Page D - 83 AC 29.785. § 29.785 SEATS, SAFETY BELTS, AND HARNESSES .
a. Explanation .
(1) This section requires that seats, belts, harnesses, and adjacent parts of the rotorcraft be substantiated for the structural loads resulting from the inertia forces of § 29.561 as well as normal flight and ground inertia forces on a 170-pound occupant.
The inertia forces of § 29.561 are ultimate loads and must be multiplied by a factor of
1.33 in determining the “strength of attachment” of each seat to structure and each belt or harness to structure. The seat, belt, etc., are required to sustain applied loads and to protect the occupant from serious injury. The pilot seats must also sustain the effects of the pilot forces of § 29.397.
(2) In addition, the “occupant must be pr otected from head injury” by the seat belt and one of the following:
(i) A harness to prevent the head from contacting an injurious object.
(ii) Elimination of injurious obj ect within striking distance of the head.
(iii) A cushioned rest as specified.
(3) Handholds are required to steady occupants using the aisle in moderately rough air.
(4) Projecting objects which would inju re occupants “in normal flight must be padded.”
b. Procedures .
(1) Each seat with its belts and harnesse s are to be substantiated for the flight, ground, and emergency landing loads of § 29.561 by structural test or stress analysis.
Section 29.785(b) states that “each seat must be approved.” Certification approval can be gained by Technical Standard Order (TSO) approval or by accomplishing sufficient structural substantiation to gain FAA/AUTHORITY approval of the seat and its belt(s) as part of the Type Design of the rotorcraft. TSO No. C-39 concerns standards for aircraft seats, including rotorcraft seats. If TSO No. C-39 is used as an approval basis for a specific rotorcraft seat, the seat should be checked to assure it has been substantiated for the vertical (up and down) and side loads imposed by installation in the aircraft. For example, TSO No. C-39 (and NAS 809) specifies an ultimate down load of 4.0g which is in agreement with the 4.0g emergency landing load factor of § 29.561, but it may be less than the design maneuver load factor (which can be as high as 3.5g limit or 5.25g ultimate).
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(i) The 1.33 factor is specified fo r substantiation of attachments of each seat to the structure and each safety belt or harness to the seat or structure for § 29.561 loads, whether analysis or test is used.
(ii) If static testing of seats, belts, and harnesses is used, the body block of NAS 809 may be used. The corners of the NAS 809 body block may be radiused and padded if it is found that the small radii cause premature, unrealistic crippling of thin wall tubing or other structure used in the seat.
(iii) The substantiation of the pilot seats is required to include pilot forces of § 29.397 in conjunction with normal flight and ground loads. For example, the pilot foot force (195 pounds ultimate) must be reacted by the seat.
(2) The following criteria have been f ound satisfactory for preventing occupant head injuries:
(i) If a harness is used, it shoul d support the shoulders without applying hazardous loads to the side or front of the neck. It should be easily donned and a single point release with the seat belt is preferred. If separate release is provided, it must be simple, compatible with the seat belt release, and near the seat belt release. The harness should be tested in conjunction with the seat belt using a “body block” similar to that of NAS 809 if possible. If the harness is tested separately from the belt, it should be tested to 50 percent of the forward crash loads for the entire occupant weight of 170 pounds, unless that percentage distribution is found to be unrealistic by a rational analysis.
(ii) Elimination of injurious objec ts within striking distance of the head and other vital parts can be accomplished by removal of objects with sharp edges or rigid surfaces from within striking distance of vital parts of the occupant. Dimensions and weights for typical occupants are available in U.S. Army USAAULABS Reports 70-22 (August 1969) and 66-39 (June 1966) and NACA Report TN 2991 (August 1953).
Because of the range of occupant head striking distance, a combination of “elimination of injurious objects” and “cushioned rests” may be required for some interior configurations.
(iii) An acceptable cushioned rest can be provided by use of a 1-inch thickness of foamed polyvinyl chloride (PVC), or equivalent energy absorbing material.
The density of material should be in the 5 to 10 pounds per cubic foot density range.
