(2) The rule does not go so far as to require the entire rotorcraft to be a “designated fire zone.” Zonal analysis of areas containing flammable fluids may be used to show compliance with the requirements of this section. The general philosophy to be adopted for demonstrating compliance with § 29.863 is illustrated in AC 29.863-1.
c. Methods of Compliance.
(1) To minimize the probability of ignition of fluids and vapors after single failure of a component or systems, the following methods may be used. In considering compliance, the actual extent of protective measures required may be related to the situation considering the quantity and flammability characteristics of the fluid, the fire damage tolerance of the area, and the means available to the crew to minimize hazards from a fire.
(i) Shroud and drain flammable fluid systems (including steel fluid lines), fittings, etc. and/or provide fuel and vapor seals with respect to ignition sources (electrical wiring and equipment, hot bleed air lines, etc.). Drains should be designed and positioned to enable systems to be drained until any remaining flammable fluid residue is negligible. The arrangement of drains should be such that the discharge of flammable fluid from the outlet would not constitute a fire hazard, nor could flammable fluid or vapor enter personnel compartments or other portions of the rotorcraft where a hazard of ignition may exist. If flammable fluid drains are routed through personnel compartments, means for protection from damage should be provided to prevent possible entry of flammable fluids or vapors into these compartments.
(ii) Provide other effective separation, ventilation, or overheat shutdown devices, etc., to preclude ignition. System s using flammable fluids should be separated from potential sources of ignition, including equipment or parts with hot surface temperatures above the ignition temperature of the fluid, such that the risk of fires as a result of leakage or bursting of the fluid system is minimized.
(iii) Ensure that potential ignition sources, such as bleed air lines and electrical equipment in the areas subject to flammable fluids and vapors is either hermetically sealed, shrouded, insulated or ventilated as necessary to minimize the possibility of ignition, or has been tested and shown to be free of ignition capability.
(iv) Place a restricting orifice in fluid pressure lines routed to instruments and transducers.
(v) Ensure flammable fluid carrying lines and drain lines are not located so as to be subject to abrasion during normal operations. Cargo compartments should be evaluated for potential line damage due to cargo movement.
(2) To minimize the hazards if ignition occurs:
(i) Provide fireproof designs, fire wall isolation, or equivalent means for critical structure, equipment and personnel areas, e.g.:
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(A) Flammable fluid lines and reservoirs of flammable fluids should be adequately protected against the anticipated type and duration of fire should ignition occur. Drain lines and their fittings, the failure of which would not result in, or add to, a fire hazard need not be Fire-resistant.
(B) Where there is a risk of leaking flammable fluids re-entering the rotorcraft through joints in the cowling or other rotorcraft surfaces to areas where a hazard of ignition may exist, the ventilation of such compartments should, where practical, be arranged to provide an air pressure within the compartment higher than that of the pressure of the ambient air.
(C) Absorbent materials in areas where leakage or spillage of flammable fluids (i.e., liquids, vapors, gases) could occur as a result of normal operation, failures of the equipment, or leakage from joints or unions should be covered or treated to prevent the absorption of hazardous quantities of fluid. Whenever insulation made of absorbent materials is used on pipes, tanks or equipment containing Flammable fluids, suitable precautions should be taken to prevent the wetting of the insulation by Flammable fluids.
(D) All electrical equipment including cables and their accessories should, as far as is practicable, be constructed of material which do not support combustion and which meet the relevant requirements of FAR/JAR25 Appendix F Part 1. Other materials should be applied and/or protected so that the risk arising from a fire is not increased by their use.
(E) It should be shown by analysis and/or tests that there are adequate means to prevent hazardous quantities of smoke, flame, extinguishing agents or other noxious gases produced as a result of a fire from entering any crew or passenger compartment.
(F) All components of the overheat or fire detector system (if applicable) should be at least Fire resistant.
(G) If located in an area where flammable fluids are present, critical structural components, controls, and essential indicating systems required for safe flight must be able to withstand the conditions resulting from a flammable fluid fire in the area so that a safe landing may be made. Under these conditions the structural members and the control devices should be able to carry the loads appropriate to the expected maneuvers including any vibrations normally experienced in flight. The quantity of flammable fluid likely to be present assuming all fluid drains function correctly and the maximum temperature characteristics of the particular flammable fluid may be taken into account in the analysis of the effect of a fire on critical structure. When making the determination that these components can withstand the flammable fluid fire conditions, the time required to detect such a fire should be taken into account.
