Appendix 1 APPENDIX 1. FAILURE MODES AND EFFECTS ASSESSMENT
1. A failure modes and effects assessment is a qualitative process, independent of failure rates and probabilities, by which each failure mode of a part in the engine system is analyzed. Some top-level functions typically considered in an engine failure modes and effects assessment are:
• Maintaining structural integrity, including allowed overspeed and overtemperature exceedances;
• Providing thrust or power;
• Operating in inclement weather;
• Providing customer bleed, power extraction, or both; and
• Meeting fuel consumption, exhaust gas temperature, vibration, emission or noise limits.
2. Each system and subsystem of the engine is broken down into its basic functions using a functional block diagram consistent with the Air Transport Association policy for identification and definition of systems.
3. The functional block diagram defines each system and subsystem, and all their functions, in the turbine engine. The experienced safety engineer performing the analysis determines the partto-part and part-to-system influences in both directions (input and output). The process flow is shown in figure A1.1 below:
Figure A1.1. Process Flow Diagram Determine input functions from other engine systems Identify parts within the system being analyzed Determine functions provided by the part being analyzed Determine consequence of failure to provide the desired function by design intent Categorize part by outcomes in Tables 1 and 2 of this AC Determine outcome on part, engine system, and the engine 13
Appendix 1
4. The part categorization process is built around the fundamental understanding of the part function and its potential effects on physically or functionally mating parts or both. The fundamental premise in the categorization process, and in the physical operation and function of the turbine engine, is system interactions.
a. System interactions are influences a part, or a set of parts, can have on the turbine engine, propulsion system, or aircraft through form, fit, or function. These influences may extend beyond the component being classified, may be direct or indirect, and may develop immediately or over time. Characteristics of these influences include:
(1) Direct influences, which are form and fit. These influences are based on physical contact or interface clearances between adjacent parts.
(2) Indirect influences, which are functional in nature. These influences are not based on physical contact, but may be aerodynamic, thermal, or vibratory.
5. The interactions where the consequence of failure is the furthest from the cause are the most difficult to identify. Many fundamental relationships in part interactions and subsequent system effects exist. Figure A1.2 below provides four examples.
Figure A1.2. Part Interaction Considerations Indirect Effect 1 Stage 1 HPT Effective Nozzle area/flow 2 Indirect Effect Fuel Pump Fuel flow Impeller sch edule Time Relationship3 Stage 2 HPT Cooling flow to Nozzle rotor Direct Effect Loads and Rotor Blade mo ment s on disk HPC press.
ratio Stall margin Stall at limiting consumption condition Fuel to Starting Altitude re-light Combustor characteristic capability Critical part Purge flow Hot gas temperature & level ingestion life Local dovetail Dovetail or slot LLP life impact loading bottom life 14 Part Interaction
Considerations
•Fluid interactions
• Air, fuel, oil
•Direct interactions
• Mechanical loading
• Aero loading
• Contact/wear
• Chemical
•Indirect interactions
• Vibration
• Acoustical
• Primary air
• Secondary air
• Control system
• Structural dynamics
• Sensor systems 4
Appendix 2 APPENDIX 2. TEMPLATES
1. This appendix provides 17 templates, listed in Table A2-1 below. The FAA selected them based on what we found applicants were typically submitting for complex turbine engine part PMA approval. These templates will aid applicants in identifying the technical elements and regulatory requirements they should consider when developing their test and substantiation plans. Applicants must ensure that any additional technical criteria or regulatory requirements are met for their specific proposed PMA part. Each template is subdivided into the following sections:
a. Section 1 - Part functional capability, which is the action the part is designed to perform in the engine.
b. Section 2 - Part shape, size, dimensions, and other physical, measurable parameters;
interconnectivity with an engine integral part or system; or both.
c. Section 3 – Part materials and processes – properties.
d. Section 4 – Part materials and processes – processing.
e. Section 5 - Applicable analyses.
f. Section 6 - Applicable testing.
g. Section 7 - Applicable regulatory requirements.
2. Sections 1 through 5 are divided into the following five columns:
a. Column 1 is the section number.
b. Columns 2 and 3 identify part characteristics to be evaluated to support the functional design intent of the type design part.
c. Column 4 identifies typical areas applicants should evaluate for potential part and system failure modes.
d. Column 5 is used to identify a combination of actions and criteria for risk mitigation and control when a corresponding failure mode is identified in column 4.
3. Section 7 of the templates identifies the part 33 (Amendments 1-20 inclusive) airworthiness requirements applicable to turbine engines. However, not all engine certification bases include the same requirements.
4. If a template is not available for a particular part, the applicant can create or modify another as necessary. For example, although templates specific to APU parts are not provided, the 15
Appendix 2 applicant may use the templates for similar APU parts and revise the regulatory section to reflect the requirements of TSO C77.
