(2) Substantiation of the 14g download condition for each family of seats:
Step 1. Determine the 14g downward static interface loads (or any other standard load) for all seats. Compare the aft fitting resultant loads of all seats in the family, regardless of the number of legs on the seat, and identify the seat with the highest load.
This will usually be the same seat that was selected for the critical forward structural test.
This one seat will be tested.
Step 2. Conduct a 14g vertical dynamic test of the seat selected above.
Step 3. Use full occupancy for this test. This is to ensure that the maximum compressive load is put on the structure.
Step 4. Install the mass of life vests and literature pocket contents at each seat place, regardless of seat occupancy. Ballast may be used for non-critical parts of the seat (for example, under seat In-Flight Entertainment (IFE) boxes). However, if this test is also used to acquire lumbar loads, the criticality of parts should be assessed with that in mind. (See paragraph e(2)(b) discussion below regarding compliance with § 25.562(c)(2).)
NOTE: Weights representing under-seat baggage are not required for the 14g vertical test. The ATDs identifie d in the § 25.562(c)(2) part of this test selection process should be instrumented to collect lumbar loads.
Step 5. Retention of a specific item of mass, including emergency equipment, need be demonstrated only once during the 14g vertical load condition, if suitable retention using the production means of attachment is shown by dynamic test. The item of mass may be restrained for all other 14g vertical tests.
Step 6. Include a representative floo r in the test setup for the ATD’s feet.
NOTE: Refer to paragraph a(1) above to address special design features (for example, unique energy-absorption features).
e. Injury Criteria (see §§ 25.562(c)(1) to (c)(6)). Injury criteria may be either measured during tests used to show compliance with other requirements or in dedicated tests, depending on the seat design and the practicality of acquiring the necessary data.
(1) Section 25.562(c)(1) - Upper torso restraint tension loads.
(a) The upper torso restraint tension loads must be collected during a structural test where the seat is yawed in the direction that produces the highest tension load in the restraint system. Typically th is is the yaw direction that puts the upper torso restraint over the shoulder of the ATD which is moved further forward as a result of the yaw.
(b) If the 16g longitudinal test that demonstrates compliance with § 25.562(c)(7) is yawed in the appropriate direction, the restraint tension load data may be collected during this test, and an additional test is not required.
(c) If the 16g longitudinal test that demonstrates compliance with § 25.562(c)(7) is not yawed in the appropriate direction, an additional test must be added to the baseline testing. The test article for the additional test is the same seat selected for the 16g longitudinal test that demonstrates compliance with § 25.562(c)(7). It is yawed in the direction that creates the highest tension load in the restraint system, with the pitch and roll selected using the guidance in this AC.
(2).Section 25.562(c)(2) - Lumbar loads.
(a) The ATD lumbar loads must be collected during the 14g vertical test that demonstrates compliance with § 25.562(c)(7). An additional test for collecting lumbar loads is not required in the baseline testing (except as noted in paragraph (b) ).
(b) ATDs instrumented to measure lumbar loads must be placed in seat places that represent the stiffest load path from the center of the occupant place to the structure and the least-stiff load path from the occupant place to the structure. This requirement will typically result in two instrumented ATDs, but will not exceed three instrumented ATD locations in a single test.
NOTE: See paragraph a(1) to addres s special design features (for example, unique energy-absorption features) that may function differently, depending on seat occupancy.
If there is an item (for example IFE) or structure located at a specific seat place (typically beneath the seat pan) that may influence lumbar loads due to seat deflection and/or ATD contact, then lumbar loads must be addressed and substantiated for this location in addition to the locations identified above. These loads may be addressed and substantiated by either data showing no contact or an additional test(s) added to the baseline testing.
(3) Section 25.562(c)(3) - Upper torso restraint remains on shoulder.
(a) For seats with a single upper torso restraint (for example, a 3-point restraint), a test may be required which demonstrates that the upper torso restraint strap remains on the ATD’s shoulder during impact with the seat yawed in the most critical direction.
Typically, this is the yaw direction that puts the upper torso restraint over the shoulder of the ATD which is moved aft as a result of the yaw. (See Figure 5-3).
