Appendix 3. Endurance Test Cycle for Multiple Engine Tests
1. Regulatory basis for multiple engine tests.
a. Section 33.87(a)(3) allows for multiple tests if all the associated limits to the engine operating condition being demonstrated cannot be held at the 100 percent level simultaneously.
If the applicant selects multiple tests to comply with the endurance test requirement, then the applicant must run the additional test(s) in accordance with the prescribed test sequence under §§ 33.87(b) through (g), applicable to all the engine rating conditions (i.e., takeoff, maximum continuous, OEI, and other ratings) being demonstrated. The applicant must run all of these tests on the same engine hardware the applicant presents for certification.
b. For rotorcraft engines for which the applicant desires 30-second OEI and 2-minute OEI ratings, the applicant must repeat the test sequence defined in § 33.87(f) for not less than 120 minutes. If a second test is required to demonstrate all the limits associated with the engine operating condition, then the total test time at the desired OEI conditions should not be less than 240 minutes.
c. Section 33.87(a)(3) also requires that at least 100 percent of the value of all the engine operating parameters associated with a particular engine operating condition must be maintained during the series of runs specified under §§ 33.87(b) through (g), as applicable. If a parameter limit for a particular engine rating (for example, rotor speed for maximum continuous rating) is not defined, then run the test segments associated with that rating condition to the maximum engine redline condition, as defined in the TCDS.
2. Example of multiple engine tests. The following is an example of an acceptable multiple engine test sequence for a turbofan engine in compliance with § 33.87(b). If during the first test, the applicant demonstrates simultaneous core rotor speed limit and the gas temperature limit, the applicant should demonstrate the second test at the fan rotor speed limit and the gas temperature limit, simultaneously, in accordance with the test sequences defined in §§ 33.87(b)(1), (b)(2)(i),
(b)(2)(ii), (b)(3), and (b)(5). This second demonstration would accumulate an additional 87.5 hours of testing at redline fan speed and gas temperature, resulting in a total time of 237.5 hours on the same engine hardware for this endurance test. The applicant may choose to run the test in two parts (on the same set of engine hardware) as provided in paragraphs a. and b. below.
a. Part One. Run a standard 150-hour endurance test in accordance with § 33.87(b) at the redline core rotor speed, the gas temperature limit, and the rated thrust, simultaneously.
(1) During the takeoff parts of the test, the applicant must maintain:
(a) The fan rotor speed at the level associated with producing the test parameters in 2.a.(1)(b), (c), and (d) of this paragraph,
(b) The core rotor speed at or above the takeoff redline limit,
(c) The gas temperature at or above the takeoff redline limits, and A3-1
(d) The thrust at or above the takeoff rating value.
(2) During the maximum continuous parts of the test, the applicant must maintain:
(a) The fan rotor speed at the level associated with producing the test parameters in 2.a.(2)(b), (c), and (d) of this paragraph,
(b) The core rotor speed at the maximum permissible speed associated with the maximum continuous rating. If a maximum permissible rotor speed is not defined for the maximum continuous rating, then the maximum continuous test segments must be run to the rotor speed redline limit usually associated with the takeoff rating,
(c) The gas temperature at or above the rated maximum continuous limit. If a gas temperature limit is not defined for the maximum continuous rating, then the maximum continuous test segments must be run to the maximum gas temperature redline limit usually associated with the takeoff rating, and
(d) The thrust at or above the rated maximum continuous value.
b. Part Two. Re-run only the takeoff and maximum continuous parts of the cycle under the test sequences defined in §§ 33.87(b)(1), (b)(2)(i), (b)(2)(ii), (b)(3), and (b)(5) at fan rotor speed, gas temperature limits, and rated thrust simultaneously. The run time for Part Two is 87.5 hours, which consists of 18.75 hours at takeoff power, 45 hours at maximum continuous, and
23.75 hours at minimum idle.
(1) During the takeoff parts of the test, the applicant must maintain:
(a) The core rotor speed at the level associated with producing the test parameters in 2.b.(1)(b), (c), and (d) of this paragraph,
(b) The fan rotor speed at the takeoff redline limit,
(c) The gas temperature at the takeoff redline limit, and
(d) The thrust at the rated takeoff thrust level.
