69 seatbacks/accessories on these airplanes must be evaluated to ensure that an occupant would not suffer serious head injury from blunt trauma.
(iii) Currently, blunt trauma tests are conducted with seatback mounted accessories represented by actual production parts or parts that are similar in construction to the production parts. Industry has informed the FAA that certification delays occur due to the unavailability of actual accessories for testing. In addition, accessories are typically damaged during certification tests and are not usable in subsequent tests or for installation and delivery to a customer. Several specimens of the same part are repeatedly used, and damaged, during certification tests due to test failures or substantiating alternate seatback designs. This results in significant costs to manufacturers and customers.
(iv) The FAA has determined that it is acceptable to use a surrogate test article made of 6061-T4 aluminum which meets the criteria below in lieu of an accessory for demonstrating compliance with §§ 25.785(a) and (c) for blunt trauma assessments. An exception to the use of the surrogate test article occurs when the accessory is more rigid (deflects less and absorbs less energy during impact) than the plate defined in this AC. In that case, the accessory should be used in the test(s) and not a surrogate test article. The following criteria are applicable when using a surrogate test article during blunt trauma testing in accordance with §§ 25. 785(a) and (c):
(A) The surrogate part should be fabricated from 6061-T4 aluminum and have a minimum thickness of 0.238-inch (i.e., 0.25-inch minus a 0.012-inch manufacturing tolerance) at all locations. The length and width of the surrogate part should equal, within tolerances, the length and width of the actual part, respectively.
(B) The exposed surface of the surrogate part that will be impacted should be flat. That is, it is not required to have the contour of the accessory’s exposed surface represented by the surrogate part. Note that this is based on typical accessory installations which are essentially mounted flush with the seatback and have a generally homogeneous contact area.
Small variations in the surface due to the contour of plastic parts may be ignored. Designs that differ from this (e.g., a design with an exposed structural protrusion) might require the exposed surface of the actual part to be represented in order to adequately assess head injury potential.
(C) The weight of the surrogate part, and additional ballast if needed, should be ±10 percent of the weight of the actual part.
(D) The surrogate part should be located on the seatback in the same place
(i.e., within manufacturing tolerances for mounting the actual part) where the actual part would be located in terms of the x and y coordinates in Figure 83-1. The surrogate part should be located such that the surface, which will be contacted during the test, is at the same location (i.e., within manufacturing tolerances for mounting the actual part) where the actual part would be in terms of the z coordinate (refer to figure 83-1).
(E) The surrogate part should be attached to the seat by the final production hardware or a conservative representation of the final production hardware. For substantiating
70 blunt trauma requirements, a conservative representation of the attachment hardware would be at least as rigid as the actual hardware. The surrogate part should be mounted so that it would not move farther or faster, with respect to the seatback, than the actual part during the test.
(F) If the surrogate part cracks during a test, the test results are invalid.
(G) A surrogate part made of a material and thickness other than 6061-T4 aluminum in a nominal thickness of 0.25-inch may be used if an FAA Aircraft Certification Office finds that it is at least as rigid (i.e., it deflects less and absorbs less energy during the test).
Surrogate test articles which are less rigid than the aluminum surrogate part defined above are not addressed in this AC. If an applicant desires to use a surrogate part which is less rigid, its use should be approved through the issue paper process (or equivalent) or by an FAA policy memorandum. Testing may be required to determine the acceptability of these less rigid surrogate parts.
FIGURE 83-1 SURROGATE PART INSTALLED ON SEATBACK Surrogate part installed on the back side of the seatback in lieu of the actual accessory.
