APPENDIX 3. SEAT FAMILY DEFINITION (CONTINUED) Label changes OK without retest Buckle changes OK without retest, if Color changes OK load path is unchanged (e.g. finish or without retest opening angle) Webbing material Changes to length on side changes require OK without retest Internal mechanism retest changes require retest Most closure mechanism changes OK without retest (no changes to the load path) Figure A3-4 Seat Belts
12. Attachments between Structural Members.
a. Family of seat principles. Fittings and fasteners provide the primary load path between structural components. These include, but are not limited to, the connection method of the spreader-to-beam attachment, beam-to-leg attachment, and leg-to-track fitting attachment. In general, these attachments should reflect a similar design philosophy at similar locations within the seat assemblies (for example, the attachment method between the lateral beams and the seat legs should be consistent between seat assembles).
APPENDIX 3. SEAT FAMILY DEFINITION (CONTINUED)
b. Variations and post certification changes acceptable by analysis. Variations to the attachments between structural members due to space or geometry limitations are acceptable without additional tests provided:
• The attachment has the same design philosophy, and
• It can be shown by rational analysis that the strength and stiffness are equivalent to or less critical than the tested seat.
c. Variations and post certification changes requiring additional tests. An additional test(s) must be conducted for any seat with an attachment that reflects a different design philosophy (for example, a beam-to-leg attachment with a spreader clamp design versus a saddle design) from the seat included in the baseline testing.
(1) An additional test(s) must be conducted for any seat with an attachment that reflects the same design philosophy but is determined to be structurally more critical than the attachment between structural members of a similar seat included in the baseline testing.
(2) A single 16g longitudinal or 14g vertical test is sufficient to substantiate the attachment between structural members with a different design philosophy or variations within the same design philosophy, provided it can be determined which test condition is critical for that attachment.
13. Seat Track Fittings.
a. Family of seat principles. Seat track fittings are critical components in the primary load path. The seat track fitting provides the load path between the seat primary structure (for example, leg or beam) and the airplane structure (for example, seat track).
Seat track fittings must have the same load path and similar design philosophy.
b. Variations and post certification changes acceptable by analysis.
(1) Variations to the seat track fitting locking mechanism engagement or adjustment device (screw, bolt, etc.) are acceptable without additional analysis, provided it is not part of the load path or does not change the load path (for example, by altering stud engagement).
(2) Variations in seat track fitting finish are acceptable without additional analysis, provided the method of finish application does not affect the strength of the part.
APPENDIX 3. SEAT FAMILY DEFINITION (CONTINUED)
c. Variations and post certification changes requiring additional tests. Variations in seat track fitting geometry or method of attachment must be substantiated by test(s). An additional test(s) must be performed for any seat with a seat track fitting that has a variation in load path, material, manufacturing process, or construction method from the tested seat(s).
14. Energy Absorbers in Seat Leg Structures.
a. Family of seat principles.
(1) Energy absorbers (EA devices) are typically incorporated in the seat leg structure to control occupant or structural loads. Within a family, energy absorbers must share a consistent design. While the inco rporation of energy-absorbing features is encouraged, the criticality assessment is not as straightforward as for other parts of the primary load path.
(2) If all seat leg/EA combinations are identical, the normal seat dynamic test program that tests the structurally critical seat will also substantiate all the seat leg/EA combinations in this case. No additional tests are required.
b. Variations and post certification changes acceptable by analysis.
(1) When the seat leg structures are identical at all locations, but different rated EAs are at some seat leg locations (the EAs use the same design philosophy, and the EAs end attachments are identical), the leg structure must be substantiated for the highest load and the stroke of each EA device must be substantiated as follows:
(a) Substantiation of the leg structure and attachment. The normal seat dynamic test program that considers the structurally critical seat will also substantiate all the seat leg/EA combinations if none of the EAs stroke or if only the highest rated EA strokes. Either of these test results will en sure that the highest seat/floor interface loads were developed.
(b) Substantiation of the EA stroke. In general, a lower-rated EA device should not “bottom-out,” unless the highest rated EA also “bottoms-out.” In any event, additional tests may be required to test the lower-rated EA device(s) to establish the highest seat/floor interface load for that device, should any EA other than the highestrated EA “bottom-out” during the test.
(2) In all cases, additional tests must be performed critically testing the lowerrated EA devices, or the supplier must work with the appropriate regulatory agency to develop a validated predictive model for the EA devices in order to provide an adequate rational analysis in order to avoid additional tests.
APPENDIX 3. SEAT FAMILY DEFINITION (CONTINUED)
(3) The following steps outline the considerations to be used in performing a predictive rational analysis used to substantiate seat legs with different rated EA devices.
