d. Installation of instrumentation. Professional practice should be followed when installing instrumentation. Care should be taken when installing the transducers to prevent deformation of the transducer body that could cause errors in data. Lead -wires should be routed to avoid entanglement with the ATD or test article, and sufficient slack should be provided to allow motion of the ATD or test article without breaking the lead-wires or disconnecting the transducer. Calibration procedures should consider the effect of long transducer lead-wires. Head accelerometers and femur load cells should be installed in the ATD in accordance with the ATD specification and the instructions of the transducer manufacturer.
The load cell between the pelvis and the lumbar column should be installed in accordance with the approach shown in Figure 2 of this AC, or in a manner that will provide equivalent data (see paragraph 8b).
(1) If an upper torso restraint is used, the tension load should be measured in a segment of webbing between the ATD's shoulders and the first contact of the webbing with hard structure (the anchor point or a webbing guide). Restraint webbing should not be cut to insert a load cell in series with the webbing, since that will change the characteristics of the restraint system. Load cells that can be placed over the webbing without cutting are commercially available. They should be placed on free webbing to minimize contact with hard structure, seat upholstery, or the ATD during the test. They should not be used on double -reeved webbing, multiple -layered webbing, locally stitched webbi ng, or folded webbing, unless it can be demonstrated that these conditions do not cause errors in the data. These load cells should be calibrated using a length of webbing of the type used in the restraint system. If the placement of the load cell on the webbing causes the restraint system to sag, the weight of the load cell can be supported by light string or tape that will break away during the test.
(2) Since load cells are sensitive to the inertial forces of their own internal mass and to the mass of fixtures located between them and the test article, as well as to forces applied by the test article, it may be necessary to compensate the test data for that inaccuracy if the error is significant. Data for such compensation will usually be obtained from an additional dynamic test that replicates the load cell installation, but does not include the test item.
e. Restraint system adjustment. The restraint system adjustment should be made as follows:
The restraint system shall not be tightened beyond the level that could reasonably be expected in use, and the emergency locking device (inertia reel) shall not be locked prior to the impact. Automatic locking retractors shall be allowed to perform the webbing retraction and automatic locking function without assistance. Care shall be taken that emergency locking retractors that are sensitive to acceleration do not lock prior to the impact test because of preimpact acceleration applied by the test facility. If comfort zone retractors are used, they shall be adjusted in accordance with instructions given to the user of the restraint system.
(1) If manual adjustment of the restraint system is required, slack shall be removed, and the restraint system should be snug about the ATD. For test 2, this can normally be determined when two fingers will fit snugly between the belt and the pelvis of the ATD. The restraint system shall be checked and adjusted just prior to the floor deformation phase of the test.
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(2) If the system is tested in other than a "horizontal floor" position, the restraint should be properly adjusted with the seat in the "horizontal floor" position and the webbing transducers installed (if required). After sufficient time has elapsed to allow the cushion to reach an equilibrium position, the webbing should be marked to indicate the correct adjustment point. The seat and ATD should then be installed on the fixture in the appropriate dynamic test orientation and the restraint system again adjusted to that same point.
(3) An alternate method to impose a 1 -g preload is to measure the position of the ATD hip joints relative to the floor as shown in Figure 7 below. The ATD is then depressed into the cushion to reproduce this relative position after the ATD and seat have been installed on the fixture, as shown in Figure 8. The lap belt may be tightened to maintain this position. This load may make it impossible to insert two fingers between the lap belt and the pelvis of the ATD, but it should not produce a cushion displacement in excess of that measured by placing the ATD on the seat in a 1-g orientation.
f. . A floor is not required for Test 2 , but if a floor is installed, it should not influence the behavior of the seat, or unduly restrict the movement of the ATD's feet. This is a concern especially when floor distortion is applied. For consistency, a floor should be used for tests used to-gather head path data.
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Gravity Vector Figure 7. Measurement of 1g Preload Par 11 27
Velocity Vector Figure 8. Test Orientation, 1g Position 28 Par 11
12. DATA REQUIREMENTS . The data should include charts, listings, and/or tabulated results, and copies of any photo instrumentation used to support the results. The following should be recorded:
a. Impact pulse shape
b. Head Injury Criterion (HIC) results for all ATD's exposed to head impact with interior components of the airplane or head strife paths and velocities if head impact is likely but could not be evaluated by these tests
c. Total velocity change
d. Upper torso restraint system load, if applicable
e. Compressive load between the pelvis and the lumbar column
f. Retention of upper torso restraint straps, if applicable
g. Retention of pelvic restraint
h. Femur loads, if applicable
i. Seat attachment (including structural damage)
