restraint system, or the system may be used in several applications with different interior configurations. In such cases, it will be necessary to document the head strike path and the velocity along the path. This will require careful placement of photo instrumentation cameras and location of targets on the ATD representing the ATD head center of mass so that the necessary data can be obtained. These data can be used by the interior designer to ensure that head impact with the interior will not take place or that if possible head impact occurs, it will remain within the limits of the HIC. In the event the head impacts the specific interior, the interior under evaluation should be subjected to an individual special test to measure the head impact or HIC. The test is done using a rigid 6.5-inch diameter spherical head form weighing 15 pounds, (which includes necessary mass to represent the neck and a portion of the torso). The center of the head form is guided along the previously determined head strike path so that the form contacts the interior components at the velocity previously determined during the seat and torso restraint system dynamic test. Accelerometers located at the center of the head form would provide the data necessary for the HIC computation. If the interior component to be impacted by the ATD has significant inertial response to the impact environment, it will be necessary to evaluate those features or systems, such as breakover seatbacks or instrument panels designed to move forward, relative to the seat, in a dynamic test program which includes the full ATD occupant/seat/restraint system. See b.(3)(ii) of this guidance for ATD and panel location for adjustable crew seats.
(iii) Use of ATD. ATD used in the tests discussed in this guidance should be maintained to perform in accordance with the requirements described in their specification. Periodic teardown and inspection of the ATD should be accomplished to identify and correct any worn or damaged components, and appropriate ATD calibration tests (as described in their specification) should be accomplished if major components are replaced. Each ATD should be clothed in form -fitting cotton stretch garments with short sleeves, mid-calf length pants, and shoes (size 11E) weighing about 2.5 pounds.
The head and face of the ATD can be coated with chalk dust if it is desired to mark head contact areas on seats or other structure. The friction in limb joints should be set so that the joints barely restrain the weight of the limb when extended horizontally. The ATD should be placed in the seat in a uniform manner for reproducible test results. For the tests discussed in this guidance, the following procedures are adequate:
(A) The ATD should be placed in the center of the seat in as nearly a symmetrical position as possible.
(B) The ATD’s back should be against the seat back without clearance.
This condition can be achieved if the ATD’s legs are lifted as it is lowered into the seat.
Then, the ATD is pushed back into the seat back as it is lowered the last few inches into the seat pan. Once all lifting devices have been removed from the ATD, the ATD should be “rocked” slightly to settle it in the seat.
(C) The ATD knees should be separated about 4 inches.
Page C - 77
AC 29-2C, Chg 1 2/12/03 (D) The ATD hands should be placed on the top of the legs, just behind the knees. If tests on crew seats are conducted in a mockup with aircraft controls, the ATD hands should be lightly tied to the controls. If only the seat and occupant restraint system are tested, the ATD hands should be tied together with a lack cord that provides about 24 inches of separation before the cord becomes tight. This will prevent excessive arm flail during the ATD rebound phase.
(E) To the extent that they influence the injury criteria, all seat adjustments and controls should be in the design position intended for the 50th percentile male occupant. If seat and occupant restraint systems being tested are to be used in applications where requirements (placards) dictate particular positions for landing and takeoff, those positions should be used in the tests.
(F) The feet should be in the appropriate position for the type of seat tested (flat on the floor for a passenger seat or on control pedals or on a 45° footrest for flightcrew systems). The feet should be placed so that the centerlines of the lower legs are approximately parallel, unless the need for placing the feet on aircraft controls dictates otherwise.
(iv) 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 from causing errors in data.
Lead-wires should be routed to avoid entanglement with the ATD or test item, and sufficient slack should be provided to allow motion of the ATD or test item without breaking the lead wires or disconnecting the transducer. Calibration procedures should consider the effect of long transducer lead-wires. Head accelerometer (transducer) 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 spinal column should be installed as shown in Figure 29.562-4 of this guidance or in a manner that would provide equivalent data.
(A) An upper torso restraint is required by §29.785(b). 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 anchorage point or a webbing guide). Restraint webbing should not be cut to insert a load cell in series with the webbing, since that would change the characteristics of the restraint system.