PVC foam has the property of absorbing energy efficiently with negligible rebond effects. PVC foam recovers slowly to the original configuration after deformation. If PVC foam is used, however, care must be taken in its application relative to its flammability characteristics (reference § 29.853).
(3) Handholds for the occupants are gener ally provided by seat backs adjacent to the aisle. If the seat backs fold, the amount of support provided by the seat backs before they fold must be evaluated in a furnished interior or mock up. To provide
Page D - 85 adequate support, the seat back may use an easily disengaged latch or adequate friction in the hinge mechanism to obtain adequate support. Handholds along the aisle are, of course, not needed for rotorcraft with no aisles or where seat belts must be fastened during flight.
(4) Projecting objects which could in jure occupants in normal flight should be padded. The amount of padding required depends on the location, size, and minimum radius of the projecting object. In general, this requirement will mean that sharp edges must be padded with one-half inch of PVC foam or equivalent (5 to 10 lbs. density), while objects with radii in excess of 1 inch may meet the requirements of § 29.785(e) with a lesser amount of energy absorbing padding, if it can be contacted only by persons “moving about in the rotorcraft in normal flight.”
AC 29.785A. § 29.785 (Amendment 29- 29) SEATS, BERTHS, BELTS, SAFETY BELTS, AND HARNESSES.
a. Explanation . Amendment 29-29 makes the following changes to § 29.785:
(1) The title of § 29.785 now includes berths (which would include litters).
(2) Section 29.785(a) has been revis ed to include reference to the new § 29.562, “Emergency Landing Dynamic Conditions.”
(3) Section 29.785(b) has been revised to include a reference to the new § 29.562(c)(5) head injury criteria and to describe a torso restraint system that is contained in TSO-C114.
(4) Section 29.785(f) has been revi sed to change the percentage of load distribution for safety belt and harness combination to 60-40.
(5) A new § 29.785(i) has been added whic h provides a list of “seating device system” components.
(6) A new § 29.785(j) provides for deformations of the seat energy absorption device system installed to meet the requirements of § 29.562 but requires that the system “remain intact and not interfere with rapid evacuation of the rotorcraft.” Further “structural” performance standards are contained in §§ 29.562(c)(1) and (2).
(7) A new § 29.785(k) provides static strength and restraint requirements for litters and berths. Litters may be oriented laterally as well as longitudinally in the rotorcraft. Dynamic tests of litters are not required. For longitudinally oriented litters, features should be provided to protect the occupant from the increased loads in § 29.561(b) of Amendment 29-29.
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b. Procedures . The procedures of paragraph AC 29.785 still apply to static substantiation of the seats, berths, safety belts, and harness. In addition:
(1) Compliance with § 29.562 (except li tters are not included) and § 29.561(b) is required.
(2) Section 29.562 includes a specific pass fail criteria, which includes head injury criteria.
(3) Shoulder harnesses need only be subs tantiated for 40 percent of total occupant load rather than the former 60 percent adopted by Amendment 29-24.
(4) AC 29.562 provides guidance for ev aluating the functioning of a seating energy absorption device system under dynamic test conditions. Stroking is associated with the vertical-horizontal impact case and is recognized in the static strength substantiation.
(5) Berths or litters installed within 15° or less of the rotorcraft longitudinal axis (oriented longitudinally) shall use a combination of restraint devices, such as are required to be equipped with a padded end-board, cloth diaphragm, or equivalent means to withstand and distribute the occupant loads resulting from § 29.561(b) requirements. Other berths or litters may be equipped with straps or safety belts to withstand the forward reaction of § 29.561(b) as well as other loads, including flight loads.
(i) Berths/litters may be substantiat ed by static load tests, analysis, or a combination thereof and need not be substantiated to the 1.33 fitting factor of seat installations.
(ii) The berth/litter occupant’s head, neck, and spine should be protected from (landing) impact forward loads by appropriate design means; e.g.,
• non-longitudinal orientation of the berth/litter; or
• “feet forward” orientation; or
• distribution of an appropriate per centage of forward loads on the shoulders (not solely to the head and spine).