(2) During the maximum continuous parts of the test, the applicant must maintain:
(a) The core rotor speed at the level associated with producing the test parameters in 2.b.(2)(b), (c), and (d) of this paragraph,
(b) The fan rotor speed at the maximum permissible speed associated with the maximum continuous rating. If a maximum permissible rotor speed is not defined for the maximum continuous rating, then the maximum continuous test segments must be run to the rotor speed redline limit usually associated with the takeoff rating, A3-2
(c) The gas temperature at the maximum continuous redline limit. If a gas temperature limit is not defined for the maximum continuous rating, then the maximum continuous test segments must be run to the maximum gas temperature redline limit usually associated with the takeoff rating, and
(d) The thrust at the maximum continuous rating level.
c. The total run time for the multiple endurance test runs, including Part One and Part Two is 237.5 hours, i.e., 150 hours and 87.5 hours.
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Appendix 4. Engine Configuration Modifications in Endurance Test
1. To run the endurance test at redline conditions simultaneously, i.e., at maximum permissible rotor speeds, gas temperature, and full rated thrust or torque as required by § 33.87(a)(3), the applicant may need to modify the engine configuration or use certain additional facility test equipment. The applicant should include the modifications to the engine configurations and additional facility test equipment in the test plan. See appendix 2, paragraphs 2.b. and 2.c. The following methods are commonly used to match engine speeds and temperatures to achieve the desired test conditions.
a. Change the inlet airflow and condition by:
(1) Changing the inlet nozzle area,
(2) Installing an inlet grid or screen to introduce a pressure drop at the inlet, or
(3) Heating the inlet air.
b. Variable compressor stator vane mis-scheduling.
c. Use of customer bleed from high-pressure compressor or low-pressure compressor, or both.
d. Use of a variable area hot section nozzle.
e. Use of a variable area exhaust nozzle.
2. When one or more of the above methods is chosen, the applicant should provide a technical justification that shows that the tested configuration does not compromise test requirements under § 33.87 or mask stability issues.
3. Operating the engine at triple redline conditions requires some nonstandard adjustments to the engine’s designed control and operating characteristics. These adjustments may result in unintended adverse consequences to some engine design features.
a. For example, attaining redline core rotor speeds simultaneously with redline gas temperatures may require off-design point scheduling of the compressor variable stator vanes and other engine hardware. This in turn may reduce the amount of air that can be bled internally from the compressor for pressurization of bearing sump areas and for cooling various high- and low-pressure turbine components. Section 33.87 does not require that the engine be tested with an engine system, such as these cooling circuits, reduced in capability or effectiveness below the design intent level at which it would operate if the engine remained in a type design configuration.
b. The applicant may propose minor modifications to the engine to mitigate these unintended consequences. For example, the applicant may propose restoring the type design A4-1
cooling by modifying the compressor internal cooling flow circuit and increase the flow regulating orifice diameters.
c. For each proposed modification, the applicant should show in the test plan that the modification doesn’t enhance the capability to withstand the rigors of the intended test conditions for that modified part or for any other part affected by the modified part. For example, for the modification discussed in paragraph b. of this appendix, the applicant should show that:
(1) The modifications to the compressor cooling flow circuit do not improve the capability of the compressor case to withstand the test conditions, and
(2) The increased cooling flow does not improve the capability to withstand the rigors of the test for the hot section parts that are pressurized or cooled by this flow. The reconciliation for any such modified parts (i.e. non-type design) should be included in the reconciliation section of the test plan.
d. The modifications to the test engine configuration should still allow the engine to substantially conform to the final type design. In addition, the test engine, as modified, should be representative of the durability and capability of a typical type design engine to withstand the rigors of the test.
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Appendix 5. Endurance Test Conformity Inspections and Type Inspection Authorization
1. The calibration and endurance test engine(s) must substantially conform to the final type design configuration, except for non-type design hardware approved by us. The applicant should make all inspections necessary to determine that the parts and components of the engine adequately conform to the drawings and specifications of the type design, and the engine is built to the assembly procedures specified in the type design. Our manufacturing inspectors or an FAA designee will conduct pre- and post- test conformity inspections. The applicant should also disclose any deviations (referred to as “nonconformances”) of hardware, software, and components from the type design, and should provide acceptable evidence that these non-type design characteristics will not adversely affect the outcome or the integrity of the test. Finally, the applicant should report the data generated in pretest conformity inspections to us for our review. For reporting, the applicant should use the applicable reporting format. Refer to FAA Order 8110.4C for the type certification procedures related to conformity inspections.