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(ii) In considering compliance, the actual protective measures required may be related to the situation considering the quantity and flammability characteristics of the fluid, the fire damage tolerance of the area, and the means available to the crew to minimize hazards from the fire. Provisions for fire detection, extinguishment, shutoff valves, fire suppression systems, etc., may be considered as alternate means to limit the duration of a fire in lieu of the protective measures listed in (2)(i) above. However, the consequences of spurious or erroneous operation of these systems should also be considered when evaluating the requirement for their provision. If action by the crew is necessary, quick-acting means (not necessarily fire detectors) should be provided to alert the crew in the event of a fire. Details of any action required by the crew must be in the Rotorcraft Flight Manual in accordance with § 29.1585(a).
(3) Compliance with § 29.863(d) requires as a minimum, type design data defining each area where flammable fluids or vapors might escape.
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Completed Design Review Are Systems Containing Flammable Fluids Present?
Could Ignition Sources Be Present, Before or After System/Component Failure?
No Yes Yes No Yes Could Flammable Fluids be Present After Leakage or Draining From Other Areas?
No FAR Section 29.863 Not Applicable No Hazard Minimize the Probability of Ignition, Reference Paragraph AC 29.863c(1) of AC 29-2B Stop Minimize the Hazard if Ignition does Occur, Reference Paragraph AC
29.863c(2) of AC 29-2B Stop, FAR Section
29.863 Satisfied FIGURE AC 29.863-1 Page D - 128
SUBPART D - DESIGN AND CONSTRUCTION EXTERNAL LOADS.
AC 29.865. § 29.865 (Amendment 29-12) EXTERNAL LOAD ATTACHING MEANS.
a. Background. The external load atta ching means standards for transport and normal category rotorcraft were originally contained in Subpart D, “Airworthiness Requirements of FAR Part 133, Rotorcraft External-Load Operations.”
Amendment 29-12, in 1977, added a new § 29.865, which moved these standards from Part 133 to Part 29. An identical transfer occurred in 1977 for Part 27. Transport Category A and B rotorcraft were initially used under Part 133 operations and, after Amendment 133-6, restricted category rotorcraft were also included under Part 133 operations. The use of restricted category first came about when an operator, exempt from Part 133, transferred harbor pilots to and from ships by a hoist and sling. The exemption was granted to study the feasibility of passenger transfer outside of the cabin. Subsequently, Amendment 133-9, adopted in January 1987, established a new Class D rotorcraft load combination for transporting passengers external to the rotorcraft. Amendment 133-9 also provided for the limitations and conditions for external passenger transportation and the necessary, associated safety requirements.
Part 29 rules have not yet been changed to reflect the Class D requirements.
b. Explanation. While the regulati on only addresses external load attaching means, this advisory material also includes guidance for certification of external load carrying devices for rotorcraft to be used in conjunction with Part 133, “Rotorcraft External Load Operations.” Subpart D of Part 133 contains supplemental airworthiness requirements. Part 1 defines four classe s of rotorcraft load combinations which are operationally approvable under the Part 133 operating rules and, thus, are eligible for certification under § 29.865. Parts 1 and 133 (through Amendment 133-9) contain a new rotorcraft load combination, Class D, that addresses personnel carried externally.
The four classes of rotorcraft load combinations are summarized in FIGURE AC 29.865-1 and are discussed in detail in paragraph c. For further information, AC 133-1A, “Rotorcraft External-Load Operations in Accordance with Federal Aviation Regulations Part 133,” October 16, 1979, may be reviewed. Also, paragraph AC 29.25 (reference § 29.25) concerns, in part, jettisonable external cargo.
c. Procedures.
(1) The applicant should clearly identify the Parts 1 and 133 rotorcraft load combination classes (A, B, C, or D) that are being applied for. The loads and operating envelopes for each class 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 (for Class D operations) the personnel carrying device meets the requirements of §§ 29.865(a),
133.41, 133.43, and 133.45(e)(3) for the proposed operating envelope.
