15. TEST DOCUMENTATION.
a. General. The tests should be documented in reports that describe the procedures, limitations, results, and deviations to the tests discussed in this AC. In addition to the specific data requirements specified in paragraph 9 of this AC, the documentation should include the following:
(1) Facility data.
(a) The name and address of the test facility performing the tests.
(b) The name and telephone number of the individual at the test facility responsible for conducting the tests.
(c) A brief description and/or photograph of each test fixture.
(d) A statement confirming that all instrumentation and data collection equipment used in the test meet the facility’s internal calibration requirements, that these calibration requirements are documented and available for inspection upon request, that all calibrations are traceable to a national standard, and that the records of current calibration of all instruments used in the test are maintained at the facility.
(e) A statement confirming that the data collection was done in accordance with the recommendations in this AC or a detailed description of the actual procedure used and technical analysis showing equivalence to the recommendations of this AC.
(f) The manufacturer, governing specification, serial number, and test weight of the ATDs used in the tests, and a description of any modifications or repairs performed on the ATDs that could cause them to deviate from the specification.
(g) A description of the photographic-instrumentation system used in the tests.
(2) Seat restraint system data.
(a) The manufacturer's name and identifying model numbers of the seat restraint system used in the tests with a brief description of the system, including identification and a functional description of all major components and photographs or drawings, as applicable. Qu alifying approvals, such as Technical Standard Order (TSO) authorizations, should be included.
(b) For systems that are not symmetrical, an analysis supporting the selection of most critical conditions used in the tests.
b. Test Description. The description of the test should be documented in sufficient detail, so that the tests could be reproduced simply by following the guidance given in the report. The procedures outlined in this AC can be referenced in the report but should be supplemented by such details as are necessary to describe the unique conditions of the tests. For example:
(1) Pertinent dimensions and other details of the installation that are not included in the drawings of the test items should be provided. This can include footrests, restraint system webbing guides and restraint anchorages, “interior surface” simulations, bulkhead or sidewall attachments for seats or restraints, etc.
(2) The floor deformation procedure, guided by goals of most critical loading for the test articles, should be documented.
(3) The placement and characteristics of electronic and photographic instrumentation chosen for the test beyond that information provided by the facility should be documented. This can include special targets, grids, or marking used for interpretation of photo documentation, transducers, restraint system loads, floor reaction forces, or other measurements beyond those discussed in this AC.
(4) Any unusual or unique activity or event pertinent to conducting the test should be documented. This could include us e of special “break away” restraints or support for the ATDs, test items or transducers, operational conditions or activities such as delayed or aborted test procedures, and failures of test fixtures, instrumentation system components, or ATDs.
(5) Any energy-absorbing features that are intended as part of the design and the expected structural behavior that will result should be documented.
16. COMPUTER MODELS.
a. Several computer models have been developed to represent the seat restraint/occupant system in a crash. Some of these models include representation of the vehicle interior as well. Models vary in complexity from simple spring-mass dynamic models to exceedingly complex models, that can help design an entire work station.
Validation of these models also varies from no validation at all to complex validation efforts based on controlled testing and field experience. The use of these models during the design phase of seat restraint/interior systems for civil airplanes is encouraged. They can be of great assistance in predicting “most critical” conditions, in understanding the performance of systems when used by various sized occupants, in estimating head strike paths and velocities, and for many other uses of interest to the designer.
b. Advisory Circular 20-146 Methodology for Dynamic Seat Certification by Analysis for Use in Part 23, 25, 27, and 29 Airplanes and Rotorcraft provides criteria for the use of analytical modeling techniques and guidance on methods of compliance using computer models. We will continue to assess the performance of dynamic computer models and will continue to issue appropriate advisory material as these techniques are found to be useful alternatives to the tests discussed in this AC.
APPENDIX 1. PROCEDURES FOR EVALUATING PULSE SHAPES
1. This graphical procedure may be used to evaluate the impact pulse shape acquired from a test. While this procedure is based on graphical concepts, an accurate evaluation of the pulse parameters should be obtained using the digitized data and computer algorithms that provide the analysis illustrated in the following steps:
Figure A1-1 55
APPENDIX 1. PROCEDURES FOR EVALUATING PULSE SHAPES (CONTINUED)
2. On the plot of the acquire pulse, identify the peak deceleration point, Gpk, and points on the onset of the pulse equal to 0.1 Gpk and 0.9 Gpk. Construct an onset line through the points 0.1 Gpk and 0.9 Gpk. Extend th e constructed onset line to the base line of the data plot, G=0. Identify the in tersection of the constructed onset line and baseline as the start of the acquired pulse, T1. For the acquired pulse to be acceptable, the magnitude of Gpk must equal or exceed the minimum required pulse, Greq for the specified test condition.