2. Certain test hardware should be subject to preassembly conformity inspections by either our manufacturing inspector or the FAA-designated inspector. The inspectors should give particular attention to critical characteristics of critical and major parts that are subject to significant temperatures, distortion, cracking, fatigue, creep, and wear. This conformity inspection may vary, depending upon circumstances, and is based on a conformity inspection plan. Our pretest review of applicant's quality control procedures, inspection personnel experience, and inspection facilities capability will help to determine the extent of the required conformity inspections prior to the endurance test. Refer to FAA Order 8110.4C for conformity inspection requirements.
3. The type inspection authorization (TIA) is normally prepared by our certifying office upon the applicant’s request, and is used to authorize conformity inspections to ensure that the test engine hardware conforms to the approved type design for certification. The TIA should identify the test engine configuration, including germane hardware for the test, the FAA-approved nontype design hardware, and the parts that are subject to preassembly inspection. We may also issue a TIA requiring special inspections on either the test engine or the test facilities when we find it necessary. For more information on the request for conformity inspection, TIA, statement of conformity, type inspection report, and related instructions, see chapter 5 of FAA Order 8110.4C, Type Certification.
4. The following example shows hardware that is germane to a demonstration under § 33.87 required by a redesigned annular combustor. Assume the combustor redesign alters the actual discharge gas temperature profile relative to the gas temperature measured by the turbine temperature assembly. This factor then changes the operating envir onment of all parts that are affected by a change in the gas temperature characteristics. The objective of the endurance test is to demonstrate that the core engine hardware affected by changes to the gas path environment will satisfactorily pass a 150-hour endurance test at the maximum permissible gas temperature.
In this example, the germane hardware is the:
a. Diffuser case,
b. Combustor section, which includes:
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(1) Fuel nozzles;
(2) Inner and outer liners, inner and outer cowls, and domes;
(3) Inner and outer support rings; and
(4) Combustion case.
c. High-pressure turbine (HPT) section, which includes:
(1) Disks, vanes, blades, and side plates;
(2) Air seals and shrouds;
(3) Inner and outer supports, and outer case; and
(4) Cooling air manifold.
d. HPT to low-pressure turbine (LPT) transition duct,
e. LPT section, which includes:
(1) Disks, blades, and vanes;
(2) Air seals and shrouds; and
(3) Inner and outer supports, and outer case.
f. Exhaust section, which includes:
(1) Turbine exhaust case,
(2) Tailpipe, and
(3) Gas temperature probe assembly.
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Appendix 6. Test Reports Requirements
1. The certification test reports should contain sufficient data (for example, plots, tabulations, figures, and photographs) and discussions to show that the engine successfully completed all requirements of the calibration test, endurance test, and teardown inspection. In addition to test results and data analyses, the applicant should include analyses of engine faults, significant hardware deterioration, and corrective actions.
2. The following paragraphs describe types of data, analysis, and other information that applicants should include in reports for the calibration test, endurance test, and teardown inspection. The information categories are for use as a guide in preparing the reports and are not all-inclusive or mandatory.
a. Objective. List the part 33 paragraphs for which the test results are intended to show compliance.
b. Success Criteria. Describe the criteria for determining if the engine performance characteristics and the condition of parts and components meet the requirements of §§ 33.85 and
33.93, respectively.
c. Engine and facility configuration. Include descriptions of the engine build, facility hardware, and special test facility hardware required, e.g., to accommodate compressor bleed air extraction or to achieve maximum oil temperature.
d. Modifications. Include redline target value changes and hardware changes that are different from the bill of materials contained in the TIA. Disclose any changes to the germane or principal hardware and show that these changes will not affect the outcome of the test and that the changed parts are still representative of the type design part.
e. Test discussions. Include results from these test areas:
(1) Pre-endurance testing. Include discussions of the results of pre-endurance engine and component test calibrations that were used to establish the baseline operating characteristics of the engine.