(iii) Recommendations for litter occupants:
• If the occupant’s head is oriented forward, a shoulder harness should be provided, in conjunction with body and leg straps that prevents the occupant’s head from falling off the litter. A padded end board, diaphragm, etc., may be used, provided head and spinal loads are alleviated or prevented.
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• If the occupant’s feet are or iented forward, the padded end board may also be used in combination with the body and leg straps or other such restraints.
• Multiple or combinations of devices should be used to distribute the occupant loads as well as protect the occupant from possible neck and spine compression.
AC 29.785B § 29.785 (Amendment 29-42) SEATS, BERTHS, LITTERS, SAFETY BELTS, AND HARNESSES.
a. Explanation. Amendment 29-42 revised the title of the rule to now include litters to distinguish from berths. Additionally, § 29.785(k) was revised to require that the 1.33 fitting factor of § 29.625(d) must be applied to the emergency landing loads of § 29.561(b)(3) for the substantiation of attachments of each berth and litter to the structure.
b. Procedures. All of the advisory material pertaining to this section remains in effect with the following additions:
(1) A fitting factor of 1.33 must be applied to the emergency landing loads of § 29.561(b) when evaluating the berth or litter attachment and the occupant restraint system to the structure.
(2) The 1.33 factor is required whether analysis or test is used.
AC 29.787. § 29.787 (Amendment 29-12) CARGO AND BAGGAGE COMPARTMENTS.
a. Explanation .
(1) This section requires that cargo and baggage compartments be designed for normal flight and ground loads and for a 4g ultimate forward load condition.
Maximum placarded weights and critical distributions are to be considered.
(2) Means to prevent cargo shifting and contact between any cargo lamp bulb and cargo is to be provided.
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b. Procedures . Structure tests or analyses may be used for substantiation for the design loads.
(1) Nets or straps may be used to prev ent cargo shifting. The nets or straps are required to be substantiated for the structural loads. They need a means for adjustment to assure proper restraint for different sizes and shapes of cargo.
(2) Cargo lamp bulbs need to be guarded, recessed, or placed in upper inside corners to prevent contact with cargo.
AC 29.787A. § 29.787 (Amendment 29-31) CARGO AND BAGGAGE COMPARTMENTS .
a. Explanation . Amendment 29-31 adds two subparagraphs to § 29.787 (c) which clarify that cargo and baggage compartments should be designed to protect occupants from injury by the compartment contents during emergency landings. This may be done by location or by retention provisions. The new paragraphs also add a requirement that the compartment contents should not cause injury when subjected to the loads of § 29.561.
b. Procedures . The procedures of paragraph AC 29.787 are still applicable. In addition to the forward load, the cargo and baggage compartments should be designed to withstand loads in other directions as specified in § 29.561. Also, the compartment may be shown to provide protection of occupants by location; i.e., cargo and baggage compartments may be shown to be located in a position where loose contents will not endanger occupants in an emergency landing. If the compartment is located above or behind the occupied area, § 29.561(c) still applies. If a compartment is in the occupied area, § 29.561(b) may apply.
AC 29.801. § 29.801 (Am endment 29-12) DITCHING.
a. Explanation .
(1) Ditching certification is acco mplished only if requested by the applicant.
(2) Ditching may be defined as an emergen cy landing on the water, deliberately executed, with the intent of abandoning the rotorcraft as soon as practical. The rotorcraft is assumed to be intact prior to water entry with all controls and essential systems, except engines, functioning properly.
(3) The regulation requires demonstrati on of the flotation and trim requirements under “reasonably probable water conditions.” The FAA/AUTHORITY has determined that a sea state 4 is representative of reasonably probable water conditions to be encountered. Therefore, demonstration of compliance with the ditching requirements for at least sea state 4 water conditions is considered to satisfy the reasonably probable requirement.
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(4) A sea state 4 is defined as a moder ate sea with significant wave heights of 4 to 8 feet with a height-to-length ratio of:
(i) 1:12.5 for Category A rotorcraft.
(ii) 1:10 for Category B rotorc raft with Category A engine isolation.
(iii) 1:8 for Category B rotorcraft.