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(2) For rotorcraft load combination classes A, B, and C, § 29.865 requires use of 2.5 g vertical limit load factor (NZW) at the maximum substantiable cargo load (which is typical for cargo hauling configurations). This 2.5 g limit load factor is based on an engineering evaluation and a rationalization of § 29.337 for high gross weight applications. However, for lower gross weight configurations (which are more typical of a Class D application; i.e., personnel transport or evacuation), a higher limit load factor is recommended to ensure that limit load is never exceeded in service. For example, a Class D external load carrying device which is certified to a limit vertical load factor of
2.5 g and is installed in a minimum gross weight configuration rotorcraft capable of generating a vertical limit load factor of 3.2 g’s could experience ((3.2/2.5 X 1.5) X 100) - 85 percent of ultimate load under emergency conditions with new external hardware. However, if fact ors such as wear and corrosion have effected the structural integrity of the external hardware ultimate load could be exceeded in emergency service. In any case, FAA/AUTHORIT Y policy is to not exceed limit load in service. The higher load factor for Cla ss D cases should be the analytically derived maximum vertical limit load factor for the restricted operating envelope being applied for; or, as a conservative option, a vertical limit load factor of 3.5 g’s (reference § 29.337). Unless a more rational proposal is received, for Class D cases where maximum operating gross weight for external load is between design maximum weight and design minimum weight, linear interpolation can be used between NZW MIN and NZW MAX versus gross weight for design limit load factor determination.
(3) For applications that employ winches (or hoists) to raise or lower an external load from a hover (or another phase of flight), limit load must be properly determined based on the characteristics of the winch system and its installation such as mechanical advantage, static strength of the winch, static strength of its installation and the payload for any operating scenario being applied for. One acceptable method of determining limit load is by the following procedure:
(i) Determine the basic loads that fail and unspool the winch or its installation, respectively (Note: This det ermination should be based primarily on static strength; however, any dynamic load magnification factors that are significant should be accounted for).
(ii) Select the lower of the two values from (i) as the ultimate load of the winch system installation.
(iii) Divide the selected ultimate load by 1.5 to determine the limit load of the system.
(iv) Compare the system’s derived limit load to the applied for one “g” payload multiplied by the maximum downward vertical load factor (NZW MAX) from paragraph (2) to determine the critical payload’s limit value.
(v) If the critical limit payload is equal to or less than the system’s derived limit load the installation is structurally approvable as presented.
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(vi) If the critical limit payload exceeds the system’s derived limit load then one of the following options should be considered:
(A) Disapproval.
(B) Application for exemption.
(C) Reduction of the applied for critical limit payload to less than or equal to the system’s derived limit load.
(D) Redesign of the winch system (and installation) to increase its derived limit load to equal to or greater than the critical payload.
(E) A combination of options (C) and (D).
(F) Approvable operating restrictions to reduce NZW MAX and, the corresponding critical limit payload to less than or equal to the system’s derived limit load.
(4) In all approved cases, appropriate winch system placards and flight manual restrictions should be provided. Also, for Class D load combinations, the winch or hoist should have a demonstrated, acceptable level of reliability (for the phases of flight in which it is operable and in which the Class D load is carried externally). The winch should be disabled (or utilize an overriding mechanical safety device such as a flagged removable shear pin) to prevent inadvertent load unspooling or release during the phases of flight that the load is carried externally and operation is not intended. The maximum allowable winch cable angle should be determined and approved. This is primarily a structural requirement but should also be reviewed from an interference and flight handling criteria standpoint.
(5) It is recommended that winch or hoist systems be demonstrated as follows:
(i) At least 1/3 of the demonstration cycles should include the maximum aft angular displacement of the load from the drum applied for under § 29.865(a).
(ii) The load versus speed combinations of the winch should be demonstrated by showing repeatability of the no load-speed combination, the 50 percent load-speed combination, the 75 percent load-speed combination and the system limit load-speed combination.
(iii) A minimum of six consecutive, complete operation cycles should be conducted at the system’s critical limit load speed combination.
(iv) In addition, the demonstration should cover all normal and emergency modes of intended operation and should include operation of all control devices, limit switches braking devices, and overload sensors in the system.
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(v) Quick disconnect devices, and cable cutters should be demonstrated at 25 percent, 50 percent, 75 percent, and 100 percent of system limit load. Any electrical load release devices for Class D loads should be treated as a novel design feature and should be coordinated with the Rotorcraft Directorate.
(vi) Any devices or methods used to increase the mechanical advantage of the winch should also be demonstrated.
(vii) During each demonstration cycle, the winch should be operated from each station from which it can be controlled.
(viii) Operating manuals, flight manuals, and associated placards should be used and proofed during the demonstration.
(6) For all applications, it is good practice to obtain the gross weight range limits, the corresponding limit load factors (NZW), and substantiate the system, accordingly, for the critical loads. This procedure determines the critical basic loads and associated operating envelope for the rotorcraft load combination categories requested.