Table A2-1. Available Templates Template Number Part Name 1 O-Rings 2 Embedded elastomer seals 3 Combustor 4 Low pressure turbine blade 5 Turbine vane cooled 6 Turbine vane un-cooled 7 Shaft 8 Roller bearing 9 Ball bearing 10 Gear 11 Compressor vane 12 Compressor blade 13 Static air seal 14 Variable stator vane lever arms 15 Bushings 16 Turbine blade cooled 17 Fuel filter 16
Appendix 2 Template #1: O-Rings This template deals with non-standard seals which are typically procured under a TC holder part number. If the part is listed as a standard part and can be procured commercially these requirements do not apply.
Inner Diameter Outer Diameter Width Mold Line/Flash Cross-Section Shape May Vary Nomenclature for Generic Component Features (all features may not be applicable) 17
Appendix 2 Section 1 – Part Functional capability, i.e., the action(s) that the part is designed to perform in the product Section/ Number Characteristic Critical to Part Functionality Key Characteristics Part and System Failure Modes Risk Mitigation and Control 1-1 Static Size • Physical dimension • Dimensionally within limits • Dimensional process control 1-2 Material • Actual material used in part • Base material certifications • Verify certificates 1-3 Temperature limits • Maximum and minimum temperatures • Recommended limits by manufacturer • Verify capability exceeds expected duty cycle 1-4 Chemical resistance • Compatibility with TC holder approved fluids in applicable system.
• Recommended limits by manufacturer • Verify capability exceeds expected duty cycle
• Verify chemical compatibility with TC holder approved fluids.
Section 2 – Part Shape, size, dimensions and other physical measurable parameters, and interconnectivity with an engine integral part/system Section/ Number Characteristic Critical to Part Functionality Key Characteristics Part and System Failure Modes Risk Mitigation and Control 2-1 Boundary dimensions
• Inside diameter
• Outside diameter
• Cross sectional size
• Installation into assembly • Dimensional process control and inspection 2-2 Surface finish • Actual surface conditions • Ability to perform sealing function • Dimensional process control 2-3 Fit-up dimensions • Design compression/expansion
• set/spring back
• Ensure compression is within the allowable range • Dimensional process control and inspection 2-4 Tolerance • Variance-Fluctuations in measurements • Mechanical/Functional, failure due to variation from nominal
• Verify part is tolerant to variation
• Control of manufacturing and inspection processes 18
Appendix 2 Section 3 – Part Materials and Processes – Properties Section/ Number Characteristic Critical to Part Functionality Key Characteristics Part and System Failure Modes Risk Mitigation and Control 3-1 Chemistry • Major elements - % Variation
• Impurities
• Poor mechanical or environmental resistance properties • Material selection
• Process control 3-2 Physical properties • Density
• Coefficient of thermal expansion
• Melting Point
• Consistent properties within operating parameters • Material selection
• Process control 3-3 Mechanical properties
• Modulus
• Hardness/Durometer hardness
• Low material properties • Adequate material properties
• Operational effects accounted for 3-4 Environmental resistance
• Oxidation
• Temperature range
• Corrosion
• Chemical resistance
• Age related material property change
• Physical deterioration from Oxidation/Corrosion/chemical attack
• Property reduction due to extreme temperatures
• Verify adequate environmental properties Section 4 – Part Materials and Processes - Processing Section/Number Characteristic Critical to Part Functionality Key Characteristics Part and System Failure Modes Risk Mitigation and Control 4-1 Raw material processing • Purity • Inadequate material properties • Process control (melt control, cleanliness)
• Process control and sequencing 4-2 Surface treatment • Proper form and texture • Improper thickness and excess flash • Process control 4-3 Process sequencing and Significant Process Identification and Substantiation
• Inspection
• Manufacturing
• Process Substantiation and Control (RSS,RSA,ESA, etc)
• Inadequate final part form, or defect “escape” • Verify adequate control of processes and parameters Section 5 – Analysis Section/Number Characteristic Critical to Part Functionality Key Characteristics Part and System Failure Modes Risk Mitigation and Control 5-1 Operating conditions
• Temperatures
• Sealing ability
• Proper contact pressures
• Inadequate part life due to analysis under-predicting part temperature, mechanical stress, chemical resistance
• Perform analysis at relevant operating conditions 5-2 Variation • Engine operation characteristics • Inadequate part function due to variation • Verify part is tolerant to variation 19
Appendix 2 Section 6 – Testing Section/Number Characteristic Critical to Part Functionality Key Characteristics Part and System Failure Modes Risk Mitigation and Control 6-1 Durability • Engine vibration response
• Leakage
• Excessive leakage
• Excessive Vibration
• Perform adequate component and/or engine testing 6-2 Operability and performance
• Vibration signature
• Abnormal wear
• Environmental testing to hot and cold limitations for the engine. Thermal conditions at the “O” ring seal installed location
• Durability/replacement interval(s)/shelf life, etc, if applicable?
• Excessive leakage
• Difficult to disassemble after operation
• Engine testing Section 7 – Potential Impact on Regulatory Requirements Note: The regulatory requirements identified below, which are inclusive up to Amendment 20 of 14 CFR part 33, are intended as a guide to applicants when determining the applicable regulations to which they must show compliance. Those requirements listed as “Could be affected” highlight the regulations whose compliance findings are typically affected by the component or part that this template is addressing.