The source of the sea state definition is the World Meteorological Organization (WMO) Table. (See figure AC 29.801-1.)
(5) Ditching certification encompasses four primary areas of concern: rotorcraft water entry, rotorcraft flotation and trim, occupant egress, and occupant survival.
(6) The rule requires that after di tching in reasonably probable water conditions, the flotation time and trim of the rotorcraft will allow the occupants to leave the rotorcraft and enter liferafts. This means that the rotorcraft should remain sufficiently upright and in adequate trim to permit safe and orderly evacuation of all personnel.
(7) For a rotorcraft to be certifi ed for ditching, emergency exits must be provided which will meet the requirements of § 29.807(d).
(8) The safety and ditching equipm ent requirements are addressed in §§ 29.1411, 29.1415, and 29.1561 and specified in the operating rules (Parts 91, 121, 127, and 135). As used in § 29.1415, the term ditching equipment would more properly be described as occupant water survival equipment. Ditching equipment is required for extended overwater operations (more than 50 nautical miles from the nearest shoreline and more than 50 nautical miles from an offshore heliport structure). However, ditching certification should be accomplished with the maximum required quantity of ditching equipment regardless of possible operational use.
(9) Current practices allow wide lati tude in the design of cabin interiors and consequently, the stowage provisions for safety and ditching equipment. Rotorcraft manufacturers may deliver aircraft with unfinished (green) interiors that are to be completed by the purchaser or modifier. These various “configurations” present problems for certifying the rotorcraft for ditching.
(i) In the past, “segmented” certification has been permitted to accommodate this practice. That is, the rotorcraft manufacturer shows compliance with the flotation time, trim, and emergency exit requirements while the purchaser or modifier shows compliance with the equipment provisions and egress requirements with the completed interior. This procedure requires close cooperation and coordination between the manufacturer, purchaser or modifier, and the FAA/AUTHORITY.
(ii) The rotorcraft manufacturer may el ect to establish a “token” interior for ditching certification. This interior may subsequently be modified by a supplemental
Page D - 90 type certificate or a field approval. Compliance with the ditching requirements should be reviewed after any interior configuration and limitations changes where applicable.
(iii) The Rotorcraft Flight Manual and supplements deserve special attention if a “segmented” certification procedure is pursued.
b. Procedures . The following guidance criteria has been derived from past FAA/AUTHORITY certification policy and experience. Demonstration of compliance to other criteria may produce acceptable results if adequately justified by rational analysis.
Model tests of the appropriate ditching configuration may be conducted to demonstrate satisfactory water entry and flotation and trim characteristics where satisfactory correlation between model testing and flight testing has been established. Model tests and other data from rotorcraft of similar configurations may be used to satisfy the ditching requirements where appropriate.
(1) Water entry .
(i) Tests should be conducted to establish procedures and techniques to be used for water entry. These tests should include determination of optimum pitch attitude and forward velocity for ditching in a calm sea as well as entry procedures for the highest sea state to be demonstrated (e.g., the recommended part of the wave on which to land). Procedures for all engines operating, one engine inoperative, and all engines inoperative conditions should be established. However, only the procedures for the most critical condition (usually all engines inoperative) need to be verified by water entry tests.
(ii) The ditching structural desi gn consideration should be based on water impact with a rotor lift of not more than two-thirds of the maximum design weight acting through the center of gravity under the following conditions:
(A) For entry into a calm sea--
( 1 ) The optimum pitch attitude as determined in 337(b)(1)(i) with consideration for pitch attitude variations that would reasonably be expected to occur in service;
( 2 ) Forward speeds from zero up to the speed defining the knee of the height-velocity (HV) diagram;
( 3 ) Vertical descent velocity of 5 feet per second; and
( 4 ) Yaw attitudes up to 15°.
(B) For entry into the maximum demonstrated sea state--
( 1 ) The optimum pitch attitude and ent ry procedure as established in
(b)(1)(i);
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( 2 ) The forward speed defined by the knee of the HV diagram reduced by the wind speed associated with each applicable sea state;
( 3 ) Vertical descent velocity of 5 feet per second; and
( 4 ) Yaw attitudes up to 15°.