Commercially available load cells can be placed over the webbing without cutting. They should be placed on free webbing and should not contact hard structure, seat upholstery, or the ATD during the test. They should not be used on double- reeved webbing, multiple-layered webbing, locally-stitched webbing, 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.
Page C - 78
(B) Loads in restraint systems attaching 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, or use careful (often complex) installation to protect the load cells from cross-axis loading or bending. 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 replicating the load cell installation but will not include the test item.
(v) Restraint system adjustment. The ATD should be sitting in the normal upright position. Care should be taken not to tighten the restraint system beyond the level reasonably expected in use and do not lock any emergency locking device (inertia reel) prior to the impact. Automatic locking retractors should be allowed to perform the webbing retraction and automatic locking function without assistance. Care should be taken that emergency locking retractors sensitive to acceleration do not lock prior to the impact test because of pre-impact acceleration applied by the test facility that is not present in a landing impact. If “comfort zone” retractors are used, they should be adjusted in accordance with instructions given to the user of the system. If manual adjustment of the restraint system is required, it should be sufficient to remove slack in the webbing, but it should not be adjusted so that it is unduly tight. Since the force required to adjust the length of the webbing can be as high as 11 pounds, a preload of 12-15 pounds is commonly recommended. This load is too small to be accurately measured by transducers selected to measure the high loads encountered in the impact test, so it should be measured manually as the restraint is being adjusted. Special gauges are commercially available to assist in this measurement. The preload should be checked and adjusted, if necessary, just prior to the floor deformation phase of the test.
(vi) Repetition of tests. It may be necessary to repeat the tests discussed in this AC if accurate data are not collected in critical data channels or if some other error occurs (e.g., cameras fail to operate, impact pulse inadequate, etc.). Preparation for a repeated test should follow the same steps as for the initial test. The seat should be removed from the fixture, and its attachment fittings or floor track examined and replaced, if necessary, to correct any damage. The ATD should be carefully examined and repaired or adjusted, if necessary. It is usually preferable to use a new seat and restraint system for all repeated tests to preclude system failures due to undetected damage. A new seat and restraint system should be used if there is any detectable variation from the intended design configuration.
Page C - 79
AC 29-2C, Chg 1 2/12/03
d. Data Analysis And Compliance With The Criteria
(1) 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 vs. 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, but the maximum values of the data may still be acceptable for the tests described in this guidance. The HIC does not represent a maximum data value, but represents an integration of data over a varying time base. The head acceleration measurements used for that computation should not be accepted 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.
(2) Impact pulse shape. Data for evaluating the impact pulse shape are obtained from an accelerometer that measures the acceleration in the direction parallel to the line of inertial response shown in Figure 29.562-1 of this guidance. The impact pulse intended for the tests discussed in this guidance has a symmetrical (isosceles) triangular shape. Since this ideal pulse is considered a minimum test condition, it is possible to evaluate the actual test pulse by comparing it with the ideal triangular pulse.
The ideal pulse can be drawn to scale on the data plot of the test sled or carriage acceleration vs. time. The test pulse is acceptable if the plotted data are equal to or greater than the ideal impact pulse. This method can lead to a practical necessity of exceeding the ideal pulse by a significant degree, unless the test facility has precise control in generating the test pulse. A graphic technique may be used to evaluate test impact pulse shapes that are not precise isosceles triangles. A graphic technique is contained in paragraph f. (1) of this guidance.
(3) Head Injury Criterion (HIC). Data for determining the HIC need to be collected during the tests discussed in this guidance only if the ATD’s head is exposed to secondary impact. The HIC is a method for defining an acceptable limit; i.e., the maximum values of the HIC should not exceed 1,000 for head impact against broad interior surfaces in a crash. The HIC is reported as the maximum value, and the time interval during which the maximum value occurs is also given. Most facilities will make this computation if requested. The HIC is calculated by computer -based data analysis systems because manual attempts to use this method with real data are likely to be tedious. The HIC is calculated according to the following equation:
Page C - 80
2.5 MAX Where: t 1 and t2 are any two points in the time range during the head impact. The range should not exceed 0.050 seconds, and a(t) is the resultant head acceleration at the center of gravity (expressed in g’s) during the head form impact.