This guide is not all-inclusive and the applicant remains responsible for identifying the certification basis of the product on which their PMA part is to be installed.
Applicable 14 CFR Part 33 Regulatory Requirements Comments Subpart A – General
1. 33.4 Instructions for Continued Airworthiness Could be affected ICAs including on-wing inspection requirements and on-wing limits for leakage
2. 33.5 Instruction manual for installing and operating the engine
3. 33.7 Engine ratings and operating limitations
4. 33.8 Selection of engine power and thrust ratings 20
Appendix 2 Subpart B – Design and Construction;
General
5. 33.14 Start-stop cyclic stress (low cycle fatigue)
6. 33.15 Materials Could be affected
7. 33.17 Fire prevention Could be affected No fluid leakage
8. 33.19 Durability Could be affected
9. 33.21 Engine cooling
10. 33.23 Engine mounting attachments and structure
11. 33.25 Accessory attachments
12. 33.27 Turbine, compressor, fan, and turbosupercharger rotors
13. 33.28 Electrical and electronic control systems
14. 33.29 Instrumentation connection Subpart E – Design and Construction;
Turbine Aircraft Engines
15. 33.62 Stress analysis
16. 33.63 Vibration Could be affected
17. 33.65 Surge and stall characteristics
18. 33.66 Bleed air systems
19. 33.67 Fuel system Could be affected Leakage limits
20. 33.68 Induction system icing (Operability aspects)
21. 33.69 Ignition system
22. 33.71 Lubrication system Could be affected Leakage limits
23. 33.72 Hydraulic actuating system Could be affected Leakage limits
24. 33.73 Power or thrust response
25. 33.74 Continued rotation
26. 33.75 Safety analysis 21
Appendix 2 Subpart E – Design and Construction;
Turbine Aircraft Engines
27. 33.76 Bird ingestion (Operability aspects of ingestion)
28. 33.77 Foreign object ingestion (Operability aspects of ingestion)
29. 33.78 Rain and hail ingestion
30. 33.79 Fuel burning thrust augmenter Subpart F – Block Tests; Turbine Aircraft Engines
31. 33.83 Vibration test
32. 33.85 Calibration tests
33. 33.87 Endurance test Could be affected Leakage limits
34. 33.88 Engine over temperature test
35. 33.89 Operation test
36. 33.90 Initial maintenance inspection Could be affected Leakage limits
37. 33.91 Engine component tests
38. 33.92 Rotor locking tests
39. 33.93 Teardown inspection
40. 33.94 Blade containment and rotor unbalance tests (Weight changes)
41. 33.95 Engine-propeller system tests
42. 33.96 Engine tests in auxiliary power unit (APU) mode
43. 33.97 Thrust reversers
44. 33.99 General conduct of block tests
45. Part 33 - Appendix A – Instructions for Continued Airworthiness Could be affected
46. Part 33 - Appendix B - Certification Standard Atmospheric Concentrations of Rain and Hail 22
Appendix 2 Template #2: Embedded Elastomer Seals This template deals with non-standard seals which are typically procured under an OEM part number. If the part is listed as a standard part and can be procured commercially, these requirements do not apply.
Elastomeric Seal (Lip) Puller Feature Seal Diameter Nomenclature for Generic Component Features (all features may not be applicable) 23
Appendix 2 Section 1 – Part Functional capability, i.e., the action(s) that the part is designed to perform in the product Section/ Number Characteristic Critical to Part Functionality Key Characteristics Part and System Failure Modes Risk Mitigation and Control 1-1 Static size • Physical dimension of seal and carrier • Dimensions are within limits • Dimensional process control 1-2 Material • Actual material used in part • Base material certifications • Process control 1-3 Temperature limits • Maximum and minimum temperatures • Recommended limits by manufacturer • Verify capability exceeds expected duty cycle 1-4 Chemical resistance • List of chemicals which the material is compatible with
• Recommended limits by manufacturer • Surface dimensional process control
• Verify acceptable wear
• Verify chemical compatibility with approved engine fluids.
Section 2 – Part Shape, size, dimensions and other physical measurable parameters, and interconnectivity with an engine integral part/system Section/ Number Characteristic Critical to Part Functionality Key Characteristics Part and System Failure Modes Risk Mitigation and Control 2-1 Boundary dimensions
• Hole locations
• Inside contour
• Outside contour
• Cross sectional size of elastomer
• Thickness of carrier
• Installation into assembly • Dimensional process control and inspection 2-2 Surface finish • Actual surface conditions • Ability to perform sealing function • Dimensional process control 2-3 Fit-up dimensions • Design compression/expansion • Ensure compression is within the allowable range • Dimensional process control and inspection 2-4 Tolerance • Variance-fluctuations in measurements
• Parallelism of carrier
• Mechanical/Functional, failure due to variation from nominal
• Verify part is tolerant to variation
• Control of manufacturing and inspection processes 24