(b) If the 16g longitudinal test that demonstrates compliance with § 25.562(c)(7) is yawed in the appropriate direction so that the restraint is over the trailing shoulder, the restraint retention may be demonstrated during this test. An additional baseline test is not required.
FWD Restraint trailing occupant (Overhead view) Figure 5-3. Restraint Trailing Occupant
(c) If the 16g longitudinal test that demonstrates compliance with § 25.562(c)(7) is not yawed in the appropriate direction and the criteria discussed in paragraph 3b(3) cannot be met, an additional test may be necessary. The test article for the additional test would be the same seat selected for the 16g longitudinal test. This demonstrates compliance with § 25.562(c)(7), yawed in the direction most critical for the restraint strap to remain on the ATD’s shoulder and with the pitch and roll selected in accordance with the guidance in this AC.
(d) For seats with a dual upper torso restraint, the 16g longitudinal test that demonstrates compliance with § 25.562(c)(7) is acceptable for demonstrating that the upper torso restraint straps remain on the ATD’s shoulder during impact. An additional baseline test is not required.
(e) High-speed test film or video of the test must be used to demonstrate that the upper torso restraint strap remains on the ATD’s shoulder during the impact.
(4) Section 25.562(c)(4) - Lap belt remains on pelvis. It must be demonstrated that the pelvic restraint remains on the ATD pelvis during the deceleration pulse, including after ATD rebound. Verification that the belt is on the ATD pelvis post-test is sufficient to demonstrate compliance. High- speed cameras may be used to demonstrate compliance, if the lap belt angle is greater than 55 degrees or less than 45 degrees.
Additional baseline tests are not required.
(5) Section 25.562(c)(5) - Head injury criterion (HIC). The HIC is applicable to all seats occupiable for takeoff and landing. Typically, seats located behind interior structure (front row seats) can be addressed in one test, since the potential contact surfaces tend to be homogeneous. Repetitiv e seat rows introduce more variables and typically require more than one test to demonstrate compliance.
(a) In an effort to reduce the regulatory burden and both simplify and clarify the procedure for demonstrating compliance, the procedure in Appendix 4 for row-to-row HIC 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 target seat and the occupied row behind it, and range of occupant sizes. 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. The procedure is covered in detail in Appendix 4 but relies on two basic contact areas to assess HIC. These areas are the center of the seat back and the lateral edges of the seat back/armrest. 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.
(b) Demonstration of compliance with the HIC should address seat pitch, occupant height (5th percentile female to the 95th percentile male), and yaw angle (up to ±10 degrees and any angle in between). The evaluation showing HIC of 1000 or less must be from an ATD head impact that is a solid strike and not a glancing blow. Dynamic tests are conducted with a 49 CFR part 572, Subpart B ATD (or equivalent) that is representative of a 50th percentile male occupant. For the purpose of addressing HIC for the height of a 95th percentile male occupant, 3 inches should be added to the ATD top of head when using rational analysis to select the critical HIC test to be conducted with a 49 CFR part 572, Subpart B ATD (or equivalent). This dimension should also be used to address the range of occupants when a test, or analysis based on test, at the installed pitch using a 49 CFR part 572, Subpart B ATD (or equivalent) results in a glancing blow.
Once a seat back is qualified for HIC, any seat could be installed aft of it, provided the installation limitations result in comparable conditions to those under which the seat was tested.
(c) Compliance with the HIC is dependent on the details of the seat design as well as the installation. Variations between seats in the contact surfaces will require evaluation by test, unless it can be shown that one surface is more critical than the other.
With respect to installation, there are several considerations:
• Seats on canted seat tracks such that the seats are parallel but at an angle with respect to the airplane longitudinal axis.
• Seats on staggered seat tracks such that the seat places row-to-row are staggered.
• Non-parallel seat rows.
• Staggered seating due to a change in the number of seat places.
• Different width seats that result in seat places row-to-row that are slightly staggered.
(d) Front row seats are those located directly aft of a partition, monument, or any other commodity certificated to 9g. Seats located directly aft of seat-related furniture such as consoles and walls of pod seats are not considered front row seats. For front row seats, simpler methods of compliance are possible. These methods specifically limit the range of occupant evaluation for HIC to that strictly covered by the test in § 25.562(b).