(i) Data collection. The HIC is commonly 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 1,000 as described in SAE Recommended Practice J211. For the tests discussed in this guidance (both ATD and head form), only the data taken during secondary head impact with the aircraft interior need be considered. Head impact is often indicated in the data by a rapid change in the magnitude of the acceleration. Alternately, a film of the test may show head impact which can be correlated with the acceleration data by using the time base common to both electronic and photographic instrumentation, or simple contact switches on the impacted surface can be used to define the initial contact time.
(ii) HIC methodology. The following discussion outlines the basic method for computing the HIC. The magnitude of the resultant acceleration vector obtained from the three accelerometers is plotted against time. Then, beginning at the time of initial head contact (t1), the average value of the resultant acceleration is found for each increasing increment of time (t2 – t1), then integrating the curve between the range of t1 and t2 and then dividing the integral value by the time (t2 – t1). This calculation should use all data points provided by the minimum 8,000 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 (t2 – t1). This procedure is then repeated, increasing t1 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 t1 is equal to the resultant magnitude of acceleration at t2 and when the average resultant acceleration in that interval is equal to 5/3 times the acceleration at t1 or t2.
(iii) Limitations. HIC does not consider injuries that can occur from contact with surfaces having small contact areas or sharp edges, especially if those surfaces are relatively rigid. These injuries can occur at low impact velocities, and are often described as “cosmetic” injuries; however, they can involve irreversible nerve damage and permanent disfigurement. While there is no generally accepted test procedure to provide quantitative assessment of these injuries, a judgmental evaluation of soft tissue injuries can be made by assessing tears or cuts in a synthetic skin placed Page C - 81
AC 29-2C, Chg 1 2/12/03 over the ATD’s head or a head form during the test. Synthetic skins are discussed in the Society of Automotive Engineers Information Report SAE J202, Synthetic Skins for Automotive Testing.
(4) Impact velocity. Impact velocity can be obtained by measurement of a time interval and a corresponding sled displacement occurring just before or after (for acceleration facilities) 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 should be used to calculate a possible velocity measurement error, and the test impact velocity should exceed the velocity shown in Figure 29.562-1 by at least the velocity measurement error. If the sled is changing acceleration during the immediate pre-impact interval, or if the facility produces significant rebound of the sled, the effective impact velocity can be determined by integrating the plot of sled acceleration vs. time. If this method is used, the sled acceleration should be measured in accordance with Channel Class 180 requirements.
(5) 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 should be combined to provide the resultant vector magnitude. If necessary, corrections should 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.
(6) Compressive load between the pelvis and lumbar column. The maximum compressive load between the pelvis and the lumbar column of the dummy can be obtained directly 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.
(7) Retention of upper torso restraint straps. Retention of the upper torso restraint webbing straps on the ATD’s shoulders can be verified by observation of photometry or documentary camera coverage. The webbing should remain on the sloping portion of 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 webbing straps should not bear on the neck or side of the head and should not slip to the upper rounded portion of the upper arm during that time period.
(8) Retention of lap safety belt. Retention of the lap safety belt on the occupant’s (ATD) pelvis can be verified by observation of photometry or documentary camera coverage. The lap safety belt should remain on the ATD’s pelvis, bearing on or below each prominence representing the anterior superior iliac spines, until the ATD rebounds after the test impact and the lap safety belt becomes slack. If the lap safety belt does not become slack throughout the test, the belt should maintain the proper position throughout the test. Movement of the lap safety belt above the prominence is Page C - 82
usually indicated by an abrupt displacement of the belt into 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 lap safety belt load (if such measurements 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. Retention of the lap safety belt can also be verified by “submarining indicators” located on the ATD’s pelvis. These transducers are essentially a series of small, uncalibrated load cells placed in or above the rim of the ATD’s pelvis without changing its essential geometry. They indicate the position of the lap safety belt by producing an electrical signal when they are under load from the belt.
