AC 33.70-5
4.1.9 Establishing Interval Limits with Soft-Time Inspection.
When invoked, the soft-time inspection approach establishes interval limits beyond which rotor components must be inspected when the rotors are available in modular form. The soft-time inspection requirement is not intended to affect the current practice of forced inspection programs to address safety of flight concerns that arise in the course of engine operation and maturation. These safety of flight concerns should continue to be addressed through aggressive inspection programs, which are communicated using service bulletins and Airworthiness Directives.
4.1.10 Communication and Implementation of Inspection Assumptions.
4.1.10.1 Applicants should recognize that the inspection assumptions made in the probabilistic risk assessment must be communicated to and implemented accurately in the field by using the ALS of the ICA. These assumptions must also be validated by the review of engine removal rates and module and piece part availability data. For example, the ALS must specify an eddy current inspection if that was an assumption in setting the original soft-time interval.
4.1.10.2 Similarly, the amount of inspected material should correspond to the analysis assumptions. Likewise, if field experience suggests that the opportunity inspection intervals are in excess of the assumed rates in the probabilistic risk assessment, then appropriate corrective action, such as a modified inspection plan, is required.
4.1.11 The soft-time inspection interval and reference to the corresponding inspection procedures must be specified in the ALS of the ICA. This information must be provided for all rotor parts with specified retirement life limits that require any inspection plans beyond opportunity inspections to meet the DTR levels. The required inspection information should also be included in the individual ALS of the ICA with the other rotor inspection requirements. The manufacturer must also provide the necessary information to focus the prescribed inspections to those areas of highest relative risk.
4.1.12 Non-destructive inspection(s) at manufacture cannot be accounted for in the analysis to lower the probability of failure/fracture (POF) value before the application of manufacturing credits (see restriction 5 in appendix F).
4.2 Inspection Scenarios.
The following scenarios clarify the actions that should be taken during a maintenance inspection opportunity (see appendix H.13). Note that the inspection plans may vary for each component based on the outcome of the probabilistic assessments.
4.2.1 Maintenance Opportunity - Hardware Available for Opportunity Inspection.
Hardware available in the condition to perform a specified opportunity inspection must be inspected according to the procedures specified in the ALS of the ICA. This inspection is mandatory.
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AC 33.70-5
4.2.2 Maintenance Opportunity - Module Below Soft Time Interval.
Hardware accessible in the assembled or partially disassembled module may be nondestructively inspected by the procedures specified in the ALS of the ICA. The CSLI may be reset to zero, provided the engine manufacturer has assessed the risk impact associated with this action. This is a discretionary inspection.
4.2.3 Maintenance Opportunity - Module Exceeding Soft Time Interval.
Hardware listed in the ALS of the ICA must undergo nondestructive inspection whenever the module is accessible, particularly when the CSLI for any hardware exceeds the inspection cycle limit. This inspection is mandatory.
4.2.4 Soft Time Inspection Interval Example.
An example of how to develop a soft time inspection interval is provided in chapter 5 of AC 33.70-3.
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AC 33.70-5 APPENDIX A. MA NUFACTURING-INDUCED ANOMALY CALIBRATION TEST CASE FOR
AXIAL BLADE SLOTS A.1 Introduction.
A.1.1 Purpose of the Test Case.
This appendix provides instructions for calibrating a probabilistic risk assessment methodology for manufacturing-induced anomalies in axial blade attachment slots. This includes damage associated with blade insertion and removal during assembly and overhaul. It does not specifically include damage in terms of size or frequency unique to the service operation of the engine.
A.1.2 Scope of Input Data.
This appendix includes all the input data required to complete the test case, such as analysis guidelines, component geometry, boundary conditions, material property data, and inspection efficacy. The input data should be used to compute the POF of a feature within the defined cyclic life interval. An applicant must demonstrate the acceptability of their probabilistic process by meeting the POF criteria defined in table A-8.
A–1
AC 33.70-5 A.2 Test Case Input Data.
A.2.1 Problem Description and Geometry.
The test case geometry, shown in figure A-1, consists of two components: a turbine disk and a blade. Both parts are made from a nickel-based superalloy, with the blade assumed to be solid and isotropic. The blade applies centripetal forces to the disk, but no aerodynamic or pressure loads are applied. In the finite element analysis, the blade should be constrained to prevent axial movement out of the attachment slot.
Figure A-1. Representation of Test Case Blade and Disk Geometry A–2
Figure A-2. Test Case Geometry Definition: Isometric View of 5 Degree Sector Showing Disk and Blade AC 33.70-5 A.2.2 Test Case G eometry Details.