(C) The float system attachment hardware should be shown to be structurally adequate to withstand water loads during water entry when both deflated and stowed and fully inflated (unless in-flight inflation is prohibited). Water entry conditions should correspond to those established in paragraphs AC 29.801(b)(1)(ii)(A) and (B). The appropriate vertical loads and drag loads determined from water entry conditions (or as limited by flight manual procedures) should be addressed. The effects of the vertical loads and the drag loads may be considered separately for the analysis.
(D) Probable damage due to water impact to the airframe/hull should be considered during the water entry evaluations; i.e., failure of windows, doors, skins, panels, etc.
(E) The ditching maximum demonstrated sea state for water entry is the same or greater than the maximum demonstrated sea state for flotation and trim.
(2) Flotation Systems .
(i) Normally inflated . Fixed flotation systems intended for emergency ditching use only and not for amphibian or limited amphibian duty should be evaluated for:
(A) Structural integrity when subjected to:
( 1 ) Air loads throughout the approved flight envelope with floats installed;
( 2 ) Water loads during water entry; and
( 3 ) Water loads after water entry at speeds likely to be experienced after water impact.
(B) Rotorcraft handling qualities throughout the approved flight envelope with floats installed.
(ii) Normally deflated . Emergency flotation systems which are normally stowed in a deflated condition and inflated either in flight or after water contact during an emergency ditching should be evaluated for:
(A) Inflation . The float activation means may be either fully automatic or manual with a means to verify primary actuation system integrity prior to each flight. If manually inflated, the float activation switch should be on one of the primary flight
Page D - 92 controls and should be safeguarded against spontaneous or inadvertent actuation for all flight conditions.
( 1 ) The inflation system design shoul d minimize the probability of the floats not inflating properly or inflating asymmetrically. This may be accomplished by use of a single inflation agent container or multiple container system interconnected together. Redundant inflation activation systems will also normally be required. If the primary actuation system is electrical, a mechanical backup actuation system will usually provide the necessary reliability. A secondary electrical actuation system may also be acceptable if adequate electrical system independence and reliability can be documented.
( 2 ) The inflation system should be safeguarded against spontaneous or inadvertent actuation for all flight conditions. It should be demonstrated that float inflation at any flight condition within the approved operating envelope will not result in a hazardous condition unless the safeguarding system is shown to be extremely reliable.
One safeguarding method that has been successfully used on previous certification programs is to provide a separate float system arming circuit which must be activated before inflation can be initiated.
( 3 ) The maximum airspeeds for intentional in-flight actuation of the float system and for flight with the floats inflated should be established as limitations in the RFM unless in-flight actuation is prohibited by the RFM.
( 4 ) The inflation time from actuation to neutral buoyancy should be short enough to prevent the rotorcraft from becoming more than partially submerged assuming actuation upon water contact.
( 5 ) A means should be provided for checking the pressure of the gas storage cylinders prior to takeoff. A table of acceptable gas cylinder pressure variation with ambient temperature and altitude (if applicable) should be provided.
( 6 ) A means should be provided to minimi ze the possibility of overinflation of the float bags under any reasonably probable actuation conditions.
( 7 ) The ability of the floats to inflat e without puncture when subjected to actual water pressures should be substantiated. A full-scale rotorcraft immersion demonstration in a calm body of water is one acceptable method of substantiation.
Other methods of substantiation may be acceptable depending upon the particular design of the flotation system.
(B) Structural Integrity . The flotation bags should be evaluated for loads resulting from:
( 1 ) Airloads during inflation and fully infl ated for the most critical flight conditions and water loads with fully inflated floats during water impact for the water entry conditions established under paragraph AC 29.801(b)(1)(ii) for rotorcraft desiring float deployment before water entry; or
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( 2 ) Water loads during inflation after water entry.
(C) Handling Qualities . Rotorcraft handling qualities should be verified to comply with the applicable regulations throughout the approved operating envelopes for:
( 1 ) The deflated and stowed condition;
( 2 ) The fully inflated condition; and
( 3 ) The in-flight inflation condition.
