AC 27-1B, Chg 7 2/4/2016
Page D - 124 (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.
(iii) 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 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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Page D - 126 (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 squib 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 - 127 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 RLCs 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 RLCs, a pin can be used to lock the hook keeper in place during operations.
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Page D - 128 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.
(iii) 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 fully 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.
AC 27-1B, Chg 7 2/4/2016
Page D - 130 ( 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.
( iii) 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.
( ii) Static strength. The PCDS should be substantiated for the allowable ultimate load and loading conditions as determined under paragraph d.(6) above.
( iii) Fatigue. The PCDS should be substantiated for fatigue as determined under paragraph d.(6) above.
(i v) 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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(D) Any fabric used should be durable and should be at least flameresistant.
(E) Safety harnesses and belts should meet TSO C167 requirements.
(F) Occupant retention devices and related design safety features should be used as necessary. In simple designs, rounded corners and edges with adequate strapping (or other means of HEC retention relative to the PCDS) and head supports or pads may be all the safety features that are necessary. However, in more complex PCDS designs, safety features such as seat belts, handholds, shoulder harnesses, placards, or other personnel safety standards may be required.
(v) EMI and lightning protection. All essential, affected components of the PCDS, such as intercommunication equipment, should be protected against RF field strengths to a minimum of RTCA Document DO-160 Category Y.
(v i) Instructions for continued airworthiness. All instructions and documents necessary for continued airworthiness, normal operations, and emergency operations should be completed, reviewed, and approved during the certification process. There should be clear instructions to describe when the PCDS is no longer serviceable and should be replaced in part or as a whole due to wear, impact damage, fraying of fibers, other forms of degradation. In addition, any life limitations resulting from compliance with paragraphs d.(10)(ii) and (iii) should be provided.
(vii) Flotation devices. PCDSs that are intended to have a dual role as floatation devices or life preservers should meet the requirements of TSO-C13f, "Life Preservers." Also, any PCDS design to be used in the water should have a floatation kit. The kit should support the weight of the maximum number of occupants and the PCDS in the water and minimize the possibility of the occupants floating face down.
(viii) Flight testing . It should be shown by flight tests that the device is safely controllable and maneuverable during all requested flight regimes without requiring exceptional piloting skill. The flight tests should entail the PCDS weighted to the most critical weight. Litters and other types of PCDS designs may spin, twist or otherwise respond unacceptably in flight. These designs should be structurally restrained with devices such as a spider, a harness, or an equivalent device to minimize undesirable flight dynamics.
(i x) Medical design considerations. The PCDS should be designed to the maximum practicable extent and placarded to maximize the HECs protection from medical considerations such as blocked air passages induced by improper body configuration and excessive loss of body heat during operations. Injured or water soaked persons may be exposed to high body heat loss from sources such as rotor wash and the airstream. PCDS occupant safety from transit induced medical considerations can be greatly increased by proper design.
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(x) Hoist operator safety device. When hoisting operations require the presence of a hoist operator on board, appropriate provisions shall be provided to allow the hoist operator to perform his task safely. These provisions shall include an appropriate hoist operator restraint system. This safety device is typically composed of a safety harness and a strap attached to the cabin used to adequately restrain the hoist operator inside the cabin while operating the hoist. For certification approval, the hoist operator safety device should comply with § 27.561(b)(3) for personnel safety. The applicant should submit a design evaluation that assures the necessary level of personnel safety is provided. The safety harness and strap should meet the requirements of TSO C22g, TSO C114, or TSO C167; however, as a minimum, the following should be evaluated:
(A) The strap attaching point on the body harness should not be located in the back of the hoist operator due to safety issues in case of a fall or crash.
(B) The safety device should be design ed to be adjustable so that the strap is tightened behind the hoist operator.
(C) The strap might include a QRS including a DAD to allow hoist operator detaching from cabin in emergency conditions (e.g., crash).
(D) The safety device should be easily and readily ingressed or egressed.
(E) It should be placarded for proper capacity and lifetime limitation.
(F) Any fabric used should be durable and should be at least flame resistant.
(11) Section 27.865(c)(4) Intercom Systems for HEC Operations. For all HEC operations, the rotorcraft is required to be equipped for, or otherwise allow direct intercommunication under any operational conditions among crewmembers and the HEC. An intercommunications system may also be approved as part of the external load system, or alternatively a limitation may be placed in the RFM or RFMS as described under paragraph d.(4)(ii)(B)(2) of this guidance).