Figure A1-2
3. Using T1 as the start time, construct the ideal pulse required for the test condition.
Draw a vertical line and a horizontal line through the peak of the ideal pulse, Greq. The vertical line through Greq will intersect the time axis at the maximum allowed rise time, T3. Draw another vertical line at the first intersection of the horizontal line through Greq and the acquired pulse after T1. This vertical line will intersect the time axis at T 2. The actual rise time, Tr = T2 - T1, must be less than or equal to Treq for the acquired pulse to be acceptable.
APPENDIX 1. PROCEDURES FOR EVALUATING PULSE SHAPES (CONTINUED)
4. Compute the velocity change, Vra, of the acquired pulse during the interval T1 to T3. Observe that T 3 will usually occur after the peak, Gpk, of the acquired pulse. For the acquired pulse to be acceptable, Vra must be at least one-half the total velocity V, required for the specified test condition.
5. If the total velocity change for the test is calculated from the acquired pulse, use the interval starting at T1 and ending:
a. At the point T4, defined as where the acquired pulse first intersects the baseline, G = 0, after the time of Gpk, or
b. At the time equal to: T1+2.3xTreq, whichever occurs first.
Figure A1-3 57
APPENDIX 1. PROCEDURES FOR EVALUATING PULSE SHAPES (CONTINUED) Figure A1-4
6. Construct a line parallel to the ideal (minimum regulatory requirement) pulse and offset by 2 g in magnitude less than the ideal during the time interval between T1 and T3.
Likewise construct a line parallel to the ideal pulse and offset by 2 g in magnitude less than the ideal (minimum regulatory requirement) pulse on the trailing side of the pulse from:
T3 < t < T 1 + 1.33( T3- T1) 58
APPENDIX 1. PROCEDURES FOR EVALUATING PULSE SHAPES (CONTINUED) If the magnitude of the acquired pulse is 2 g less than the ideal pulse shape at any point along the acquired pulse shape during the period T1 < t < T 1 + 1.33( T3- T1), the pulse is unacceptable. As an example, the 16 g test specified for Test 2 in 14 CFR 25.562 has a rise time (T3 - T1) of 90 milliseconds. For a test pulse to be in compliance with the 16 g test pulse, the magnitude of the acquired pulse can be no less than 2 g from the ideal pulse during the time interval from T1 < t < (T1 + 120) milliseconds. The acquired pulse shown in Figure A1-5 is unacceptable because the acquired pulse magnitude is more than 2 g below the tolerance band during the onset period.
Sled Impact Pulse Time (Milliseconds) 0 50 100 150 200 250 300 350
5.0
0.0 -5.0 -10.0 -15.0 -20.0 g 120 MS Ideal Pulse 2 g Unacceptable Figure A1-5 59
APPENDIX 2. SEAT DEFORMATION
1. GENERAL. Seats may deform due to either the action of discrete energy absorber systems included in the design or to plastic deformation of their structural components.
If this deformation is excessive, it could impede the airplane emergency evacuation process. Each seat design may differ in this regard and should be evaluated according to its unique deformation characteristics. If floor deformations are applicable, consistency in pre and post-test measurements must be maintained. If the pre-test measurements are made before floor deformations are applied, the post-test measurements must be made after floor deformations have been removed. Conversely, if the pre-test measurements are made after floor deformations are applied, the post-test measurements shall be made before removal of floor deformations.