The x and y axes are in the plane of the backside of the seatback 71
(3) Paragraphs (a) and (c). The FAA issued policy memorandum ANM-03-115-31, dated May 9, 2005, and titled “Policy Statement on Conducting Component Level Tests to Demonstrate Compliance with §§ 25.785(b) and (d).” Appendix 13 of this AC contains the complete policy memorandum. Applicants may use the test methods in Appendix 13 to to demonstrate compliance with §§ 25.785(a) and (c) for both blunt force trauma and formation of post-impact sharp or injurious edges or features for items within the head strike zone as defined in figure 83-2. The policy is applicable to design certification projects whose certification basis includes Amendment 25-20, for §§ 25.785 (a) and (c). (Amendment 25-0)
(4) Paragraph (c). For sideward facing seats, this change removed the option of a safety belt, and eliminated the possibility of locating any injurious object within striking radius of the head. This option is still satisfactory for forward and aft facing seats. The "human cushion" or unpadded bulkhead concept is not an adequate energy absorbing rest and therefore does not comply with this amendment of the regulation. The shoulder harness may be a diagonal shoulder harness over the forward shoulder. (Amendment 25-15)
(5) Paragraph (c). The 18-degree requirement applies to both forward and aft facing seat installations. If the forward direction is considered as 0 degrees or 360 degrees of a circle, the segments from 18 degrees to 162 degrees and 198 degrees to 342 degrees are considered a side facing seat and the seat installation must comply with one of the two options stated in the regulation. (Amendment 25-20)
(6) Paragraph (c)(2). The striking radius of the head for a forward facing seat (head strike zone) is considered to be a zone whose length is bounded between an arc at the shoulder height of the 5th percentile female occupant (20.5-inches) and an arc at the limit of the head path (35-inches) whose centers are at the intersection of the plane of the uncompressed top of the seat bottom cushion with the plane of the uncompressed front of the back cushion; commonly referred to as the cushion reference point (CRP), as shown in figure 83-2. Previously this was referred to as seat reference point (SRP). However, with the advent of dynamic seat testing the definition for SRP was changed (refer to SAE ARP6626D). The head strike zone extends in the direction parallel to the airplane longitudinal axis. The width of the head strike zone is bounded by a vertical plane through the intersection of the centerlines of each armrest and the CRP as shown in figure 83-2. Typical installations to be considered are bulkheads, cabinets, tables, and passenger evacuation slide covers. The installation should not contain any pointed corners or sharp edges. The testing used to demonstrate that the installation is not injurious must take into account whether the system (e.g., seatback mounted telephone) is allowed to be used during taxi, takeoff and landing. If the system is allowed to be used during these phases of operation, the testing must consider the system in both the deployed and stowed position (e.g., seatback mounted telephone in or out of the cradle). If a surface or interior feature is located such that it is potentially hazardous in a combination of forward and side loads, it should be substantiated even if it might be slightly outside of the head strike zone. Any surface less than 18-inches above the floor need not be considered. Surfaces within the head strike zone may be padded with energy absorbing material, such as one inch of either Ensolite (Type AH, AHC, IV3, HHC or HH), Klegecell, or Airex 4070. Foam rubber is not satisfactory since it is an energy storing material. If the padding is easily removed, there should be acceptable placarding requiring the padding be in place during taxi, takeoff, and landing. (Amendment 25-0)
FIGURE 83-2 HEAD STRIKE ZONE FOR § 25.785 Head Strike Zone
20.5 inch 35 inch arc arc CRP 18 inches CRP Centerline 35 inch arc of Armrest Seat Axis Airplane Longitudinal Axis Centerline of Armrest Seat Axis ‚CRP Airplane Centerline Longitudinal Axis of Armrest 35 inch arc Centerline of Armrest 73
(7) Paragraph (c)(2). A flat surface within the 35-inch head strike arc, such as a table or partition, may be tested to the criteria of Society of Automotive Engineers (SAE) J921 or the following criteria. Impact injury criteria is discussed in AC 21-22, Injury Criteria for Human Exposure to Impact. (Amendment 25-0)
(i) A 13-pound bowling ball may be used to simulate the head of a 170-pound person whose seat belt is fastened and is subjected to 9g. (Amendment 25-0)
(ii) The ball shall impact the surface with at least 2780-inch-pounds of energy.
(Amendment 25-0)
(iii) The attachments of the test article shall not fail completely. (Amendment 25-0)
(iv) No parts shall become loose or sharp projections be formed that would be hazardous to the passengers. (Amendment 25-0)
(v) The test article may deform locally. (Amendment 25-0)
(vi) The surface being tested should perform equal to or better than a previously approved surface. The intent of this comparative test method is to test similar items (e.g., a seatback that does not have a telephone with a seatback that has a telephone installed). This test method should not be used to compare a seatback to an armrest. (Amendment 25-0)
(8) Paragraph (c)(2). (Amendment 25-0)
(i) Some passenger seats are designed with armrests that pivot upward such that the armrest could protrude beyond the seatbacks resulting in a potentially hazardous condition to persons seated behind these seats. Armrests that are adequately delethalized or restricted such that they cannot protrude aft of either seatback in any position are acceptable. (Amendment 25-0)
(ii) Armrests that are offset can be within the headstrike path of an occupant to the rear. Armrests within the striking radius of the head that are:
(A) bounded on both sides of the armrest by the seat backs and are offset more than 2-inches from the armrests of the seat to the rear, or (B) forward of an additional (exposed) seat in the row behind it, such that the forward armrest is bounded on one side only are considered to be injurious objects. The head must be protected from these injurious objects by some additional means such as padding.