j. Seat deformation
k. Seat attachment reaction time histories I. Retention of items of mass
m. Post test retrieval of life vest
n. Evaluation of seat egress
13. DATA ANALYSIS .
a. General. All data obtained in the dynamic tests should be reviewed for errors. Baseline drift, ringing, and other common electronic instrumentation problems should be detected and corrected before the tests. Loss of data during the test is readily observed in a plot of the data versus time and is typically indicated by sharp discontinuities in the data, often exceeding the amplitude limits of the data collection system. If these occur early in the test in essential data channels, the data should be rejected and the test repeated. If they occur late in the test after the maximum data in each channel has been recorded, the validity of the data should be carefully evaluated, and the maximum values of the data may still be acceptable for the tests described in par 12 29
this AC. The HIC does not represent simply a maximum data value, but an integration of data over a varying time base. The head acceleration measurements used for that computation are not acceptable if errors or loss of data are apparent in the data at any time, from the beginning of the test until the ATD and all test articles are at rest after the test.
b . Impact pulse shape. Data for evaluating the impact pulse shape is obtained from an accelerometer that measures the acceleration in the direction parallel to the inertial response shown in Figure 1 of this AC. The impact pulses intended for the tests discussed in this AC have an isosceles triangle shape. These ideal pulses are considered minimum test conditions. Since the actual acquired test pulses will differ from the ideal, it is necessary to evaluate the acquired test pulses to insure the minimum requirements are satisfied. The five properties of the ideal pulse that must be satisfied by the acquired test pulse are as follows (see Figure 1):
Pulse shape: isosceles triangle Greq: peak deceleration required by test condition Treq: rise time required by test condition V: total velocity change required by test condition Vtr: velocity change required during Treq (Vtr = V/2) A graphical technique can be used to evaluate pulse shapes that are not precise isosceles triangles. Appendix 1 of this AC presents the graphical method of evaluating the acquired pulse (the recorded test sled acceleration versus time).
For the acquired pulse to be acceptable, the following five criteria must be met:
(1) The magnitude of the peak value for the acquired pulse, Gpk, must be greater than or equal to Greq.
(2) The actual rise time, T r = T2 - T1, must be less than or equal to Treq.
(3) The result of integrating the acquired pulse during the interval from t = T 1 to t = T 3 must be equal to or greater than V tr, one-half of the required velocity change for the specified test. If the magnitude of the acquired pulse is greater than the ideal pulse during the entire interval from T 1 to T 3, this requirement is automatically met.
(4) The result of integrating the acquired pulse during the interval from t = T 1 to t = T 1 + 2.3 (Treq) must equal or exceed the required test velocity change, V, of the test condition. If the acquired pulse returns to zero g's at t = T 4 < (T1 + 2.3 (Treq)), the end of the interval of integration is reduced to t = T 4.
(5) If the magnitude of the acquired pulse is greater than the ideal pulse during the entire interval of t = T1 to T2, and the parameters of paragraphs (1) through (4) above are satisfied, then the acquired pulse is acceptable.
(6) If the magnitude of the acquired pulse is not greater than the ideal pulse during the entire interval t = T 1 to T 2, the difference between acquired pulse and the ideal must be no greater than 2.0 g's at those times when the acquired pulse is less than the ideal. The 30 Par 13
parameters of paragraphs (1), (2), and (3) above must also be satisfied for the acquired pulse to be acceptable.
c. Total Velocity Change. Impact velocity can be obtained by measurement of a time interval and a corresponding sled displacement that occurs just before or after (if appropriate) the test impact, and then dividing the displacement by the time interval. When making such a computation, the possible errors of the time and displacement measurements shall be used to calculate a possible velocity measurement error, and the test impact velocity should exceed the velocity shown in Figure 1 by at least the velocity measurement error. If the sled is not changing velocity during the immediate preimpact or postimpact interval, the impact velocity is the total velocity change. If the sled is changing velocity during the immediate pre -impact or post -impact interval, or if the facility produces significant rebound of the sled, the total velocity change can be determined by integrating the plot of sled acceleration versus time, as described in Appendix 1. If this method is used, the sled acceleration shall be measured in accordance with Channel Class 180 requirements.
d. Head Injury Criterion (HIC).
