AC 27-1B, Chg 1 2/12/03 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 § 27.562. The seat deformation is measured subsequent to completion of the dynamic tests and, where applicable, release of the applied pre-test floor deformation.
Seats. The following post-test deformations and limitations regarding emergency egress and access to exits may be used for showing compliance with § 27.785():
(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 27.562-5 (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 - 72
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 of 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 27.562-6).
(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.
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AC 27-1B, Chg 1 2/12/03 Measurement to be taken over full width of seat bottom cushion FIGURE AC 27.562-5 Pre-test condition Post-test condition Dimension "C" must be at least 50% of Dimension "B" FIGURE AC 27.562-6 Page C - 74
(2) Encroach into any required passageway to large exits.
(3) Encroach more than 1.5 inches into any cross aisle or evacuation (flight attendant) assist space for certain exits.
(її) 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 § 27.807. 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)).
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AC 27-1B, Chg 1 2/12/03 (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:
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Impact pulse shape (Paragraph d. (2)).
(i) 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)).
(vi) Retention of upper torso restraint straps if applicable (Paragraph d.(7)).
(vii) Retention of lap safety belt (Paragraph d. (8)).
(vili) 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:
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 seat 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 Page C - 77
AC 27-1B, Chg 1 2/12/03 restraining the upper torso, the total strap tension load does not exceed 8.90kN (2,000 Ibs).
(vi) The maximum compressive load measured between the pelvis and the lumbar column of the (ATD) does not exceed 6.67 kN (1,500 lbs.).
(vii) Each upper torso restraint strap remains on the ATD shoulder during impact.
(viii) The pelvic restraint remains on the ATD pelvis during impact.
Procedures for Evaluating Impact Pulse Shapes.
(1) Acceptable Evaluation Method. Data for evaluating the impact pulse shape are obtained from an accelerometer which measures the acceleration on the test fixture or sled at the seat location or equivalent location in the direction parallel to the line of inertial response shown in Figure 27.562-1 of this guidance. The impact pulses intended for the tests discussed in this guidance have an isosceles triangle shape.
These ideal pulses are considered minimum test conditions. Since the actual acquired test pulses will normally differ from the ideal, it may be necessary to evaluate the acquired test pulses to insure the minimum requirements are satisfied.
(2) An acceptable method to evaluate the pulse shape should use the following steps:
Extend the calibration baseline (zero G)
(ii) Locate the maximum peak deceleration (Gp) indicated on the plot.
(ili) Construct reference lines parallel to the baseline at levels of 0.1 Gp,
0.9 Gp, and 1.0 Gp.
(iv) Construct an onset line through the intersection points of the 0.1 Gp and 0.9 Gp reference lines with the increasing (onset) portion of the data plot. The data plot should not return to zero G between the two points selected.
(v) Locate the intersection points of the onset line with the baseline and with the 1.0 Gp reference line. The interval between these two points, measured along the time axis of the data plot, is considered the rise time (tr) of the test impact pulse.
(vi) The rise time of the test impact pulse should not exceed the value of (tr) given in Figure AC 27.562-1 for each test.
(vii) The area under the data plot curve within the rise time of the test impact pulse, Vra, should represent at least one half of the impact velocity given in Figure AC 27.562-1 for each test. If the value of peak acceleration measured in the test Page C - 78
exceeds the level given in Figure AC 27.562-1 by no more than 10 percent, the pelvis to lumbar spinal column force and the upper torso restraint force measured in the test may be adjusted by multiplying the measured values by the ratio of the peak acceleration given in Figure AC 27.562-1, divided by the measured peak acceleration, if necessary.
(vili) The magnitude of Gp should equal or exceed the minimum G given in Figure AC 27.562-1 for each test.
(x) The area under the data plot curve from the intersection point of the onset line and the zero G baseline and a time not more than twice the appropriate rise time specified in Figure AC 27.562-1, plus 30 percent of the rise time later, should represent at least the impact during the test.
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AC 27-1B, Chg 1 2/12/03 Sled Impact Pulse 0,0 —1 Gp!
9 Gp 100 150 200 250 300 350 Time (Milliseconds) FIGURE AC 27.562-7. Impulse Shape Sled Impact Pulse Ta 0,0 Meal Pulse Vira Tred 50 100 1.50 20.0 250 300 350 Time (Milliseconds) FIGURE AC 27.562-8. Change in Velocity (Va) Page C - 80
AC 27.563 § 27.563 (Amendment 27-11) STRUCTURAL DITCHING PROVISIONS.
a. Explanation. Amendment 27-11 included certification requirements for ditching approvals. The rotorcraft must be able to sustain an emergency landing in water as prescribed by § 27.801(e).
b. Procedures. Refer to paragraph AC 27.801 for procedures.