This analysis should be successfully completed prior to conducting dynamic tests in order to demonstrate that there is adequate testing of the energy-absorbing system and the affected seat structure:
1 2 3 Load to initiate device Stroke Load Level Maximum Stroke Maximum Load 4 Capability Load Displacement Figure A3-5
• The fundamental performance should be characterized in terms of the maximum load capability, the load to initiate the EA device, the stroking load level, and the amount of stroke/deformation available. These parameters all need to be determined.
• Using the static interface loads and knowledge of the EA characteristics, the expected stroking load level and stroke length should be predicted.
• The analytical predictions and the results of the dynamic test should be correlated to ensure that during the dynamic test all EAs have performed as designed.
• It should be demonstrated that none of the seat/EA combinations would bottom out under their maximum load case.
APPENDIX 3. SEAT FAMILY DEFINITION (CONTINUED) NOTE: EA variations that do not aff ect the fundamental performance or make the stroke/deformation of the EA more critical may be allowed without retest.
c. Variations and post certification changes requiring retest. If a seat assembly has different leg structure and different rated EAs at some locations, each seat leg/EA combination must be demonstrated by tests to produce the maximum seat/floor interface load for each individual seat leg/EA combination. This is necessary to ensure that the maximum seat leg/EA load is developed for each combination and that adequate stroke is available at each individual EA.
15. Seat backs.
a. Family of seat principles. The seat back supports the occupant’s torso in the seated position. It is the com ponent of the seat that is typically forward of an occupant in a row-to-row HIC situation (forward facing seats) and is the component of the seat that provides the load path to the lower seat structure in aft-facing installations. The permanent deformation of seat backs can be a significant consideration for the occupant egress of the airplane. The primary cons iderations for this component regarding variations/ are the effects on seat back position/angle and occupant positioning (which may affect HIC or lumbar load), the effect on structural performance, and seat back permanent deformation.
(1) The components installed on the seat back (for example, food tray tables, video monitors and telephones) must be represented when evaluating variations as well as the recline mechanism, breakover devices, seat back energy-absorbers, and seat back attachment hardware.
(2) The seat back structural components and attachment hardware must have the same materials, manufacturing processes, and construction method, and they must be similar in geometry.
(3) The seat back energy-absorbers must be the same for all seat backs for all seats that are subject to the HIC criteria.
(4) The seat back breakover must be the same for all seat backs for all seats that are subject to the HIC criteria.
(5) When a load is applied to the seat back in the upright position, the load path within the recline mechanism from the seat back to the seat structure must be the same for all seat backs that are subject to the HIC criteria.
(6) Seat backs should be interchangeable between most families, if the seat back accessories, back structure, and method of attachment perform the same.
APPENDIX 3. SEAT FAMILY DEFINITION (CONTINUED)
(7) Once substantiated for HIC, seat backs can be arranged independently in the airplane, provided the installation limitations of the new arrangement result in comparable conditions to those under which the target seat was tested (simple analysis demonstrates that no new head strike features are in the head strike zone). For example, once the business class seats pass the HIC testing, they can be installed in the airplane with an economy class seat behind without further substantiation. Exceptions include pairing with a seat with very unusual performance, for example, very large deformation or substantial energy-absorption.
b. Variations and post certification changes acceptable by analysis. Variations to components installed on the seat back are acceptable without additional test(s), provided the test article selection process in paragraph 5 of this AC (considering the component variance) shows the seat selected for the row-to-row HIC tests is the seat that was tested.
(1) Variations to the attachment method of components installed on the seat back are acceptable without additional test(s) as follows:
(a) For retention, it can be shown by rational analysis that the strength is equivalent to or less critical than the tested seat(s), and
(b) This does not replace the test discussed in paragraph 5 of this AC for row-to-row HIC
(2) Variations to the seat back, excluding potential head contact areas, that do not significantly affect the mass/weight, center of gravity, or load path stiffness of the seat back (for example, cushion trim or dress cover) are acceptable without additional analysis.
(3) Variations of the seat back structure width up to 2 inches are allowed without additional test, as long as these variations in seat width do not introduce new structure in the target head strike area. Variations greater than 2 inches may require additional test(s) for HIC and B/C deformation.
(4) Variations in the seat back upright position of ±3 degrees are acceptable, provided it can be shown that the variation has no influence on occupant egress from the airplane when evaluated using the seat permanent deformation data from the baseline tests. For example, applying the seat permanent deformations from the baseline tests to the “new” seat back upright position still meets the guidance given in Appendix 2 for occupant egress, including ‘B’ vs. ‘C’. Add itional variations in the upright position are acceptable with analysis that the variations do not influence HIC or egress for either the person in the seat or the person behind the seat.