(3) Flotation and Trim . The flotation and trim characteristics should be investigated for a range of a sea states from zero to the maximum selected by the applicant and should be satisfactory in waves having height/length ratios of 1:12.5 for Category A rotorcraft, 1:10 for Category B rotorcraft with Category A engine isolation, and 1:8 for Category B rotorcraft. Model tests in a wave basin on a number of different rotorcraft types have indicated that an improvement in sea keeping, response of the rotorcraft to waves, performance of approximately one sea state can consistently be achieved by fitting float scoops. If the basic flotation system (without scoops) has demonstrated compliance with the minimum flotation and trim requirements, credit for float scoops to achieve stability in more severe water conditions may be allowed.
However, the effect of scoops on improved sea keeping must be demonstrated during model testing.
(i) Flotation and trim characteri stics should be demonstrated to be satisfactory to at least sea state 4 conditions.
(ii) Flotation tests should be invest igated at the most critical rotorcraft loading condition.
(iii) Flotation time and trim r equirements should be evaluated with a simulated, ruptured deflation of the most critical float compartment. Flotation characteristics should be satisfactory in this degraded mode to at least sea state 2 conditions.
(iv) A sea anchor or similar device should not be used when demonstrating compliance with the flotation and trim requirements but may be used to assist in the deployment of liferafts. If the basic flotation system has demonstrated compliance with the minimum flotation and trim requirements, credit for a sea anchor or similar device to achieve stability in more severe water conditions (sea state, etc.) may be allowed if the device can be automatically, remotely, or easily deployed by the minimum flightcrew.
(v) Probable rotorcraft door/window open or closed configurations and probable damage to the airframe/hull (i.e., failure of doors, windows, skin, etc.) should be considered when demonstrating compliance with the flotation and trim requirements.
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(4) Float System Reliability . Reliability should be considered in the basic design to assure approximately equal inflation of the floats to preclude excessive yaw, roll, or pitch in flight or in the water.
(i) Maintenance procedures s hould not degrade the flotation system
(e.g., introducing contaminants which could affect normal operation, etc.).
(ii) The flotation system desi gn should preclude inadvertent damage due to normal personnel traffic flow and excessive wear and tear. Protection covers should be evaluated for function and reliability.
(iii) Float design should provide a means to minimize the likelihood of damage or tear propagation between compartments. Single compartment float designs should be avoided.
(iv) Where practical, design of the flotation system should consider the likely effects of an uncontrolled water entry and locate system components away from the major effects of structural deformity.
(v) Visual identification of the he licopter following a ditching (and possible capsize) is made easier by the choice of material for the construction of the floats that has high visual conspicuity properties.
(5) Occupant Egress and Survival . The ability of the occupants to deploy liferafts, egress the rotorcraft, and board the liferafts should be evaluated. For configurations which are considered to have critical occupant egress capabilities due to liferaft locations and/or ditching emergency exit locations and floats proximity, an actual demonstration of egress may be required. When a demonstration is required, it may be conducted on a full-scale rotorcraft actually immersed in a calm body of water or using any other rig/ground test facility shown to be representative. The demonstration should show that floats do not impede a satisfactory evacuation. Service experience has shown that it is possible for occupants to have escaped from the cabin but have not been able to board a liferaft and have had difficulties finding handholds to stay afloat and together. Where practical, handholds or lifelines should be provided. The normal attitude of the rotorcraft and the possibility of a capsize should be considered when locating the handholds or lifelines.
(6) Rotorcraft Flight Manual . The Rotorcraft Flight Manual is an important element in the approval cycle of the rotorcraft for ditching. The material related to ditching may be presented in the form of a supplement or a revision to the basic manual. This material should include:
(i) The information pertinent to the limitations applicable to the ditching approval should include the range of sea state conditions that has been demonstrated for water entry and flotation stability. If the ditching approval is obtained in a segmented fashion (i.e., one applicant performing the aircraft equipment installation and operations portion and another designing and substantiating the liferaft/lifevest and ditching safety