Armrests that are bounded only on one side and not offset from the armrest of the seat in the rear are not considered to be injurious objects. (Amendment 25-0)
(9) Paragraph (c)(2). The FAA issued policy memorandum 02-115-15, dated November 25, 2002, titled “New Policy with respect to compliance with § 25.785(d), Amendment 25-88, for certification of passenger seat armrests.” The policy in this
75 memorandum may be used for demonstrating compliance with § 25.785(c)(2), Amendment 25- 20, and is provided below. (Amendment 25-0)
(i) Armrests that might possibly be struck by persons seated behind (aft of) them are characterized as “bounded” or “unbounded.” Bounded armrests are defined as follows:
(A) An armrest that has a seatback on both sides, with the distance between the structure of the adjacent seatbacks no greater than five inches, or (B) An armrest that has a seatback on one side and the airplane sidewall panel or a wall that is part of an airplane furnishing (e.g., galley, closet, lavatory) on the other side with the distance between the structure of the seatback and the panel/wall no greater than five inches.
(ii) For purposes of this AC, the structure of the seatback is considered to be the parts of the seatback with load carrying capability. It does not include upholstery material or soft foam installed for occupant comfort. In some seat designs there is a metal frame in the seatback that forms the support structure to which the foam and upholstery are used to provide the shape of the seatback. When measuring the distance between the structure of the adjacent seatbacks of no greater than five inches, the measurement would be between these metal or composite supports structures.
(iii) Unbounded armrests are those that do not meet either definition above.
Additionally, seat places that are located aft of unbounded armrests may be characterized as either “exposed” or “non-exposed.” The non-exposed seat place is typically an aisle seat place,
i.e., located adjacent to a passenger aisle (refer to figure 83-3). The exposed seat place is typically located where the number of seats in the row forward is different from that of the seat row aft. For example, near Type III overwing exits, many airplanes have a double seat installed inboard of the exit with an empty space between the seat and the exit. The seat row aft of the double seat has a triple seat (refer to figure 83-4). In figure 83-4, seat place “A” is an exposed seat place that makes the outboard armrest of the double seat an unbounded exposed armrest.
(iv) The definitions above apply to all armrests in the airplane as applicable. The existing policy contained in this AC paragraphs 81b(5) and 81b(7) are still applicable to the armrests identified in the new policy below.
(A) Note: The policy below addresses armrests within the 35-inch head strike arc and surfaces 18-inches and greater above the floor. Armrests outside the 35-inch head strike arc and armrest surfaces less than 18-inches above the floor are acceptable as defined in this AC paragraphs 81b(5) and 81b(7).
(B) An armrest is acceptable by inspection if the armrests of two consecutive
(i.e., one aft of the other) seat assemblies (seats need not be of the same part number) are offset no greater 0.5-inch total, including design and production tolerances.
(C) Bounded armrests and non-exposed unbounded armrests are acceptable if:
(1) The armrests of two consecutive seat assemblies are offset greater than 0.5-inch but no greater than two (2)-inches total, including design, and production tolerances, and
(2) The breakover feature of the seatback(s) adjacent to the armrest in the forward seat assembly is (are) locked out.
(D) The seatback breakover feature may be locked out by any method that requires a tool to release the lock out provision. The lockout of the breakover feature must be effective for the seatback in the upright position used for taxi, takeoff, and landing. Seatbacks incorporating an energy absorbing feature to meet the HIC requirements of § 25.562 are considered to have the breakover lockout and are acceptable. Whatever the method of seatback breakover lock out, there typically is some movement of the seatback. This movement of the seatback is acceptable as long as when the seatback is moved to the worst case position by a small hand load applied to the top of the seatback, the armrest is still afforded protection by the seatback, with the end of the top of the armrest being forward of the aft side of the seatback.
(E) Bounded armrests and non-exposed unbounded armrests, where the offset is greater than two (2)-inches total, including design and production tolerances, need to be addressed as being injurious objects within the striking radius of the head, e.g., by padding the armrest.