(2) Endurance testing. Discussions should include, but are not limited to:
(a) Descriptions of any deviations from the prescribed cycle requirements. The applicant must show that these modified cycles are still in compliance with the regulation.
(b) Descriptions of any penalty runs that were required to make up for cycles that deviated from the regulation requirements.
(c) Comparative tabulations (versus the § 33.87 requirements) of:
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1 The operating time accumulated at each power condition, including any shortfalls in the gas temperature due to the stabilization exception allowance provided under § 33.87(a)(7).
2 The minimum certificated parameter values obtained during each of the cycle segments showing that the lowest of these minimum segment values was still at or above the value to be certificated.
3 A trace of one “typical” non-bleed cycle segment under § 33.87(b)(1) and one segment (first 5 minutes only) under § 33.87(b)(5), showing stabilization at or above the required values to be certificated prior to starting the timer for each part. This trace will also show the stabilization time for the gas temperature if the stabilization exception provided under § 33.87(a)(7) is used.
(d) Validation that any shortfall between a reduced thrust level that can be achieved and the required minimum physical thrust is inconsequential to the demonstration of durability of those engine parts that are subject to thrust loads.
(3) Post-endurance testing. Include the results of the post-endurance calibration and vibration survey. The vibration survey should show that vibration levels did not significantly change over the duration of the endurance test and are still at or below the allowable limits established for compliance with part 33 requirements. The performance calibration test must show that the engine is still capable of producing its rated power or thrust without exceeding any of the operating limits prescribed in the TCDS.
f. Post-test. Following completion of the endurance test, the applicant must disassemble the engine into modules, subassemblies, or parts as appropriate for a dirty inspection. After completion of the dirty inspection, the applicant should disassemble, clean, and inspect the hardware. The applicant should tabulate any significant inspection findings of engine parts with the part name, part number, inspection results, known or suspected causes, effects on the operation of the engine, and proposed corrective actions or proposed product improvements. If any component fails the acceptance test procedure (ATP), the applicant should describe any the cause and corrective action, and include a summary of the ATP results in the test report. Also, in the test report, identify any engine manual or return-to-service limits affected by the post-test hardware condition, and justify any changes made to these manual limits.
g. Data reporting.
(1) The applicant should present test data in either tabular or graphic formats, and in sufficient detail to show compliance with the test requirements. For example, tables or plots may include typical gas temperature, rotor speed, thrust or power versus time or power setting parameter, oil temperature versus rotor speed, or vibration versus rotor speed.
(2) Include photographs showing significant hardware findings from the pretest and post-test inspections in the test report.
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h. Analysis.
(1) Performance data. Analyze the performance deterioration based on pre- and postendurance calibrations and determine its acceptability for continued operation. The calibration test data must show that following completion of the endurance test, the engine can produce its rated power or thrust without exceeding any speed, gas temperature, or other operating limits in the TCDS.
(2) Bleed air test results. Describe the maximum air bleed amount tested and its effect on temperature, speed, and thrust or power.
(3) Fault and maintenance messages. The applicant should analyze any component that has an indicated maintenance message recorded during the endurance test. The applicant should also include the messages, cause, comments, and corrective action(s) in the report.
(4) Critical dimensions. The applicant should identify the critical dimensions to assess rotor hardware residual plastic growth or deformation. We recommend that applicants include data on critical dimensions, new part dimensions, manual limits, pre- and post-test dimensions, and predicted growth.
(5) Oil pressure and temperature test results. The endurance test must demonstrate that the engine operation with the oil at or beyond the minimum and maximum pressure limits is satisfactory. The test should also show that satisfactory engine operation with the oil temperature at or exceeding both steady-state and transient maximum temperature limits has been successfully demonstrated.
(6) Fluid properties verification. The endurance test report should contain a statement from the applicant that all fluids used during the endurance testing conformed in all respects to the fluid specifications that will be prescribed in the TCDS. Any fluid property differences from the specifications that will be prescribed in the TCDS, including the use of any additives, must be disclosed and justified. Disclose these test results that verify fluid properties in the report.
(7) Vibration signature analysis. The applicant should analyze the vibrations induced by unbalances in both the high and low speed rotor systems, and assure that the vibration level associated with a deteriorated engine is acceptable. The post-endurance test vibration level should remain at or below the allowable limits that were established for compliance with part 33 requirements.
i. Test plan. The final report must include a copy of the approved test plan with the approval documents attached.
