9. Engine Rating and Limits - § 33.7. For all ETOPS eligible models, a TCDS note should be included to indicate eligibility. For models that comply with § 33.201 for Early ETOPS, the note should also describe the demonstrated diversion time. A sample note for each situation is shown below:
“Model xxx has complied with the requirements of §§ 33.4(A33.3(c)), and 33.71(c)(4), and is therefore eligible for installation on Extended Operations (ETOPS) approved airplanes. Note that ETOPS eligibility does not constitute airplane or operational level approvals necessary to conduct ETOPS flights.”
OR
“Model xxx has complied with the requirements of §§ 33.4 (A33.3(c)), 33.71(c)(4) and
33.201, and is therefore eligible for installation on Extended Operations (ETOPS) and Early ETOPS approved airplanes. The demonstrated diversion time is xyz minutes at MCT plus 15 minutes at hold power*. Note that ETOPS eligibility does not constitute airplane or operational level approvals necessary to conduct ETOPS flights.
*Note the hold condition run time if included in the simulated diversion cycles of the § 33.201 endurance test.”
10. Reliability Reporting for Two Engine Airplanes - § 21.4(b).
a. Reporting. Section 21.4(b) applies to both airplane and engine type certificate holders with two-engine ETOPS fleets. Section 21.4(b)(1) requires each type certificate holder to investigate IFSD events and submit a periodic (monthly or quarterly as applicable) ETOPS report for each ETOPS two-engine airplane model type design approved for ETOPS. The report must be transmitted to the cognizant FAA aircraft certification office, and must contain the following information:
(1) IFSD rates (world fleet 12 month rolling averages; engine basic and total installed);
(2) IFSD reports for the period (descriptions/findings); and
(3) ETOPS fleet utilization data (operators, diversions, diversion time authority, hours/cycles as available, etc.).
b. The world fleet IFSD rates include all operations of the ETOPS-approved airplane/engine combination, not just ETOPS flights. The submitted IFSD rate information may combine multiple engine models within a distinct family that are installed on ETOPS airplanes, if concurred with by the FAA. The IFSD reports should include a description of the event and investigation results. Note that reporting under § 21.4 can be combined with § 21.3 reporting, at applicant discretion.
c. Section 21.4(b)(2) defines the 12 month rolling average total IFSD rates required for each level of ETOPS airplane type design approval. These IFSD rates are the same as required under part 25 (appendix K) for airplane ETOPS type design approval. This section also requires the type certificate holder to publish service information that will enable operators to maintain the required airplane/engine combination world fleet IFSD rates. Service information can take the form of Service Bulletins, Service Letters, All Ops Wires, etc., published as necessary.
Francis A. Favara, Manager, Engine and Propeller Directorate Aircraft Certification Service
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APPENDIX A. Equivalent Amplitude Fatigue Exponent Determination
a. Discussion. The Equivalent Amplitude Fatigue Exponent has its origin in the S.S. Manson Method for Universal Slopes (1). Manson demonstrated that the fatigue exponents for many metals could be averaged and used to develop a universal fatigue exponent approximating either the low or high cycle capability of metallic materials. Although Manson used the approach to develop generic fatigue exponents representing a broad range of metals, the approach has been demonstrated to be applicable to characterizing the fatigue exponent for individual materials too
(2)(3). When the fatigue exponent is combined with cumulative damage calculations, it can be used to assess accelerated fatigue tests (4). These various authors suggest the fatigue exponent may range from 4 to 20 depending on material and whether high cycle or low cycle fatigue is being evaluated. These authors also indicate that metallic materials typically exhibit high cycle fatigue exponents in the range of 4-8. The FAA determined that 5.68 is an overall acceptable value covering a variety of currently used turbine engine metals over a range of R-ratios for high cycle fatigue. If an engine design departs significantly from the use of conventional metals, then a reevaluation of the exponent in accordance with the references below may be required.
1. Manson, S.S., “Interfaces Between Fatigue, Creep, and Fracture”, NASA Technical Memorandum, NASA TM X-52189, 1966.
2. Lampman, S.R, et.al, “Fatigue and Fracture” ASM Handbook, Volume 19, 1996.
3. Delgado, I.R., G.R. Halford, B.M. Steinet & C.M. Rimnac, “Strain-Life Assessment of Grainex Mar-M 247 for NASA’s Turbine Seal Test Facility”.
4. Fackler, W.C., “Equivalence Techniques for Vibration Testing”, SMV-9, Shock and Vibration Information Center, US DoD, 1972.
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