(F) Exposed unbounded armrests; if the armrests of two consecutive seat assemblies that are offset by more than 0.5-inch total, including design and production tolerances, need to be addressed as being injurious objects within the striking radius of the head,
e.g., by padding the armrest.
(G) Armrests that are padded (using appropriate padding material as described in paragraph 81b(5) of this AC) must have the padding cover the length of the armrest that is encompassed by 35-inch and smaller head strike arcs. Bounded armrests, where the seatback(s) have the breakover feature locked out, need not be padded to encompass the entire 35-inch head strike arc because the seatbacks prevent the contact of the armrest on the forward side of the seatback(s). Therefore, these armrests need only be padded to the forward edge of the seatback(s) in their upright position achieved after the small hand force is applied to the seatback. Portions of the armrest surface that cannot be contacted by the head are not required to be padded, e.g., the lower (or under) surface of a curved armrest.
(H) As an alternative to the use of padding, surfaces within the striking radius of the head that translate out of the striking radius under a nominal (10 pound) load may be considered to provide adequate protection, e.g., armrests that have been pivoted upward, which pivot downward out of the head strike arc under the nominal load. During an evaluation of this feature, the load must be applied in a direction that approximates the motion of a seated and belted occupant in the seat aft of the armrest under crash conditions.
77 FIGURE 83-3 ARMREST OFFSET
FIGURE 83-4 NON-EXPOSED AND EXPOSED ARMREST
(10) Paragraph (d). The seat back may serve as a firm hand hold. Since many seats are capable of breaking over, the breakover load must be adequate to be considered firm. A load of 25 lbs minimum, acting horizontally, is considered adequate when applied at the top center of the seat back. (Refer to paragraph 411b.(10) for maximum breakover force.) Very large seat pitches (in excess of 65-inches) may not permit the seatbacks to act as a handhold. This is due to both distance between the seatbacks and the capability of the seats to have very large amounts of recline. In this case, it may be necessary to install supplementary features to serve as handholds.
Seat mounted headrests that move relative to the seatback do not need to be assessed for their ability to provide a firm handhold, provided the seatback remains available for use as a handhold, and meets the criteria identified above. Other interior features such as class dividers, closets and other monuments may also serve as acceptable handholds if they provide a surface for occupants to push against to steady themselves while moving about the cabin interior.
(Amendment 25-0)
(11) Paragraph (f). Each berth installation should include a seat belt located approximately at the occupant's pelvis. For a berth installation with the feet facing forward, a bag, enclosing the legs to catch the upper torso when subjected to 9g, would be satisfactory in lieu of a padded end board. If the head is facing forward, a strap over each shoulder configuration would be satisfactory. If the berth is side facing, a padded side board or two belts, located approximately at the thighs and approximately at the chest, would be satisfactory.
(Amendment 25-0)
(12) Paragraph (h). Flight attendant seats that are provided for the airplane configuration should be installed near the approved floor level emergency exits. This should not be interpreted as a requirement to install flight attendant seats at each floor level exit. "Near" is defined in AC 25.785-1A. (Amendment 25-0)
(13) Paragraph (i). In order to reduce the deceleration "g" forces on occupants, some forward facing seats are designed to collapse. Usually, the design incorporates collapsible front legs. Such is acceptable if the collapse does not occur until a minimum of 8g has been applied.
After the collapse has occurred, the ultimate load of 9g should be applied and maintained for the required three seconds. The activation of the energy absorbing feature should not result in occupant injury. Various dimensions, such as 35-inches to injurious object clearance, aisle width and clearance, and interference with exits, should be evaluated before and after activation of the energy absorbing feature. Required dimensional clearances, such as aisles, passageways, flight attendant assist spaces, exit opening envelopes, and clearance between seats and potentially injurious surfaces must be maintained after the energy-absorbing feature is activated. The final position of the seat should not trap occupants. When testing a seat to demonstrate compliance with the static requirements of § 25.561, the testing should be conducted with an occupant center of gravity (CG) location as defined in NAS 809 (referenced in Technical Standard Order (TSO) C39) and AS8049 (referenced in the current version of TSO-C127). This CG location should be utilized in any airplane interface load analysis conducted. (Amendment 25-0)
(14) Paragraph (i). Technical Standard Order (TSO)-C22 is applicable only to seat belts. Technical Standard Order C114 may be applicable to shoulder harnesses, or they may be
79 approved as part of the airplane. Sled tests with anthropomorphic dummies have shown that shoulder harness loads for forward facing seats can vary between 40 percent and 60 percent of the total load. Therefore, it is acceptable to substantiate a shoulder harness load of 60 percent (Refer to AC 25.785-1A, “Flight Attendant Seat and Torso Restraint System Installations,” dated 1/6/94): 0.6x9gx170 lbs = 918 lbs. If the seat belt is not approved under TSO-C22 or later revision, it should be approved as part of the airplane. The seat belt should be substantiated for 100 percent of the occupant load: 9g x 170 lbs = 1530 lbs. This is necessary even if the shoulder harness is permanently attached to the seat belt, since it is usually possible to utilize the seat belt without using the shoulder harness. The l.33 fitting factor is applicable to these configurations.