(5) Variations to backrest cushion hardness and contour are acceptable, provided the SRP does not vary by more than 0.75 inch from the SRP of the tested seat.
APPENDIX 3. SEAT FAMILY DEFINITION (CONTINUED)
(6) Variations to any part of the recline mechanism that do not provide a load path from the seat back to the seat structure are acceptable without additional analysis.
c. Variations and post certification changes requiring retest. Variations in the seat back structure materials, manufacturing processes, or construction method from the tested seat(s) may require retest.
(1) A HIC test(s) may be necessary for any seat with a seat back subject to the HIC criteria that has a variation in an installed component. Use the test article selection process in ¶ paragraph 5of this AC to determine whether the component variance must also be tested.
(2) A test(s) must be performed for the following seats, if they are required to meet the HIC criteria:
(a) Any seat with a seat back that has a variation in the attachment method of an installed component that has been determined to be more critical than the tested seat(s).
(b) Variations in the seat back attachment method which the test article selection process in paragraph 5 of this AC shows must be tested in addition to previously tested seat(s).
(c) Variation in the seat back energy absorber from the tested seat(s).
(d) Variation in the seat back breakover from the tested seat.
(e) Variation to any part of the recline mechanism that provides a load path from the seat back to the seat structure from the tested seat. If a part of the recline mechanism is not considered critical in the HIC load path, variations that do not lower the strength of the load path are acceptable without test. For example, the recline mechanism can be replaced with a “solid rod,” because other components in the HIC load path absorb the energy of a seat back head strike.
(f) Variation in backrest cushion hardness or contour that changes the SRP location more than 0.75 inch in any direction from the seat back to the seat structure from the tested seat.
(g) Variation in the seat back upright position of greater than ±3 degrees from the seat back to the seat structure from the tested seat, unless an acceptable analysis is provided per paragraph b. above.
APPENDIX 3. SEAT FAMILY DEFINITION (CONTINUED)
16. Seat Weight.
a. Family of seat principles. The seat weight has a significant influence on the seat performance during the structural tests. Sma ll weight variations are acceptable, but large increases must be substantiated by test. These variations are accounted for in the critical test case evaluation by interface load comparison. Proper planning of test article definition and testing can make accommodation of future seat weight growth. This can be accomplished by adding ballast to the test article.
b. Variations and post certification changes acceptable by analysis.
(1) An increase in the weight of a seat that was included in the baseline testing is acceptable without additional test or analysis, provided the increase is not greater than 3 percent of the total unoccupied tested seat system weight.
(2) An increase in the weight of a seat that was not included in the baseline testing (that is, a seat that was not tested per the test article selection process) is acceptable provided:
(a) The test article selection process in paragraph 5 of this AC using a seat interface load analysis with the increased seat weight shows the seat(s) selected for the structural tests to still be the tested seat(s).
(b) If the weight increase to any seat is due to adding a specific item to a specific location on the seat, see Appendix 5 of this AC for guidance on the method of substantiation
(c) Depending on the location of the added component, testing of the component in question may be conducted on a partial or unoccupied seat. These types of tests should be coordinated in advance with the appropriate regulatory agency.
(d) Testing must have substantiated HIC, if ATD head contact with the added item is possible.
(e) Testing must have substantiated lumbar load, if ATD contact with the added item is possible.
c. Variations and post certification changes requiring additional tests. An additional test must be added to the baseline testing for any seat that was included in the baseline testing with a weight increase greater than 3% of the unoccupied tested system seat weight.
APPENDIX 3. SEAT FAMILY DEFINITION (CONTINUED)
(1) An additional test(s) must be performed for any seat that was not included in the baseline testing with a weight increase, if the test article selection process in paragraph 5 of this AC, using a seat interface load analysis with the increased seat weight, determines that this seat should be selected for testing.
(2) An additional test(s) must be performed for any seat with a weight increase due to adding a specific item to a specific location that was not substantiated in the baseline testing for HIC, or lumbar load (as appropriate).
NOTE: See Appendix 5 for discussion of acceptable methods of substantiation for retention of an item of mass on the seat.
