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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AC 27-1B, Chg 3 9/30/2008
(iv) Fatigue strength, and/or fatigue crack propagation characteristics, residual strength of the cracked structure.
(2) Since the design limits, e.g., rotor RPM (maximum and minimum), airspeed, and blade angles (thrust, weight, etc.) affect the fatigue life of the rotor system, it is necessary that flight conditions be conducted at limits that are appropriate for the particular rotorcraft and at the correct combination of these limits. It will be the responsibility of engineering and flight test personnel to determine that the flight strain program proposal includes conditions of flight at the various combinations of rotor RPM, airspeed, thrust, etc., that will be representative of the limits used in service. The flight test personnel should assure that the severity of the maneuvers to be investigated is such that actual service use will not be more severe. Verification that proposed maneuvers are suitable may be achieved by:
(i) Flying a representative set of maneuvers with the applicant's pilot in the test aircraft at noncritical combinations of weight, CG, and speed. (An FAA/AUTHORITY letter for specific test authorization would ordinarily be required.) If the procedure is used, the applicant should provide adequate preliminary flight strain data from development or other tests to confirm a cleared (non-critical) flight envelope for conduct of these representative maneuvers.
Flying a representative set of maneuvers with the applicant's pilot in a similar (certified) model to assess and agree upon the required maneuvers, control deflections, and aircraft rates. The required maneuvers or conditions will be specified in the flight strain program plan.
(iii) Flying a chase aircraft which has a flight envelope appropriate to allow visual confirmation of the proposed and programmed flight maneuvers.
(TV) Observation of telemetered flight data to assure desired control deflections, rates, and aircraft attitudes.
(v) Some combinations of items b(2)(i) through b(2)(iv) above.
(3) Assessing the operation spectrum and the flight loads or strain measurement program will involve airframe, propulsion, and flight test personnel.
(4) Variation in the operating or loading spectrum among models, and variations in the spectrum for a particular model rotorcraft, should be evaluated.
Figure AC 27 MG 11-7 contains typical flight load measurement program conditions to be investigated. An example of a twin turbine spectrum is presented in Figure AC 27 MG 11-9. The tables should be used only as a guide and should be modified as necessary for each particular rotorcraft design.
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(5) The difference in loading spectrum for different models that may be anticipated is illustrated by comparing the percentage of time assigned to level flight conditions, specifically 0.8 V to 1.0 Vu for three different rotorcraft designs as shown in figure AC 27.571-1. (V is the maximum airspeed at maximum continuous power in level flight.) The first column applies to a single-piston-engine powered small rotorcraft used in utility operations. The second column is appropriate for a single-turbine-engine powered seven-place small business and utility rotorcraft. The third column is appropriate for a twin-engine-powered 13 passenger transport rotorcraft. It should be noted that the level flight percentage of occurrences shown in figure AC 27.571-1 for the turbine utility business and turbine transport rotorcraft are examples of particular designs. The high percentage of time shown in this level flight regime could be unconservative for some designs, especially if the stresses under these design conditions produce an infinite fatigue life for the particular component. The fatigue spectrum percentage of occurrences should be modified according to the intended operation usage of the rotorcraft. However, a conservative application should be considered. This variation illustrates the "tailoring" of the loading spectrum for the type of rotorcraft and the anticipated usage.
FIGURE AC 27.571-1 Comparison Percent of Time in Level Flight Turbine Piston Utility Twin Turbine Utility Business Transport
0.8 VNE 25% 0.8 VH 16% 0.8 VH 15%
1.0 VH 15% 0.9 VH 21% 0.9 VH 20%
1.0 VNE 3% 1.0 VH 24% 1.0 VH 38% Total 43% 61% 73%
(6) External cargo operations are a unique and demanding operation. A "logging" operator may use 50 maximum power applications per flight hour to move logs from a cutting site to a hauling site. Power is used to accelerate, decelerate, or hover prior to load release. Lifting loads over an obstruction or natural barrier is another example of very frequent high power applications for takeoff and for hovering over the release area. Similar types of operations require flight loads data to assess the effects on fatigue critical components.
(7) The impact of the external cargo operation on standard configuration limits should be assessed to determine whether or not the component service lives, inspections, etc., will be affected. The assessment may be done by calculating an "external cargo configuration" service life for each critical component. The lowest Page C - 85