AC 27.563A § 27.563(Amendment 27-26) STRUCTURAL DITCHING PROVISIONS.
a. Explanation. Amendment 27-26 added specific structural conditions to be considered to support the overall ditching requirements of § 27.801. These conditions are to be applied to rotorcraft for which over-water operations and associated ditching approvals are requested.
(1) The forward speed landing conditions are specified as:
(i) The rotorcraft should contact the most critical wave for probable water conditions, in the likely pitch, roll, and yaw attitudes.
(її) The forward velocity relative to wave surface should be in a range of 0 to 30 knots with a vertical descent rate of not less than 5 FPS relative to the mean water surface.
NOTE: A forward velocity of less than 30 knots may be used for multiengine rotorcraft if it can be demonstrated that the forward velocity selected would not be exceeded in a normal one-engine-out touchdown.
(iii) Rotor lift of not more than two-thirds of the design maximum weight may be used to act through the CG throughout the landing impact.
(2) For floats fixed or deployed before water contact, the auxiliary or emergency float conditions are specified in § 27.563(b)(1). Loads for a fully immersed float should be applied (unless it is shown that full immersion is unlikely). If full immersion is unlikely, loads resulting from restoring moments are specified for sidewind and unsymmetrical rotorcraft landing.
(3) Floats deployed after water contact are normally considered fully immersed during and after full inflation. An exception would be when the inflation interval is long enough that full immersion of the inflated floats does not occur; e.g., deceleration of the rotorcraft during water impact and natural buoyancy of the hull prevent full immersion loads on the fully inflated floats.
b. Procedures.
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(1) The rotorcraft support structure, structure-float attachments, and floats should be substantiated for rational limit and ultimate ditching loads.
(2) The most severe wave heights for which approval is desired are to be considered. A minimum of Sea State 4 condition wave heights should be considered (reference paragraph AC 27.801 (§ 27.801) for a description of Sea State 4 conditions).
(3) The landing structural design consideration should be based on water impact with a rotor lift of not more than two-thirds of the maximum design weight acting through the center of gravity under the following conditions:
(i) Forward velocities of 0 to 30 knots (or a reduced maximum forward velocity if it can be demonstrated that a lower maximum velocity would not be exceeded in a normal one-engine-out landing).
(її) The rotorcraft pitch attitude that would reasonably be expected to occur in service. Autorotation flight tests or one-engine-inoperative flight tests, as applicable, should be used to confirm the attitude selected. This information should be included in the Type Inspection Report.
(III) Likely roll and yaw attitudes.
(iv) Vertical descent velocity of 5 FPS or greater.
(4) Landing load factors and water load distribution may be determined by water drop tests or analysis based on tests.
(5) Auxiliary or emergency float loads should be determined by full immersion or the use of restoring moments required to react upsetting moments caused by sidewind, asymmetrical rotorcraft landing, water wave action, rotorcraft inertia, and probable structure damage and punctures considered under § 27.801. Auxiliary or emergency float loads may be determined by tests or analysis based on tests.
(6) Floats deployed after initial water contact are required to be substantiated by tests or analysis for the specified immersion loads (same as for (5) above and for the specified combined vertical and drag loads).
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SUBPART C - STRENGTH REQUIREMENTS
FATIGUE EVALUATION AC 27.571. § 27.571 (Amendment 27-26) FATIGUE EVALUATION OF FLIGHT STRUCTURE.
a. Explanation. An evaluation is required to assure structural reliability of the rotorcraft in flight. This evaluation may take the form of either tests or analysis. During the certification process, fatigue testing is more effective than analysis alone in identifying and preventing cracking that may occur during service. Analysis used for substantiation should be validated by tests.
(1) Chapter 3 AC 27 MG 11 contains background information and acceptable means of compliance with the requirements. A safe life may be assigned or the structure may be fail safe as prescribed or a combination of these may be used.
(2) Mandatory inspections, service life (replacement times) etc., determined in complying with the standard shall be placed in the Airworthiness Limitations Section of the Instructions for Continued Airworthiness (also called Maintenance Manual). See Appendix A of FAR Part 27, paragraphs A27.4 and paragraph AC 27.1529 for information.
(3) Amendment 27-26 amended the standard to require evaluation of the landing gear and their related primary attachments.
(4) Amendment 27-26 also amended the standard to require evaluation of ground-air-ground cycles on the rotorcraft, and if applicable, of external cargo operations. Previously external cargo operations were evaluated whenever the rotorcraft cargo combination exceeded the "standard" maximum certificated gross weight, and the CG range specified in § 27.25(c). If these limits were not exceeded, an evaluation was not required by the standard prior to Amendment 27-26.
b. Procedures.
(1) The fatigue evaluation requires consideration of the following factors:
(i) Identification of the structure/components to be considered.
(ii) The stress during operating conditions.
(ili) The operating spectrum or frequency of occurrence including frequency of ground-air-ground cycles, as well as external cargo operations.
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