1 Perform dynamic testing as prescribed in § 25.562(b) with no head contact or HIC of 1000 or less. A glancing blow resulting in HIC of 1000 or less is acceptable and would not require additional analysis or testing using a more conservative test set up.
2 Perform a dynamic test as described in Appendix 4, paragraph 2, of this AC to determine the head path arc of the 49 CFR part 572, Subpart B ATD or equivalent and install the seat such that no contact by the ATD head would occur. In this case, we would not require more analyses or repositioning of the seat.
3 For seats that incorporate head path reducing features according to the note below, seats may be qualified without a head path test as follows: For seats typically identified as “economy” class seats during air carrier operations, place the seats 42 inches or more from the potential contact point. For all other “front row” seats (e.g., first or business class) the setback distance must be 45 inches or more. When using these dimensions, applicants should coordinate with the FAA or designee, as appropriate, and provide suitable justification for FAA evaluation. No dynamic test is needed for HIC or head path arc for seats that follow a design philosophy that includes the use of metallic components in the primary load path from the seat beams through the seat legs. The distance is measured from the cushion reference point to the vertical plane at the aft most potential contact point.
NOTE: The specific dimensions selected are based on data from certification programs using seats designed to be installed in the front row, i.e., “front row seats.” These seats are different from other seats in the airplane, in that in order to minimize head path, they incorporate stiffer structure, or low stretch seatbelts, or combinations of similar features. This makes a front row seat distinct from other seats. Thus, the validity of the 42"/45" criteria is based on the type of seats from which that criteria was derived. Using the same criteria for typical (non-front row) seats has not been validated and could result in these seats having head paths greater than the specified amount. This is contrary to the rule and policy. The intent of the allowance is to eliminate a test, but at the same time maintain the level of safety intended, had the test been conducted.
f. Deformation for Egress. The seat permanent deformations (see Appendix 2) must be measured in all structural tests. In addition, seat-back permanent deformations 20
must be measured in a test where the ATD’s head contacts the seat back (for example, a row-to-row HIC test). All measured permanent deformations should be used to show compliance with § 25.562(c)(8). (However, deformations that occur as an artifact of test set-up orientation need not be considered.) Some of the seat permanent deformations will be evaluated for acceptability as part of the dynamic test results (seat pan rotation, ‘B’ vs.
‘C’). Some of the seat permanent deformations will be used by the seat installer to evaluate the seat installation and airplane interior configuration (seat forward, aft, side deformations, seat back forward and aft deformations, and deployment of deployable items). The seat installer must use the measured seat permanent deformations to show an acceptable installation with regard to occupant egress of the airplane.
6. TEST FACILITIES.
a. General. There are a number of test facilities that can be used to accomplish dynamic testing. These are grouped into categories, based on the method used to generate the impact pulse (that is, accelerators, decelerators, or impact with rebound), and whether the facility is a horizontal (sled) design or a vertical (droptower) arrangement.
Each facility type has characteristics that have advantages or disadvantages for the dynamic tests discussed in this AC. One particular concern with test facilities is the rapid sequence of acceleration and deceleration that takes place in tests. In an airplane crash, the acceleration phase is always gradual and usually well separated in time from the deceleration (crash) phase. In a test, the deceleration always closely follows the acceleration. When assessing the utility of a facility for the specific test procedures outlined in this AC, it is necessary to understand the possible consequences of this rapid sequence of acceleration and deceleration.
b. Deceleration Sled Facilities. In an airplane crash, the impact takes place as a deceleration, so loads are applied more naturally in test facilities that create the test impact pulse as a deceleration. Since it is simpler to design test facilities to extract energy in a controlled manner than to impart energy in a controlled manner, several different deceleration sled facilities can be found. The deceleration sled facility at the Federal Aviation Administration’s Civil Aeromedical Institute (CAMI) was used in developing the test procedures discussed in this AC.
(1) The acceleration phase of the test, where sufficient velocity for the test impact pulse is acquired, can distort the test results if the acceleration is so high that the test articles or ATDs are moved from their intended pre-test position. This inability to control the initial conditions of the test would directly affect the test results. This can be avoided by using a lower acceleration for a relatively long duration and by providing a coast phase (in which the acceleration or deceleration is almost zero) prior to the impact.
