are acceptable if the:
(A) off-rotorcraft release is considered a "third release." This type of release is not a substitute for a required release (i.e., PQRS or BQRS);
(B) cargo hook release, and the long line release are placed on the primary controls in a way to avoid confusion during operation. One example of compliance would be to place the cargo hook release on the cyclic and the long line release on the collective to avoid any possible confusion in the operation;
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(C) RFM or RFMS includes a description of the new control in the cockpit and its function and an RFM or RFMS note to the pilot is included indicating that the helicopter hook emergency release procedures are tully applicable;
(D) release meets the same certification reliability criteria adopted for the helicopter certified hook, as well as other relevant requirements of § 27.865 and the methods of this guidance or equivalent methods; and (E) release has no operational or failure modes that would affect continued safe flight and landing under any operations, critical failure modes, conditions, or combination of either. The following points should be considered:
(1) The long line should not be of an elastic material allowing spring up when unloaded or elevated dynamics when loaded.
(2) The long line should have a residual weight allowing its release from the helicopter hook when the long line is unloaded.
(3) The RFM or RFMS should include all operating procedures to ensure that the long line does not impact the rotors after cargo release and during unloaded flight phases.
(4) The hook should be designed to minimize inadvertent activation.
An example may be a protective device (cage) around the locking mechanism of the long line hook.
(5) A means should be provided to prevent fouling of cables in the event of rotation of the external load. An example may be the inclusion of a swivel or slipring.
(6) Installation of long line provided with electrical wiring to control the hook will generally represent a new electromagnetic coupling path from external area to the internal systems that may not have been considered for type certification. As such, the impact of this installation on the coupling to helicopter systems, due to direct connection or cross talk to wirings, must be addressed as part of compliance with §
27.610, 27.1316 and 27.1317.
(9) Cable
(i) Cable attachment. Either the cable should be positively attached to the hoist drum and the attachment should have ultimate load capability or equivalent means should be provided to minimize the possibility of inadvertent, complete cable unspooling.
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AC 27-1B, Chg 7 2/4/2016
(ii) Cable length and marking. A length of cable nearest the cable's attachment to the hoist drum should be visually marked to indicate to the operator that the cable is near full extension. The length of cable to be marked is a function of the maximum extension speed of the system and the operator's reaction time needed to prevent cable run out. It should be determined during certification demonstration tests.
In no case should the length be less than 3-1/2 drum circumferences.
(ili) Cable stops. Means should be present to automatically stop cable movement quickly when the system's extension and retraction operational limits are reached.
(10) Section 27.865(c)(2) PCDS. For all HEC applications, an approved PCDS is required. The PCDS may be either previously approved or is required to be approved during certification. A PCDS may also be approved after the external load system certification. Including a limitation in the RFM or RFMS requiring an approved PCDS will permit more flexibility for operators to utilize their own approved PCDS (see paragraph d. (4) of this guidance). In either case, its compatibility with the helicopter should be approved.
Note: PCDS designs can vary from simple single occupant lifesaving devices to relatively complex multiple occupant cages or gondolas. The purpose of the PCDS is to provide a minimum acceptable level of safety for personnel being transported outside the rotorcraft. The personnel being transported may be healthy or injured, conscious or unconscious.
(i) TSO C167 is an approved minimum performance specification for HEC body harnesses.
(il) Static strength. The PCDS should be substantiated for the allowable ultimate load and loading conditions as determined under paragraph d.(6) above.
(ili) Fatigue. The PCDS should be substantiated for fatigue as determined under paragraph d. (6) above.
(iv) Personnel safety. For each PCDS design, the applicant should submit a design evaluation that assures the necessary level of personnel safety is provided. As a minimum, the following should be evaluated.
(A) The PCDS should be easily and readily ingressed or egressed.
(B) It should be placarded for proper capacity, internal arrangement and location of occupants, and ingress and egress instructions.
(C) For door latch fail-safety, more than one fastener or closure device should be used. The latch device design should provide direct visual inspectability to assure it is fastened and secured.
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