(9) Femur load. Measuring femur loads is not required by the rotorcraft standards. If a seat is installed in an aircraft in a manner that will expose the system to loads from an occupant seated behind the seat system as well as the occupant seated in the seat system, the tests discussed in this guidance should be conducted in a manner to demonstrate that the system will perform properly under the combined loading. For example, Test 2 should be conducted with at least two rows of seats in place, as the seats in the first row carry the loads from the occupants in the first row, as well as the leg kick loads from the second row (also noted in c.(3)(ii)(A) of this guidance).
(10) Seat attachment. Documentation that the seat and restraint system has remained attached at all points of attachment should be provided by still photographs that show the intact system components in the load path between the attachment points and the occupant.
(11) Seat deformation. Occupant seats evaluated in the tests discussed in this guidance can deform permanently, either due to the action of discrete (impact) energy absorber systems included in the design or due to residual plastic deformation of their structural components. If this deformation is excessive, it could impede emergency evacuation. Each seat design may differ in this regard and should be evaluated according to its unique deformation characteristics. Permanent seat deformations are measured on the critically loaded seat subsequent to conduct of the tests required in §29.562. The seat deformation is measured subsequent to completion of the dynamic tests and, where applicable, release of the applied pre-test floor deformation.
(i) Seats. The following post -test deformations and limitations regarding emergency egress and access to exits may be used for showing compliance with § 29.785(j):
(A) Forward or Rearward Directions. The forward or rearward deformations should not exceed a maximum of 4.0 inches (100 mm). In addition, the clearance between undeformed seat rows, measured as shown in Figure AC 29.562-5 (Dimension A), should be a minimum of 9.0 inches, except where seat rows lead to Type III or IV exits, where it should be a minimum of 11.0 inches. For seats with Page C - 83
AC 29-2C, Chg 1 2/12/03 deformations exceeding 4.0 inches, the undeformed clearances between seats should be increased accordingly. In addition, at seat rows leading to Type III or IV exits, a minimum of 20 inches clearance, measured above the arm rests, must be maintained between adjacent seat rows. This measurement may be made with the seat backs returned, using no more than original seat back breakover forces, to their pretest upright or structurally deformed position. At other seat rows, the most forward surface o f the seat back should not deform to a distance greater than one half of the original distance to the forwardmost hard structure on the seat (see Figure 29.562-6).
(B) Downward Direction. There is no limitation on downward deformation, provided it can be demonstrated that the feet or legs of occupants seated aft would not be entrapped. Additionally, the seat bottom rotational deformation from the horizontal, measured at the centerline of each seat pan, should not exceed 20° forward (pitch down) or 35° aft (pitch up). This measurement should be made between the fore and aft extremities of the seat pan structure, considering the final position of the seat pan structure. In no case should rotation of the seat pan cause entrapment of the occupant.
(C) Sideward Direction.
(1) The deformed seat should not encroach more than 1.5 inches (40 mm) into the required space for longitudinal aisle at heights up to 25 inches (635 mm) above the floor. Determine which parts of the seat are at what heights 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.
(D) Additional Considerations. In addition, none of the above deformations 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 except as stated in § 29.813(c)(2).
Page C - 84
Measurement to be taken over full width of seat bottom cushion FIGURE AC 29.562-5 Pre-test condition Post-test condition Dimension “C” must be at least 50% of Dimension “B” FIGURE AC 29.562-6 Page C - 85
AC 29-2C, Chg 1 2/12/03
(2) Encroach into any required passageway to large exits, § 29.813(a) and (b).
(3) Encroach more than 1.5 inches into any cross aisle or evacuation (flight attendant) assist space for certain exits.
(ii) Stowable Seats. Stowable seats, if used, should stow post -test and remain stowed without projecting into any required passageways. In addition, they should not project more than 1.5 inches into any flight attendant assist space or cross-aisle.
(A) Seats that are Stowed Manually. A post -test stowage force no greater than 10 pounds (22kg) above the original stowage force may be used to stow the seat.