(7) For a request involving more than one class of rotorcraft load combinations, structural substantiation is required only for the critical case if accurately determinable from analysis.
(8) Appropriate placards, markings, and flight manual restrictions should be provided as determined by load capacities and operational restrictions. Each placard, marking, and flight manual supplement should be checked during TIA flight testing.
(9) For load Classes A, B, C, and D, the basic vertical limit load factor (NZW) from (c)(2) is converted to ultimate by multiplying the maximum applied load (i.e., the sum of the carrying device load and cargo or personnel loads) by 1.5 (for restricted category approvals, see guidance in paragraph AC 29 MG 5.) This load is used to substantiate all existing structure affected and all added structure associated with the external load carrying device and its attachments. Casting and/or fitting factors are to be applied where appropriate. For load Class D, the weight of each occupant carried externally should be assumed, for analysis purposes, to be that of the 95 percentile (202 pound) man (reference MIL-STD-1472, “Human Engineering Design Criteria for Military Systems, Equipment and Facilities).
(10) For load Classes B, C, and D, the maximum limit external load for which certification is requested, even though it may otherwise be much less than the maximum system capacity; e.g., cargo hook capacity, etc., should not exceed the rated capacity of the quick release device used in the applicant’s proposed design or, for Class D only, the rated capacity of the personnel carrying device. The quick release and personnel carrying devices should be strength tested (with FAA/AUTHORITY witness) or otherwise structurally substantiated to determine their allowable limit load capacity, if it has not been previously approved or was not produced to a recognized and approvable industry or military standard.
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(11) For load Classes B, C, and D, in substantiating analyses and tests, the maximum ultimate external load is specified to be applied at the sling-load-line to rotorcraft vertical axis (Z axis) angles up to 30°, except for the forward direction. The 30° angle may be reduced, if impossible to obtain due to physical constraints, or operating limitations. If the angle is reduced, appropriate placards and flight manual changes are required.
(12) For load Classes B and C, an external releasing system is mandated which requires an approved primary quick release device to be installed on one of the pilot’s primary controls. The quick release device (typically installed on the cyclic stick) is designed and located to allow the pilot to accomplish load release without hazardously limiting his ability to control the rotorcraft during emergency situations. A manual (backup) mechanical quick release device is also required. This control must also be readily accessible to the pilot or another designated crew member, such as a hoist operator. For Class B and C cargo applications, a sufficient amount of slack should be provided in the control cable to permit cargo hook movement without tripping the hook release.
(13) For Load Class D, an emergency release system is specified by § 133.45(e)(4) which requires two distinct actions for load release. This is intended for the phases of flight that the load is carried (and/or retrieved) externally. This release can be operated by the pilot from a primary control or, after a command is given by the pilot, by a dedicated crewmember from a remote location. Two distinct actions are required for the primary release to provide a higher level of safety for Class D human external loads. If the manual backup device is a cable cutter, it should be properly secured but readily accessible to the dedicated crewmember intended to use them.
(14) For Class D (human) load applications, to ensure personnel safety, the emergency release system design and associated placarding should be given special consideration. As stated previously, electrical release designs should be reviewed by the Rotorcraft Directorate prior to approval.
(15) For the majority of Class D applications, an approved single or multiple personnel carrier or container is required. The carrier or container may be previously approved or may be approved as part of the certification process. In any case, the single or multiple personnel carrier or container should be substantiated for the allowable ultimate load as determined under paragraphs c(2), (3), (4), (5), (6), (7), (8), and (9) above. The personnel carrier or container should be placarded for this capacity and show the proper internal arrangement and/or location of the intended occupants.
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Some exceptions may exist that are certifiable under Class D that involve the technique of “Rappelling” from a rotorcraft. Rotorcraft lo ad-combination D allows for such applications by definition (reference § 1.1). Other types of human cargo devices can be applied for under the Class D external load combination definition. An example is external carriage of personnel in a conveyance rigidly attached to the rotorcraft (e.g., cage, pod, secured litter or strap harness/seat arrangement).
(16) The personnel carrier or container should be easily and readily ingressed or egressed. Appropriate placards are required to provide ingress and egr ess instructions. For door latch fail -safety, more than two fastener or closure devices are recommended. Direct visual inspectability of the latch device by both crew and passengers is recommended to ensure it is fastened and secured. Any fabric, if used, should be durable and should meet the flammability standards of safety belts as stated in TSO C-22. Sharp corners and edges should be avoided, and padding should be used when necessary to protect the carrier and container occupants.
