an analysis. Compliance with § 29.1193(e)(3), fireproof skins will involve airframe and propulsion disciplines for rotorcraft designs that do not have cowls.
361A. § 29.861 (Amendment 29-30) FIRE PROTECTION OF STRUCTURE.
CONTROLS, AND OTHER PARTS.
a. Explanation.
(1) Amendment 29-30 revised the standard for Category B rotorcraft to allow use of parts made from standard fireproof materials of known acceptable dimensions in areas affected by powerplant fires without further proof of qualification. Previously the standard imposed a performance criterion for Category B applications regardless of the materials and part dimensions used.
(2) Fireproof and fire resistant are defined in FAR Part 1, § 1.1.
b. Procedures.
(1) A part with acceptable geometry that is made of steel, or another fireproof material, may be used to comply with the standard.
(2) A material system, panel, or assembly would be equivalent to steel provided it successfully completes the flammability tests described in Paragraph 361b4(vi) of this AC for the appropriate time period that includes fire recognition.
362. § 29.863 (Amendment 29-17) FLAMMABLE FLUID FIRE PROTECTION.
a. Background.
(1) The development of current § 29.863 can be traced through CAR 7.483, § 29.863 (1968), NPRM 68-18 (1968), and NPRM 75-26 (Airworthiness Review Notice November 7, 1975) and subsequent Amendment 29-17.
(2) Investigation of two accidents disclosed evidence of in-flight fires caused by leakage of flammable fluids to ignition sources. The revisions to § 29.863 adopted by Amendment 29-17 require significantly more attention to overall fire protection and prevention.
b. Explanation.
(1) Prior to Amendment 29-17, this rule only required either a means to prevent ignition of flammable fluids or vapors or a means to control any resulting fire. Isolation of flammable fluids and vapors from ignition sources by shrouding or sealing was the normal method of compliance. The revised rule further requires the assumption that 538 Par 361
these means fail or are ineffective and a fire does actually occur. Means to minimize the consequence of these fires must be provided. Specifically identified considerations must include the flammability of any combustible or absorbing materials, electrical faults, malfunction of protective devices, etc.
(2) The rule does not go so far as to require the entire rotorcraft to be a "designated fire zone."
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:
(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.).
(ii) Provide other effective separation, ventilation, or overheat shutdown devices, etc., to preclude ignition.
(iii) Assure that electrical equipment in the areas subject to flammable fluids and vapors is either hermetically sealed or has been tested and shown to be free of ignition capability. Paragraph 621b(1) (iv) of this advisory circular describes an acceptable standard for such laboratory testing.
(iv) Place a restricting orifice in fluid pressure lines routed to instruments and transducers.
(v) Assure fluid lines are not located so as to be subject to abrasion during normal operations. Cargo compartments should be evaluated for potential line damage due to cargo movement.
(2) To minimize the hazards if ignition occurs:
(i) Provide fireproof designs, fire wall isolation, or equivalent means for critical structure, equipment and personnel areas.
Consider fire detection, extinguishment, shutoff valves, fire suppression systems, etc.
(3) In considering compliance the actual protective measures may be related to the situation, considering the quantity and flammability characteristics of the fluid, the fire damage tolerance of the area, and the means available to the crew to minimize hazards from the fire. If action by the crew is necessary, quick-acting means (not necessarily fire detectors) must be provided to alert the crew in the event of a fire.
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Details of any action required by the crew should be included in the Rotorcraft Flight Manual.
(4) Compliance with § 29.863(d) requires as a minimum, type design data defining each area where flammable fluids or vapors might escape.
363.-372. RESERVED.
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SECTION 22. EXTERNAL LOAD ATTACHING MEANS.
373. § 29.865 (Amendment 29-12) EXTERNAL LOAD ATTACHING MEANS.
a. Background. The external load attaching 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 regulation 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 Operationsi Subpart D of Part 133 contains supplemental airworthiness requirements. Part 1 defines four classes 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 Table 373-1 and are discussed in detail in Paragraph c. For further information, AC 133-1A, "Rotorcraft External-Load Operations in Accordance with FAR Part 133," October 16, 1979, may be reviewed. Also, Paragraph 43 of this AC (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 factors 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/AUTHORITY policy is to not exceed limit load in service. The higher load factor for Class 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 Nw 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 determination 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.
(ili) 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.
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(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.
(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.
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:
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.
(ill) A minimum of six consecutive, complete operation cycles should be conducted at the system's critical limit load speed combination.
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(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.
(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.
(vili) 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 (l.e., the sum of the carrying device load and cargo or personnel loads) by 1.5 (For restricted category approvals, see guidance in Paragraph 785.) 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).
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(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.
(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 satety, 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 Par 373 555
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.
Some exceptions may exist that are certifiable under Class D that involve the technique of "Rappelling" from a rotorcraft. Rotorcraft load-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 egress 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.
373A. § 29.865 (Amendment 29-30) EXTERNAL LOAD ATTACHING MEANS.
a. Explanation. Amendment 29-30 added two requirements to § 29.865:
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(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 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 230, of this AC.
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 20-95, "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 729 (§ 29.1529) of the AC for information on these manuals.
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TABLE 373-1 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. Nzw 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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TABLE 373-1 (continued) SUMMARY OF PART 133 ROTORCRAFT LOAD COMBINATIONS CERTIFIABLE UNDER § 29.865
CLASS B Basic Definition and Intended Use Single Point Suspension External Load Airborne Is defined by § 1.1 as a load combination in which the external load is jettisonable and is lifted free of land or water during the rotorcraft operation. The payload is typically suspended from a hook or a similar device. The hook may be attached to the rotorcraft structure or it may be attached to a movable hoist cable and the hoist itself attached to the rotorcraft. Typical use is to lift a cargo load until it is completely airborne and fly it from point A to point B. The load on the hoist may be stowed in the fuselage (in some cases) while being transported.
Typical Load Limits Certification limit load is Nzw × Maximum Substantiable External load. Nzw is 2.5 per § 29.865 (See Procedure, Paragraph (2)). Load may be limited by hoist allowables (reference Paragraph (3)).
Quick Release Requirements § 29.865(b)(1) requires that a primary quick release system control device be installed on a primary control. Also, a manual quick release system backup actuation device must be available and readily accessible.
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.
- Certifiable external cargo load capacity may be further limited by §§ 133.41 and 133.43
- Quick release devices must be approved and be operable on a nonhazard basis by the pilot per § 29.865(b).
- Manual backup must be reliable but need not be overly sophisticated (cable cutters, axes, etc., used by crew members)
- Effect of maximum suspended load and its attachment to rotorcraft structure 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.
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