(1) Data for determining the Head Injury Criterion (HIC) need to be collected during the tests discussed in this AC only if the ATD's head is exposed to an impact on airplane interior features (not including the floor or the ATD's own leg) during the test. The HIC is calculated according to the following equation:
Where: tl and t 2 are any two points in time (in seconds) during the head impact, and a(t) is the resultant head acceleration (expressed in g's) during the head impact.
(2) The HIC is a method for defining an acceptable degree of occupant head injury. The HIC should not exceed 1000, for head impact against interior surfaces in a crash.
(3) The HIC is invariably calculated by computer based data analysis systems, and the discussion that follows outlines the basic method for computation . The HIC is based on data obtained from three mutually perpendicular accelerometers installed in the head of the ATD in accordance with the ATD specification. Data from these accelerometers are obtained using a data system conforming to Channel Class 1000, as described in SAE Recommended Practice J211. Only the data taken during head impact with the airplane interior need be considered;
this is usually indicated in the data by a rapid change in the magnitude of the acceleration. Film of the test may show head impact that can be correlated with the acceleration data by using the time base common to both electronic and photographic instrumentation. Simple contact switches that do not significantly alter the surface profile could also be used to define the initial contact time.
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(4) The magnitude of the resultant acceleration vector obtained from the three accelerometers is represented' as a function of time. Then, beginning at the time of initial head contact (t 1), the average value of the resultant acceleration is found for each increasing increment of time (t 2-t1), by integrating- the curve between t1 and t2 and then dividing the integral value by the time (t 2-tl). This calculation should use all data points provided by the minimum 8000 samples per second digital sampling rate for the integration. However, the maximizing time intervals need be no more precise than 0.001 seconds. The average values are then raised to the 2.5 power and multiplied by the corresponding increment of time (t 2-t1).
(5) This procedure is then repeated, increasing t 1 by 0.001 seconds for each repetition. The maximum value of the set of computations obtained from this procedure is the HIC. The procedure may be simplified by noting that the maximum value will only occur in intervals where the resultant magnitude of acceleration at t 1 is equal to the resultant magnitude of acceleration at t 2, and when the average resultant acceleration in that interval is equal to 5/3 times the acceleration at t 1 or t 2. The HIC is usually reported as the maximum value, and the time interval during which the maximum value occurs is also given.
(6) In many cases, a full system sled test to evaluate specific occupant injury conditions may not be needed to evaluate a redesign of the seat system that affects only HIC. In such cases, the photometric head path data can be gathered and used to ensure no contact will occur, or to define the head angle and velocity at impact.
These data can used in a component test of severity comparable to the whole system sled test. Other factors, such as the inertial response of the impact target,. must be accounted for in the component test condition so that the impact condition is representative. Component testing methods must be demonstrably comparable to whole system sled tests as a HIC measure, and the specific methodology used will require approval by the FAA.
Additionally, a seat may be designed for use in multiple locations where head contact against a range on unknown bulkhead targets is anticipated (e.g., front row seats). For these seats, HIC may be measured using a representative impact target mounted in front of the seat at the installation setback, or range of setbacks. This target will represent typical fixtures such as galleys, partitions, lavatories, and closets, and its stiffness wil be representative for those monuments. If contact occurs, the HIC must be < 1000.
e Upper torso restraint system load. The maximum load in the upper torso restraint system webbing can be obtained directly from a plot or listing of webbing load transducer output. If a three-axis load transducer, fixed to the test fixture, is used to obtain these data, the data from each axis shall be combined to provide the resultant vector magnitude. If necessary, corrections shall be made for the internal mass of the transducer and the fixture weight it supports. This correction will usually be necessary only when the inertial mass or fixture weight is high, or when the correction becomes critical to demonstrate that the measurements fall below the specified limits.
f. Compressive load between the pelvis and lumbar column . The maximum compressive load between the pelvis and the lumbar column of the ATD can be obtained directly 32 Par 13
from a plot or listing of the output of the load transducer at that location. Since most load cells will indicate tension as well as compression, care should be taken that the polarity of the data has been correctly identified.
g. Retention of upper torso restraint straps. Retention of the upper torso restraint straps on the ATD's shoulders can be verified by observation of photometric or documentary camera coverage. The straps must remain on the ATD's shoulder until the ATD rebounds after the test impact and the upper torso restraint straps are no longer carrying any load. The straps must not bear on the neck or side of the head and must not slip to the upper rounded portion of the upper arm during that time period.
h. Retention of pelvic restraint . Retention of the pelvic restraint on the ATD's pelvis can be verified by observation of photometric or documentary camera coverage. The pelvic restraint shall remain on the ATD's pelvis, bearing on or below each prominence representing the anterior superior iliac spine, until the ATD rebounds after the test impact and the pelvic restraint becomes slack. Provided that the pelvic restraint remains on the ATD's pelvis, traping of the belt between the leg and the pelvis is acceptable.