As a result, any dynamic oscillation in the test articles or the ATD which might be caused by the acceleration would decay.
(2) To guard against errors in data caused by pre-impact accelerations, data from the electronic test measurements (accelerations, loads) should be reviewed for the time period just before the test impact pulse to make sure all measurements are at the baseline (zero) level. Photometric film taken of the test should also be reviewed to make 21
certain that the ATDs used in the test and the test articles were all in their proper position prior to the test impact pulse.
(3) The horizontal test facility readily accommodates forward-facing seats in both tests discussed in this AC, but problems can exist in positioning the test ATDs in Test 1 if the seat is a rearward-facing or side-facing seat. In these cases, the ATDs tend to fall out of the seat due to the force of gravity and must be restrained in place using break-away tape, cords, or strings. Since each installation will present its own problems, there is no simple, generally applicable guidance for doing this. Attention should be given to positioning the ATD against the seat back and to proper positioning of the ATD’s arms and legs. It will probably be necessary to build special supports for the break-away restraint, so that the supports will not interfere with the function of the seat and restraint system during the test. Film taken of the test should be reviewed to make sure that the break-away restraint did break (or become slack) in a manner that did not influence the motion of the ATD or the test articles during the test.
c. Acceleration Sled Facilities. Acceleration sled facilities, usually based on the Hydraulically controlled Gas Energized (HYGE) accelerator device, provide the impact test pulse as a controlled acceleration at the beginning of the test. The test item and the ATDs are installed facing in the opposite direction from the velocity vector (i.e., opposite from the direction used on a deceleration facility) to account for the change in direction of the impact. There should be no problem with the ATD or the test items being out of position due to pre-impact sled acceleration, since there is no sled movement prior to the impact test pulse.
(1) After the impact test pulse, when the sled is moving at the maximum test velocity, it must be safely brought to a stop. Most of the facilities of this design have limited track length available for deceleration, so that the deceleration levels can be relatively high and deceleration may begin immediately after the impact test pulse.
(2) Since the dynamic response of the system follows the impact test pulse in time, any sled deceleration that takes place during that response will affect the response and change the test results. The magnitude of change depends on the system being tested, so that no general “correction factor” can be specified. The effect can be minimized if the sled is allowed to coast without significant deceleration until the response is complete.
(3) If the seat or restraint system experiences a structural failure during the test pulse, the post-impact deceleration can increase the damage and perhaps result in failures of unrelated components. This will complicate the determination of the initial failure mode and make product improvement more difficult.
(4) One other consideration is that the photometric film coverage of the response to impact test pulse must be accomplished when the sled is moving at near maximum velocity. On-board cameras or a series of track-side cameras are usually used to provide film coverage of the test. Since on-board cameras frequently use a wide angle lens placed close to the test items, it is necessary to account for the effects of distortion and parallax when analyzing the film.
(5) The acceleration sled facility faces the same problems in accommodating rearward facing or side-facing seats in Test 1 as the deceleration sled facility, and the corrective action is the same for both facilities.
d. Impact-with-rebound Sled Facilities. One other type of horizontal test facility used is the “impact-with-rebound” sled facility. On this facility, the impact takes place as the moving sled contacts a braking system which stores the energy of the impact and then returns the stored energy back to the sled, causing it to rebound in the opposite direction.
This facility has the advantage over acceleration or deceleration facilities in that only one half of the required velocity for the impact would need to be generated by the facility (assuming 100 percent efficiency). Thus, the track length can be shortened, and the method of generating velocity is simplified. The disadvantages of this facility combine the problems mentioned above for both acceleration facilities and deceleration facilities.