(B) Seats that Stow Automatically. For a seat that may interfere with the opening of any exit, it shall automatically retract to a position that does not interfere with the exit opening as prescribed in § 29.807. For determining encroachment into passageways, cross-aisles, and assist spaces, a posttest stowage force no greater than 10 pounds (22kg), applied at a single point, may be used to assist automatic retraction.
e. Test Documentation.
(1) General. The tests discussed in this guidance should be documented in reports describing the test procedures and results. The test proposal, a description of the required tests, approved by the FAA should be referenced in the test report and contain the following:
(i) 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) The date of the last instrumentation system calibration and the name and telephone number of the person responsible for instrumentation system calibration.
(E) A statement confirming that the data collection was done in accordance with the recommendations in this guidance or a detailed description of the actual calibration procedure used and technical analysis showing equivalence to the recommendations of this AC (Paragraph c(2)(iii)(A)).
Page C - 86
(F) Manufacturer, governing specification, serial number, and test weight of ATD used in the tests, and a description of any modifications or repairs performed on the ATD which could cause them to deviate from the specification.
(G) A description of the photographic-instrumentation system used in the tests (Paragraph c(2)(iii)(B)).
(ii) Seat/Restraint system data.
(A) Manufacturers 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.
(B) For unsymmetrical systems, an analysis supporting the selection of most critical conditions used in the tests.
(2) Test Proposal or Plan and Description. The description of the test should be documented in enough detail so that the tests could be reproduced by following the guidance given in the report. The procedures outlined in this guidance can be referenced in the report but should be supplemented, as necessary, to describe the unique conditions of the individual seat design.
(i) Pertinent dimensions and other details of the installation 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.
(ii) The floor deformation procedure, guided by goals of most critical loading for the test articles, should be documented.
(iii) 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, and transducers and data channel characteristics for lap belt loads, floor reaction forces, or other measurements beyond those discussed in this guidance.
(iv) Any unusual or unique activity or event pertinent to conducting the test should be documented. This could include use of special “breakaway” restraints or support for the ATD’s, test items or transducers, operational conditions or activities such as delayed or aborted test procedures, and failures of test fixtures, instrumentation system components or ATD.
(3) Test results report. The documentation should include copies of all test results, analysis, and conclusions. As a minimum, the following should be documented:
Page C - 87
AC 29-2C, Chg 1 2/12/03
(i) Impact pulse shape (Paragraph d(2)).
(ii) HIC results for all ATD exposed to secondary head impact with interior components of the rotorcraft (Paragraph d(3)), or head strike paths and velocities if secondary head impact is likely for future use in unique interiors (Paragraph c.(3)(iii)).
(iii) Impact velocity (Paragraph d(4)).
(iv) Upper torso restraint system load if applicable (Paragraph d(5)).
(v) Compressive load between the pelvis and the lumbar column (Paragraph d(6)6).
(vi) Retention of upper torso restraint straps if applicable (Paragraph d(7)).
(vii) Retention of lap safety belt (Paragraph d(8)).
(viii) Femur thigh loads, optional measurement.
(ix) Seat attachment (Paragraph d(10)).
(x) Seat deformation (Paragraph d(11)).
(xi) Seat attachment reaction time histories (Paragraph f).
(4) Dynamic Impact Test – Pass/Fail Criteria: The dynamic impact tests should demonstrate that:
(i) The seat structure remains intact that is attached to the tracks or fittings, etc.
(ii) The occupant retention system is capable of carrying the dynamic loads.
(iii) The s eat permanent deformations are within defined limits and will not significantly impede an occupant from releasing the torso restraints, standing and exiting the seat.
(iv) If the ATD’s head is exposed to impact during the test, a HIC of 1,000 is not exceeded. Data may be obtained for use with other unique installations.
(v) Where upper torso restraint straps are used, tension loads in individual straps do not exceed 7.78 kN (1,750 lbs.). If dual straps are used for restraining the upper torso, the total strap tension load does not exceed 8.90 kN (2,000 lbs.).
Page C - 88