(Amendment 25-0)
(15) Paragraph (i)(1)(i). A seat is normally approved to TSO-C39 or later revision.
This approval may not account for the critical load when occupied by less than maximum occupants, e.g., one or two occupants in a triple seat. In some seat designs, occupancy by less than the maximum could be a critical design load for a particular structural member. All possible combinations of seat place occupancy should be substantiated by test or analysis. The loads for underseat baggage restraint systems attached to the seat should be added to seat loads.
Refer to § 25.787 guidance for underseat baggage criteria. This can be done by the TSO manufacturer when doing the TSO substantiation or by the applicant who is installing the seat.
(Amendment 25-0)
(16) Paragraph (i)(3). The l.33 factor is only required to be applied to the stated attachments. This factor should be applied to both ends of each attachment, (i.e., the seat end and the airplane end) and the fitting. If the applicant wishes to test the entire seat and belt assembly to this l.33 factor, it is satisfactory. (Amendment 25-0)
84. AMENDMENT 25-32, Effective May 1, 1972.
a. Regulation.
(a) Each seat, berth, safety belt, harness, and adjacent part of the airplane at each station designated as occupiable during takeoff and landing must be designed so that a person making proper use of these facilities will not suffer serious injury in an emergency landing as a result of the inertia forces specified in §§ 25.561.
(b) Each seat and berth must be approved.
(c) Each occupant of a seat that makes more than an 18 degree angle with the vertical plane containing the airplane centerline, must be protected from head injury by a safety belt and an energy absorbing rest that will support the arms, shoulders, head, and spine, or by a safety belt and shoulder harness that will prevent the head from contacting any injurious object. [Each occupant of any other seat must be protected from head injury by a safety belt and, as appropriate to the type, location, and angle of facing of each seat, by one or more of the following:
(1) A shoulder harness that will prevent the head from contacting any injurious object.
(2) The elimination of any injurious object within striking radius of the head.
(3) An energy absorbing rest that will support the arms, shoulders, head, and spine.]
(d) If the seat backs do not have a firm hand hold, there must be a hand grip or rail along each aisle to enable occupants to steady themselves while using the aisles in moderately rough air.
(e) Each projecting object that would injure persons seated or moving about the airplane in normal flight must be padded.
(f) Each berth must be designed so that the forward part has a padded end board, canvas diaphragm, or equivalent means, that can withstand the static load reaction of the occupant when subjected to the forward inertia force specified in § 25.561.
Berths must be free from corners and protuberances likely to cause serious injury to a person occupying the berth during emergency conditions.
(g) Each crewmember seat at flight deck stations must have provisions for a shoulder harness. These seats must meet the strength requirements of paragraph (i) of this section.
(h) Cabin attendant seats must be in the passenger compartment near approved floor level emergency exits.
(i) Each seat berth, and its supporting structure, must be designed for an occupant weight of 170 pounds, considering the maximum load factors, inertia forces, and reactions between the occupant, seat, and safety belt or harness, at each relevant flight and ground load condition (including the emergency landing conditions prescribed in § 25.561). For berths, the forward inertia force must be considered in accordance with paragraph (f) of this section and need not be considered with respect to the safety belt. In addition-
(1) The structural analysis and testing of the seats, berths, and their supporting structures may be determined by-
(i) Assuming that the critical load in the forward, sideward, downward, and rearward directions (as determined from the prescribed flight, ground, and emergency landing conditions) acts separately; and
(ii) Using selected combinations of loads if the required strength in each specified direction is substantiated;