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Appendix 7. Endurance Testing for a Two-Minute Transient Overtemperature Limit
Approval
1. Explanation.
a. Two-minute gas transient overtemperature approval for engine acceleration (see § 33.87(a)(3)). We previously approved a 2-minute gas transient overtemperature limit for engine acceleration within the 5-minute time limit associated with the thrust or power rating for turbofan engines under § 33.7. This 2-minute approval addresses a condition in which a gas temperature overshoot occurs subsequent to a large temperature excursion that causes a difference in the thermal growth rate of the engine cases and rotors and a decrease in engine cycle efficiency. This condition occurs most often when an engine is accelerated to takeoff from a cold state.
(1) For turbine engines installed on rotorcraft, the temperature excursion could be significant because rotorcraft flight operations often accelerate the engine from a cold state.
(2) For turbine engines installed on large fixed-wing aircraft, we would not expect such temperature excursions to occur regularly during takeoff operation, due to the time spent from engine start, through push back from the gate and taxi, to takeoff. The following are examples of flight conditions when the temperature overshoot may occur and the gas transient overtemperature limit could be used:
(a) Engine acceleration during first takeoff of the day.
(b) Engine acceleration from a cold soak low power condition.
(c) Engine acceleration from low Mach number during hot day conditions, such as certain corner points of the flight envelope or aircraft go-around operations.
b. Within the 5-minute maximum steady-state gas temperature limit for the takeoff thrust or power rating, the applicant may propose a gas transient overtemperature time limit greater than 30 seconds and less than or equal to 2 minutes. In reviewing § 33.87(a)(3), we determined that the phrase, “must be at least 100 percent of the value associated with the particular engine operation being tested,” may be applied to cover the proposed gas transient overtemperature.
However, since the transient overtemperature is part of the 5-minute steady-state temperature limit, a deteriorated engine should be removed from an aircraft for maintenance whenever the engine fails to produce rated takeoff thrust or power for either the transient overtemperature or the 5-minute steady-state temperature limits, or both.
2. Guidance.
a. For approval of gas transient overtemperature limits greater than 30 seconds and less than or equal to 2 minutes under § 33.87(a)(3), the applicant must demonstrate the proposed limit value and duration for all test periods at takeoff thrust or power condition in § 33.87. This should include the running time of all 30-second periods at takeoff power or thrust in § 33.87, A7-1
unless the exception allowance for gas temperature and oil inlet temperature under § 33.87(a)(7) applies. Section 33.87(a)(7) requires test runs at limiting temperature for any rated power or thrust, except where the test periods are not longer than 5 minutes and do not allow stabilization.
For example, if an applicant proposes a 2-minute gas transient overtemperature limit as part of the 5-minute rated takeoff maximum permissible temperature limit, the following apply:
(1) For the test run under § 33.87(b), the applicant should demonstrate 6 hours and 35 minutes out of the 18.75 hours of running time required by §§ 33.87(b)(1), (b)(2)(ii), and (b)(5), at the 2-minute transient overtemperature limit. We might waive the demonstration required by § 33.87(b)(5) for 30-second periods at takeoff thrust or power if the exclusion provision in § 33.87(a)(7) is applicable.
(2) The TCDS would then specify a 2-minute transient overtemperature out of a 5 minute maximum permissible gas temperature limit for the takeoff rating as follows:
(a) Maximum permissible gas temperature limit for takeoff (5 minutes).
(b) Maximum permissible gas temperature limit for takeoff (2-minute transient overtemperature out of a total of 5 minutes).
(c) A note that indicates that the engine must produce rated takeoff thrust or power within both, the 2-minute transient overtemperature and the 5-minute steady-state redline temperature limits, or it should be removed from service for maintenance.
(3) For approval of the 2-minute gas transient overtemperature limit, the applicant must also comply with the test requirements of §§ 33.27 and 33.88 using the 2-minute gas transient overtemperature value as the maximum steady-state operating temperature limit.
(4) For approval of a gas transient overtemperature limit that exceeds 2 minutes, the applicant must demonstrate the transient overtemperature value for the entire 18.75 hours of running time at takeoff thrust or power.
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