2. FIXED SEATS. The following post-test deforma tions and limitations regarding emergency exit egress may be used for showing compliance with §§ 25.561(d) and
25.562(c)(8). Dimensions specified for unde formed seat rows assume the maximum permanent deformation discussed below and are given to enable evaluation of an installation without having to make reference to test reports. In those cases where the actual permanent deformations are less than maximum, the specified dimensions for undeformed seat rows could be correspondingly decreased (except where clearance is specified for aisles, passageways, etc.).
a. Forward or Rearward Directions. Seats that exhibit forward or rearward deformations should not exceed a maximum of 3.0 inches (75 mm). In this case, the minimum clearance between undeformed seat rows, measured as shown in Figure A2-1 of this appendix, should be 9.0 inches (228 mm) or, alternatively, 6.0 inches (150 mm), plus the actual fore/aft deformation. Seat rows that lead to Type III exits are subject to the specific access requirements for those exits. This will result in greater spacing at those seat rows in the undeformed case. For seats with deformations that exceed 3.0 inches, the undeformed clearances should be increased accordingly.
In addition, at seat rows leading to Type III or IV exits, 20 inches (508 mm) minimum clearance, measured above the arm rests, must be maintained between adjacent seat rows.
At other seat rows, the most forward surface of the seat back shall not deform to a distance greater than one half the original distance to the forward-most hard structure on the seat (see Figure A2-2 of this appendix). These measurements may be made on the center line of the seat with the seat backs returned to their upright position, using no more than original seat back breakover forces, typically 25-35 pounds (111-155 N).
b. Downward Direction. There is no limit on downward permanent deformation, provided that the feet or legs of occupants will not be trapped by the deformation.
c. Seat Rotation. The seat bottom rotational perm anent deformation must not result in an angle that exceeds 20 degrees pitch down or 35 degrees pitch up from the horizontal plane. This rotational deformation is measur ed between the fore and aft extremities of 60
APPENDIX 2. SEAT DEFORMATION (CONTINUED) the seat pan at the centerline of each seat bottom (see Figure A2-3 of this appendix).
Rotation of the seat pan must not entrap the occupant.
d. Sideward Direction.
(1) The deformed seat should not encroach more than 1.5 inches (38 mm) into the required longitudinal aisle space at heights up to 25 inches (635 mm) above the floor.
The determination of which parts of the seat are at what heights is determined prior to testing.
(2) The deformed seat should not encroach more than 2.0 inches (50 mm) into the longitudinal aisle space at heights 25 inches (635 mm) or more above the floor.
e. Additional Considerations. In addition, none of the above deformations may permit the seat to:
(1) Affect the operation of any emergency exit or encroach into an emergency exit opening for a distance from the exit not less than the width of the narrowest passenger seat installed in the airplane.
(2) Encroach into any required passageway.
(3) Encroach more than 1.5 inches (38 mm) into any cross-aisle or flight attendant assist space.
f. Deployable Items. Certain items on the seat, such as food trays and legrests, are used by passengers in flight and are required to be stowed for taxi, takeoff, and landing.
Deployment of such items should be treated as “permanent deformation” if the item deploys into an area that must be used by multiple passengers (in addition to the occupant of the seat) for egress. Such deployments can be considered acceptable, even if they exceed the dimensions specified in paragraphs (a) through (e) above, if they are readily pushed out of the way by normal passenger movement and then remain in a position that does not affect egress. Small items, such as cup holders, ash trays, and trim pieces, are not considered a significant impedance to egress and do not require evaluation as a deployed item. (See also Appendix 5.)
3. STOWABLE SEATS. Stowable seats that may impe de egress must stow post-test and remain stowed to the extent necessary in order to satisfy the criteria as applied to fixed seats in paragraphs 2(a) through(d) and 2(e)(2) and (3) of this Appendix.
a. Seats that are Stowed Manually. A post-test stowage force no greater than 10 pounds (45 N) above the original stowage force may be used to stow the seat.
APPENDIX 2 SEAT DEFORMATION (CONTINUED)
b. Seats that Stow Automatically. A seat that may interfere with the opening of any exit must automatically retract to a position where it will not interfere with the exit. For determining encroachment into passageways, cross-aisles, and assist spaces, a post-test stowage force no greater than 10 pounds (45 N), applied at a single point, may be used to assist automatic retraction.
A A Measurement to be taken over full width of seat bottom cushion Figure A2-1 B C Pre-test Condition Post-test Condition Dimension “C” must be at least 50 percent of Dimension “B” Figure A2-2 62
APPENDIX 2 SEAT DEFORMATION (CONTINUED) A A Pan pitch down;
angle not to exceed 20°
SECTION A-A Pan pitch up;
angle not to exceed 35o
SECTION A-A Figure A2-3 Maximum Post-test Seat Pan Rotation 63