An isometric view and drawings of the disk and blade are shown in figures A-2 through A-8. Dimensions are provided in both Imperial and International System of Units (SI units). The disk features a two-lobe firtree, with 72 equally spaced slots.
A.2.2.1 Figure A-2 provides an isometric view of a 5-degree sector of the test case geometry, showing the disk and blade for the component under assessment.
A–3
AC 33.70-5 A.2.2.2 Figure A-3 provides an axisymmetric profile view of the disk, with dimensions specified in both inches and millimeters.
1.000 -(25.40) 51*22 - 72 SLOTS EQ SP
- 93) ฿18.000
(457.20) @16.300 _R .250
(414.02) (6.34)
•0"13'9" 305
(7.75) ฿12.055
(306.20) . 250
(6.35 ) R 2.000 (50,80) ฿5.994
(152.25) #3.996
1.500 (101.50)
(38.10)
ALL DIM APPLY BOTH SIDES UOS Figure A-3. Test Case Geometry Definition: Disk Axisymmetric Profile in Inches and (Millimeters) A-4
AC 33.70-5 A.2.2.3 Figure A-4 shows a radially inward view of the test case geometry, highlighting an 8-degree broach angle. This view provides critical details of the angular orientation, ensuring a precise understanding of the broaching direction for axial blade slot geometry shown in figure A-5.
Figure A-4. Test Case Geometry Definition: View Looking Radially Inward Showing 8.0 Degree Broach Angle A–5
AC 33.70-5 A.2.2.4 Figure A-5 presents the A -A view of the disk broach slot profile, displaying key dimensions in inches and millimeters.
Figure A-5. Test Case Geometry Definition: View A-A of Disk Broach Slot Profile in Inches and (Millimeters) Not to Scale A–6
AC 33.70-5 A.2.2.5 Figure A-6 illustrates the axisymmetric view of the blade, providing key height and width dimensions in inches and millimeters.
Figure A-6. Test Case Geometry Definition: Axisymmetric View of Blade Showing Height and Width in Inches and (Millimeters) A–7
AC 33.70-5 A.2.2.6 Figure A-7 provides a radially inward view of the blade, illustrating the broach angle and blade thickness in inches and millimeters.
Figure A-7. Test Case Geometry Definition: View of Blade Looking Radially Inward Showing Broach Angle and Blade Thickness in Inches and (Millimeters) A–8
AC 33.70-5 A.2.2.7 Figure A-8 displays the blade attachment profile (View B -B), illustrating the dimensions in both inches and millimeters.
Figure A-8. Test Case Geometry Definition: View B-B Showing Blade Attachment Profile in Inches and (Millimeters) Not to Scale A–9
AC 33.70-5 A.2.3 Mission Profile Definition.
The stresses and corresponding life capability at the disk's slot bottom are primarily driven by the disk's rotational speed but also from the rotor thermal gradient. This test case simulates multiple phases of a typical commercial revenue service operation, capturing changes in disk rotational speed and rotor stress due to thermal contributions through the mission profile. The mission profile is defined by 11 unique time points. A time and disk speed history profile defining these mission points is shown in figure A-9 and table A-1.
Test Case Mission Speed Profile Test Case Mission Temperature Profile 14000 1200 1100 • 600 12000 1000 - 550 900 - 500 Temperature (deg F) 800 - 450 8000 700 Disk Spee 6000 400 4000 300 2000 200 •Disk Slot Bottom 100 *Disk Bore 2000 4000 6000 8000 10000 12000 14000 1600 5000 10000 15000 Mission Time (sec) Mission Time (sec) Figure A-9. Disk Speed and Temperature over Test Case Flight Profile Table A-1. Tabulated Disk Speeds and Temperatures for Test Case Flight Profile Disk Bore Disk Slot Bottom Disk Bore Disk Slot Bottom Rotational Time Temperature Temperature Temperature Temperature Speed Radius = 2.0 in Radius = 8.38 in Radius = 50.8 mm Radius = 212.77 mm sec deg F deg F deg C deg C RPM
42.8 42.8 6.0 6.0 0.0 18 42.8 42.8 6.0 6.0 2708.8 60 64.4 120.2 18.0 49.0 9029.5 608 73.4 208.2 23.0 97.9 9211.1 642 446.0 1,112.0 230.0 600.0 9504.1 1689 975.2 1,050.8 524.0 566.0 12512.6 2008 1,014.8 987.8 546.0 531.0 12182.3 4127 807.8 892.2 431.0 477.9 12158.6 14127 807.8 892.2 431.0 477.9 12046.4 14517 807.8 426.7 431.0 219.3 12042.0 15947 334.4 392.0 168.0 200.0 0.0 A-10