Movement of the pelvic restraint above the prominence is usually indicated by an abrupt displacement of the belt onto the ATD's soft abdominal insert which can be seen by careful observation of photo data from a camera located to provide a close view of the belt as it passes over the ATD's pelvis. This movement of the belt is sometimes indicated in measurements of pelvic restraint load (if such measurement are made) by a transient decrease or plateau in the belt force, as the belt slips over the prominence, followed by a gradual increase in belt force as the abdominal insert is loaded by the belt.
i . Femur load. Data for measuring femur loads can be collected in the tests discussed in this AC if the ATD's legs contact seats or other structure. Data need not be recorded in each individual test, if rational comparitive analysis is available for showing compliance.
14. PAS SNAIL CRITERIA. The dynamic impact tests shall demonstrate that:
a. Since the test methods described in this AC are ultimate load condtions, damage to the seat and restraint is expected. The regulation specifically accounts for yielding as an acceptable form of permanent damage. In addition, the following should be considered:
(1) The seat system remains attached to the test fixture at all points of attachment, the occupant restraint system remains attached at all points of attachment and the primary load path remains intact. For the purpose of showing compliance with the structural requirements of § 25.562, acceptable damage to the load -carrying structural elements include: bending deformation, tension deformation, compression crippling, and shear buckling. Cracking of structural elements and the shearing or separation of rivets and minor delamination of composite panels is allowed provided a continuous load path remains between the occupant and the seat attachments.
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(2) Damage to seat belts, such as scuffing, fraying and breakage of fibers is considered acceptable. The seat belt should not be cut, or torn by features of the seat or the belt adjuster mechanism. Cuts or tears should be investigated as to their cause, and appropriate corrective action taken, although a retest may not be necessary.
b. If the ATD's head is exposed to impact with interior features during the test, a HIC of 1,000 is not exceeded.
c. Where upper torso restraint straps are used, tension loads in individual straps do not exceed 1,750 lbs.(7.78 kN). If dual straps are used for restraining the upper torso, the total strap tension load does not exceed 2,000 lbs.(8.90 kN) .
d. The maximum compressive load measured between the pelvis and the lumbar column of the ATD does not exceed 1,500 lbs. (6.67 kN).
e. The upper torso restraint straps (where installed) remain on the ATD's shoulder during impact.
f. The pelvic restraint remains on the ATD's pelvis during impact.
g. Where leg contact with seats or other structure occurs, the axial compressive load in each fem ur does not exceed 2,250 lbs. (10.0 kN).
h. The seat permanent deformations are within the quantitative limits of Appendix 2 of this AC and will not significantly impede an occupant from releasing his restraints, standing, and exiting the seat. In no case should deformation of the seat cause entrapment of the occupant, whether or not the defined limits referenced in Appendix 2 are exceeded.
NOTE: It is assumed that the maximum seat deformation will result from the structural evaluation (i.e., single row Type 2 test). Once this is accomplished, it would not, therefore, be considered necessary to repeat deformation measurements after the injury criteria (multiple row) tests, unless the structural and injury criteria tests were combined into one test.
i. All deployable items must remain stowed, unless it can be shown that they do not impede egress or cause serious injury (see Appendix 2).
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 12 of this AC, the documentation should include the following:
(1) Facility data.
(i) The name and address of the test facility performing the tests.
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(ii) The name and telephone number of the individual at the test facility responsible for conducting the tests.
(iii) A brief description and/or photograph of each test fixture.
(iv) The date of the last instru mentation system calibration and the name and telephone number of the person responsible for instrumentation system calibration.
(v) A statement confirming that the data collection was done in accordance with the recommendations in this AC, or a detailed description of the actual calibration procedure used and technical analysis showing equivalence to the recommendations of this AC.
(vi) 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.
(vii) A description of the photographic -instrumentation system used in the tests.
(2) Seat restraint system data.
(i) 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. Qualifying approvals, such as Technical Standard Order (TSO) authorizations, should be included.
(ii) 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.
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(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 shoul d be documented. This could include use 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. 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. These models can vary in complexity from simple spring-mass dynamic models to exceedingly complex models, which can be of help in designing 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. The Federal Aviation Administration will continue to assess the performance of dynamic computer models, and will issue appropriate advisory material should any of these techniques be found to be useful alternatives to the tests discussed in this AC.