(17) The U.S. Coast Guard has three containers or devices that are used with rotorcraft for emergency rescue work. These devices and their National Stock Numbers are listed below. These devices have not been FAA/AUTHORITY approved; however, applications which involve them may be submitted for approval.
National Stock No. Title 6530-00-042-6131 Stokes litter (one person) 1670-00-HR0-7970 Rescue basket 1680-090-511-2712 Rescue sling (one person) NOTE: The rescue sling is a “collar” device that requires a person to exert some effort to remain in the collar. This sling should only be used in conjunction with properly written instructions and with personnel trained in the proper use of the sling.
(18) Flight test verification work that thoroughly checks out the operational envelope should be accomplished with every device approved for external cargo carriage (especially rotorcraft load combination D which includes external human cargo). The flight test program should show that all aspects of the applied for operations are safe, uncomplicated and can be conducted by an average flight crew under the most critical service environment and, in the case of human external cargo, under the pressures of an emergency scenario.
AC 29.865A. § 29.865 (Amendment 29-30) EXTERNAL LOAD ATTACHING MEANS.
a. Explanation. Amendment 29- 30 added two requirements to § 29.865:
(1) Section 29.865(a) is clarified to allow use of a design factor less than 2.5g’s, for rotorcraft load combinations A, B, and C non-human external cargo applications provided the lower load factor is not likely to be exceeded by virtue of the Page D - 134
rotorcraft characteristics and capability. That is the rotorcraft design factors may be used for the cargo device system.
(2) Section 29.865(d) was added to clarify and specify the fatigue requirements for the external cargo attaching means. The “rotorcraft” standard is contained in § 29.571, paragraph AC 29.571.
b. Procedures.
(1) For § 29.865(a), if a design limit load factor less than 2.5g’s is requested, the applicant should provide a rational analysis and/or a flight operations data base that clearly shows that the load factor requested is unlikely to be exceeded in service.
Note: § 29.337(b) requires use of 2.0 g’s as a minimum.
(2) For § 29.865(d), all failures of the cargo attaching means (and the associated critical components) that are likely to be hazardous to the rotorcraft should be identified by an acceptable means such as an FMEA. The critical components associated with these failure modes should then be analyzed and/or tested to ensure that the likelihood of a fatigue failure or occurrence is acceptably minimized. In the majority of cases an analysis using the methods of AC 27 MG-11, “Fatigue Evaluation of Rotorcraft Structure”, will be sufficient. Any component’s airworthiness limitations and/or mandatory inspections should be identified by this analysis, approved, and placed in the airworthiness limitations section of the maintenance manual or Instructions for Continued Airworthiness. See paragraph AC 29.1529 (§ 29.1529) for information on these manuals.
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AC 29-2C, Chg 1 2/12/03 FIGURE AC 29.865-1 SUMMARY OF PART 133 ROTORCRAFT LOAD COMBINATIONS CERTIFIABLE UNDER § 29.865
CLASS A Basic Definition and Intended Use Fixed External Cargo Container Is defined by § 1.1 as a load combination in which the external load cannot move freely, cannot be jettisoned, and does not extend below the landing gear. This category usually features multiple attachments (loadpaths) to the airframe. Typical example is a hard mounted cargo basket attached to the rotorcraft crosstubes which is used to carry cargo from point A to point B.
Typical Load Limits Certification limit is NZW X Maximum Substantiable External load. N ZW is 2.5 per § 29.865 (See Procedure, paragraph (2)).
Quick Release Requirements None. Cargo and its container are not jettisonable.
Certification Requirements -- Considerations
- For cargo only.
- Flight Manual Restrictions - § 133.47 requires a rotorcraft load combination flight manual supplement. Any flight envelope restrictions from § 29.865 should be a part of this supplement.
- Load limit placards are required by § 29.865(c).
- Flight envelope restriction placards may also be required for gross weight limitations, e.g., limitations, elimination of dangerous maneuvers, etc.
- Cargo tiedowns to prevent load shifting relative to airframe may be required.
- Effect of external cargo carrier and its maximum cargo weight on load paths, loads and fatigue of existing structure should be determined.
- TIA testing may be necessary to determine whether or not the system performs as intended and if placards and flight manual supplements are adequate.
- The applicant may elect to test the aerodynamic effect of several representative load shapes and include applicable information in the flight manual supplement. If such information is not in the RFM, then the operator may be required to obtain an operations approval under Part 133.
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