Since one of the reasons for this type of facility is to allow short track length to be used, it may be difficult to obtain sufficiently low acceleration just before or after the impact pulse to resolve data error problems caused by significant pre-impact and post-impact accelerations.
e. Drop Towers. Vertical test facilities can include both drop towers (decelerators) and vertical accelerators. Vertical accelerators that can produce the long duration/displacement impact pulse depicted in Figure 3-1 have not been generally available. However, drop towers are one of the easiest facilities to build and operate and are frequently used. In these facilities, the pull of earth’s gravity is used to accelerate the sled to impact velocity so that the need for a complex mechanical accelerating system is eliminated. Unfortunately, these facilities are difficult to use for conducting Test 2, particularly for typical forward-facing seats. In preparing for this test, the seat must be installed at an angle such that the ATD tends to fall from the seat due to gravity. The restraint system being tested cannot hold the ATD against the seat unless tightened excessively and will not usually locate the head, arms, or legs in their proper position relative to the seat. Design and fabrication of an auxiliary “break-away” ATD positionin g restraint system just for this test is a complex task. The auxiliary restraint must not only position the ATD against the seat (including maintaining proper seat cushion deflection) during the pre-release condition of 1g, but must also maintain the ATD in that proper position during the free fall to impact velocity when the system is exposed to 0g. It must then release the ATD in a manner that does not interfere with the ATD response to impact. The usual sequence of 1g/0g impact—without the possibility of a useful “coast” phase as done in horizontal facilities—causes shifts in initial conditions for the test impact pulse that can affect the response to the impact. The significance of this will depend on the dynamic characteristics of the system being tested, and these are seldom known with sufficient accuracy to enable the response to be corrected. In addition, the earth’s gravity will oppose the final rebound of the ATDs into the seat back, so that an adequate test of seat back strength and support for the ATD cannot be obtained. The problems in Test 1 or with rear-facing seats in Test 2 are not as difficult because the seat will support the ATD occupant prior to the free fall. However, the 0g condition that exist s prior to impact will allow the ATD to “float” in the seat restraint system, perhaps changing position and certainly changing the initial impact conditions. Again, use of an auxiliary break-away restraint system to correct these problems is difficult.
7. ANTHROPOMORPHIC TEST DEVICES.
a. General. The tests discussed in this AC were developed using modified forms of the ATDs specified by the United States Code of Federal Regulations, Title 49, Part 572 Anthropomorphic Test Dummies, Subpart B – 50th Percentile Male (known as the Hybrid II). These “Part 572B” AT Ds have been shown to be reliable test devices that are capable of providing reproducible results in repeated testing. However, since ATD development is a continuing process, provision was made for using “equivalent” ATDs.
Instrumented ATD types should not be mixed when completing the tests discussed in this AC. Any approved ATD type can be used when occupying the seat as ballast
b. Modification to Measure Pelvic/Lumbar Load.
(1) To measure the axial compressive load between the pelvis and lumbar column due to vertical impact as well as downward loads caused by upper torso restraints, a load (force) transducer is inserted into the ATD pelvis just below the lumbar column. There is a load cell available for this purpose that does not require major alteration to the ATD.
The general installation is shown schematically in Figure 7-1.
(2) ATDs modified per prior methods involving installation of a femur load cell, described in previous versions of this AC, continue to be acceptable for use.
(3) Alternative approaches to measuring the axial force transmitted to the lumbar spinal column by the pelvis are acceptable if the method:
(a) Accurately measures the axial force but is insensitive to moments and forces other than that being measured;
(b) Maintains the intended alignment of the spinal column and the pelvis, the correct seated height, and the correct weight distribution of the ATD; and
(c) Does not alter the other performance characteristics of the ATD.
Lumbar Spine Load Cell
(Denton Model 1891
or equiv. shown)
Base Block
(Supplied with load cell) h Height Adjusting Shims Pelvis Casting Pelvis Accelerometer
Cavity
Figure 7-1 Installation of Pelvic-Lumbar Load Cell in Part 572B ATD
c. Other ATD Modifications.
(1) To prevent failure of the clavicle used in Part 572 Subpart B ATDs due to flailing, a clavicle of the same shape but of higher strength material can be substituted.