17. Armrests.
a. Families of seat principles. Armrests are the seat structures that retain the occupant’s sides. They are not required f eatures on a seat, and many passenger places can have armrests on one or both sides of the passenger stowed (folded up). The primary considerations for this component regarding variations or changes are the effect on retention of the component, HIC (head contact on the aft part of the armrest from occupant seated behind), occupant egress of the airplane (seat permanent deformations), and positioning of the occupant in the seat place.
b. Variations and post certification changes acceptable by analysis. Variations to armrests are allowed provided:
(1) It can be shown by rational analysis that the variations have no influence on the ATD dynamic response.
(2) It can be shown by rational analysis that the variations have no influence on occupant egress from the airplane when evaluated using the seat permanent deformation data from the baseline tests (see AC 25.562-1A).
(3) The test article selection process in Section 4.0, considering the seat with the armrest geometry variance, show the seat(s) selected for the row-to-row HIC tests have been tested.
(4) Variations to the armrest attachment can be shown by rational analysis that the strength is equivalent to or less critical than the tested seat(s).
c. Variations and post certification changes requiring additional tests. Variations to armrests that are in a potential occupant head-strike location should be substantiated by test or analysis.
APPENDIX 3. SEAT FAMILY DEFINITION (CONTINUED)
(1) An additional test(s) must be added for any seat that has an armrest that has a variation in attachment method that is determined to be more critical with regard to strength than the seat(s) included in the baseline testing.
(2) An additional test(s) may be required, if changes to the armrests influence the ATD response to lumbar loads. For exampl e, if the seat geometry forces the ATD’s arms over the armrests during a test and a post-test modification to the armrest would significantly change the ATD response, an additional test may be required.
(3) An additional row-to-row HIC test may be required , if geometry or material variations to the armrest in any seat are within the ATD head contact area from an occupant in the seat behind.
APPENDIX 4. PROCEDURE FOR DEMONSTRATING COMPLIANCE WITH
HIC FOR REPETITIVE SEAT ROWS
1. In an effort to reduce the regulatory burden and clarify the procedure for demonstrating compliance, the following procedure has been developed. In the majority of cases, this procedure should allow demonstration of compliance for HIC with two tests. The procedure takes into account seat pitch, the relative position of the seat and the row behind it, and the range of occupant seated heights (5th percentile female to 95th percentile male). The intent of this procedure is to provide default conditions that can be used in lieu of conducting several tests or performing lengthy analytical studies. Observe that seats that have homogenous impact surfaces (for example, those with a shell or integral partition) may require only one HIC test. For installations that incorporate airbags or upper torso restraints, a similar approach could be used provided that the applicant conducts a specific analysis for two basic contact areas to assess HIC. Specific attention should be given to the range of occupants required for airbags.
a. For Each Family of Seats:
(1) Identify the intended seat installation configurations from a seat-to-seat HIC perspective. This will typically include seats in parallel or repetitive rows but may also include other factors, such as:
(a) Seats on canted seat tracks, such that the seats are parallel to each other, but are at an angle with respect to the airplane’s longitudinal axis.
(b) Seats on laterally staggered seat tracks, such that the seat places, rowto-row, are staggered.
(c) Non-parallel seat rows.
(d) Laterally staggered seating due to a change in the number of seat places.
(e) Different width seats that result in the seat places, row-to-row, being slightly staggered.
(2) Identify the range of intended seat-to-seat pitch.
NOTE: For non-parallel seat installations (e.g., at the seat track break between the airplane constant and tapered sections) the SRP-to-SRP distance at the center of the seat place will be used as the seat pitch to determine minimum and maximum pitch when utilizing this test article selection procedure. All seat places (inboard to outboard) in the seat must be considered when determining the minimum and maximum seat pitch.
Additional, unique seat pitches may be considered by choice.
(3) For two of the same part number seats in the family, installed parallel to each other:
APPENDIX 4. PROCEDURE FOR DEMONSTRATING COMPLIANCE WITH
HIC FOR REPETITIVE SEAT ROWS (CONTINUED) Fwd Strike point to hit seat back or arm rest Max Pitch Seat Back Arm Rest Figure A4-1
(a) Determine the maximum seat pitch (within the range identified in step 1(a)(2))) and the yaw angle (within the ±10 degrees envelope plus additional seat installation angle per step 1(a)(1)(a), if required) at which the 50% male ATD head impacts (i.e., solid strike, not glancing blow) the lower portion of the seat back structure and/or the armrest structure. In most cases, the additional aircraft installation angle is not additive to both the plus and minus yaw angle (for example, the analysis for an aircraft installation angle may be +10 degrees and –14 degrees).
(b) Conduct a test of the seat pitch and yaw angle per paragraph (a) of this paragraph with the yaw direction, such that the ATD head strikes the side of the seat with the seat recline mechanism (Zone A test).