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(12) Section 27.865(e) External Loads Placards and Markings. Placards and markings should be installed next to the external load attaching means, in a clearly noticeable location, that state the primary operational limitations - specifically including the maximum authorized external load. Not all operational limitations need be stated on the placard (or equivalent markings) only those clearly necessary for immediate reference in operations. Other more detailed operational limitations of lesser immediate importance should be stated either directly in the RFM or in a RFMS.
(13) Other Considerations.
(i) Agricultural Installation (AI). AIs can be approved for either jettisonable or non-jettisonable NHEC or HEC operations as long as they meet relevant certification and operations requirements and follow appropriate compliance methods. However, most current AI designs are external fixtures (see definition) - not external loads.
External fixtures are not approvable as jettisonable external cargo because they do not have a true payload (see definition), true jettison capability (see definition), or a complete QRS. Many AI designs can dump their solid or liquid chemical loads by use of a "purge port" release over a relatively long time period (i.e., greater than 30 seconds).
This is not considered true jettison capability (see definition) since the external load is not released by a QRS and since the release time span is typically greater than 30 seconds (see paragraph c.(21)). Thus, these types of AIs should be approved as a non-jettisonable external load. However, other designs that have the entire AI (or significant portions thereof) attached to the rotorcraft, that have short time frame jettison (or release) capability provided by a QRS that meets the definitions herein and that have no post-jettison characteristics that would endanger continued safe flight and landing may be approved as a jettisonable external load. For example, if all the relevant criteria are properly met, a jettisonable fluid load can be approved as a NHEC external cargo. Section AC 27 MG 5 of this AC discusses other AI certification methodology.
(ii) External Tanks. External tank configurations that have true payload (see definition) and true jettison capability (see definition) should be approved as jettisonable NHEC. External tank configurations that have a true payload capability but do not have true jettison capability should be approved as non-jettisonable NHEC. An external tank that has neither a true payload capability nor true jettison capability is an external fixture; it should not be approved as an external load under § 27.865. If an external tank is to be jettisoned in flight, it should have a QRS that is approved for the maximum jettisonable external tank payload and is either inoperable or is otherwise rendered reliable to minimize inadvertent jettisons above the maximum jettisonable external tank payload.
(iii) Logging Operations. These operations are very susceptible to low-cycle fatigue because of the large loads and relatively high load cycles that are common to this industry. It is recommended that load-measuring devices (such as load cells) be used to assure that no unrecorded overloads occur and to assure that cycles producing high fatigue damage are properly considered. Cycle counters are recommended to
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Page D – 132.2 assure acceptable cumulative fatigue damage levels are identifiable and are not exceeded. As either a supplementary method or alternate method, maintenance instructions should be considered to assure proper cycle counting and load recording during operations.
(14) Noise Certification. 14 CFR part 36 is the noise certification standard.
Section 36.1(a)(4) specifically exempts helicopters that are designed exclusively for agricultural work, carrying firefighting materials, or external loads activity from the noise standards. Section 21.93(b)(4) also contains specific information regarding external loads and what configurations do not constitute an acoustical change.
SUBPART D - DESIGN AND CONSTRUCTION
MISCELLANEOUS AC 27.871 § 27.871 LEVELING MARKS.
a. Explanation. Reference marks are required for leveling the rotorcraft on the ground. These marks are necessary for accurate determination of weight and balance effects, particularly after modifications to the basic rotorcraft.
b. Procedures.
(1) Reference marks are sometimes provided in pairs, one high in the cabin and one low. The plumb weight is suspended from the high mark by an appropriate mechanical attachment, and the lower mark is used to level the rotorcraft by centering the plumb weight. The lower reference mark should be a raised or depressed target symbol and shall be applied to a permanent structural component or permanently attached plate in a readily accessible location. Seat tracks, floors, or door sills which are attached with permanent fasteners are typical locations.
(2) Horizontal reference marks, for support of bubble levels, may also be used, particularly for smaller rotorcraft.
AC 27.873 § 27.873 BALLAST PROVISIONS.
a. Explanation.
(1) This rule requires that ballast provisions prevent inadvertent ballast shifting while in flight or as a result of a landing. Shifting of the ballast may cause a hazardous change in the center of gravity thereby affecting rotorcraft controllability.
(2) Other rules noted here allow removable and fixed ballast and require markings or placards to prevent overloading the ballast installation.
(i) Section 27.29 specifies that the rotorcraft empty weight will include any fixed ballast. Section 27.31 allows the use of removable ballast to comply with the flight requirements. However, ballast may not be adjusted (moved, reduced, or increased) in flight.
(ii) Section 27.1541 requires conspicuous and durable markings or placards. Section 27.1557 requires placards stating allowable maximum weight, distributed loading, if necessary, and other appropriate limitations for ballast installation.
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