(2) Submarining indicators, such as electronic transducers, may be added on the ATD pelvis. These are located on the anterior surface of the iliu m of the ATD pelvis without altering its contour, and indicate the position of the pelvic restraint as it applies loads to the pelvis. These indicators provide a direct record that the pelvic restraint remains on the pelvis during the test and eliminate the need for careful review of highspeed camera images to make that determination.
d. Equivalent ATDs. The continuing development of ATDs for dynamic testing of seating restraint/crash-injury-protection systems is guided by goals of improved biofidelity (human-like response to the impact environment) and reproducibility of test results. A procedure to enable the use of a modified 49 CFR part 572, Subpart E (the Hybrid III) ATD has been developed and is documented in the Society of Automotive Engineers (SAE) Technical Paper 1999-01-1609. The significant differences from a certification standpoint are in the lumbar spine region. In addition, there are some mass distribution adjustments that are necessary. The Hybrid III has a higher degree of biofidelity, and other enhancements as compared to the Hybrid II. Alternatively, ATDs can be considered the equivalent of the Part 572B ATD if:
(1) They are fabricated in accordance with design and production specifications established and published by a regulatory agency that is responsible for crash injury protection systems;
(2) They are capable of providing data for the measurements discussed in this AC or of being readily altered to provide the data;
(3) They have been evaluated by comparison with the Part 572B ATD and are shown to generate similar response to the impact environment discussed in this AC; and
(4) Any deviations from the Part 572B ATD configuration or performance are representative of the occupant of a civil airplane in the impact environment discussed in this AC.
8. INSTRUMENTATION.
a. General.
(1) Electronic and photographic instrumentation systems must be used to record data for qualification of seats. Electroni c instrumentation should measure the test environment and measure and record data required for comparison of performance to pass/fail criteria.
(2) Photographic instrumentation should be used to document the overall results of tests. Photographic instrumentation should also be used to confirm that the pelvic restraint remains on the ATD's pelvis and that the upper torso restraint straps remain on the ATD's shoulder during impact. The photographs should also document that the seat does not deform as a result of the test in a manner that would impede rapid evacuation of the airplane by the occupants and that the seat remains attached at all points of attachment. For passenger seats with lap belt angles of between 45 and 55 degrees, submarining is typically not a problem. Fo r this reason, a second camera (for example, an overhead camera) for evaluation of submarining is not necessary.
b. Electronic Instrumentation. Electronic instrumentation should be accomplished in accordance with the Society of Automotive Engineers Recommended Practice SAE J211, “Instrumentation for Impact Tests,” using the sign convention of SAE J1733 “Sign Convention for Vehicle Crash Testing.” In this practice, a data channel is considered to include all of the instrumentation components from the transducer through the final data measurement, including connecting cables and any analytical procedures that could alter the magnitude or frequency content of the data. Each dynamic data channel is assigned a nominal channel class that is equivalent to the high frequency limit for that channel, based on a constant output/input ratio versus frequency response plot which begins at 0.1 Hz (+1/2 to -1/2 dB) and extends to the high frequency limit (+1/2 to -1 dB). Frequency respons e characteristics beyond this high frequency limit are also specified. When digitizing data, the sample rate should be at least five times the 3 dB cutoff frequency of the presample analog filters. Since most facilities set all presample analog filters for Channel Class 1000, and since the 3 dB cutoff frequency for channel class 1000 is 1650 Hz, the minimum digital sampling rate would be about 8000 samples per second. For the dynamic tests discussed in this AC, the dynamic data channels must comply with the following channel class characteristics:
(1) Sled or drop tower vehicle acceleration is measured in accordance with the requirements of Channel Class 60.
(2) Belt-restraint system and seat attachment reaction loads (when measured) are measured in accordance with the requirements of Channel Class 60. Loads in restraint systems that attach directly to the test fixture can be measured by three-axis load cells fixed to the test fixture at the appropriate location. These commercially available load cells measure the forces in three orthogonal directions simultaneously, so that the direction as well as the magnitude of the force can be determined. If desired, similar load cells can be used to measure forces at other boundaries between the test fixture and the test item, such as the forces transmitted by the legs of the seat into the floor track. It is possible to use independent, single axis load cells arranged to provide similar data, but care should be taken to use load cells that can withstand significant cross axis loading or bending without causing errors in the test data.
(3) ATD head accelerations used for calculating the Head Injury Criterion (HIC) are measured in accordance with the requirements of Channel Class 1000.
(4) ATD femur forces are measured in accordance with Channel Class 600.
(5) ATD pelvic/lumbar column force is measured in accordance with the requirements of Channel Class 600.
(6) The full-scale calibration range for each channel provides sufficient dynamic range for the data being measured.
(7) Digital conversion of analog data provides sample resolution of not less than 1 percent of full-scale input.