and contemplated use of the engine. The applicant must conduct the prescribed 6-hour endurance test cycle 25 times to complete the required 150 hours of operation, unless we approve a different test sequence. For engines seeking the 30-second OEI and 2-minute OEI ratings, the applicant must conduct an additional 2-hour test in accordance with the test schedule in § 33.87(f), for a total test time of at least 152 hours. Appendix 1 of this AC presents the graphical profiles of the endurance test schedules specified in §§ 33.87(b), (c), (d), (e), and (f).
(5) The limits of rotor speed, power or thrust, output torque, and gas temperature that are included in the engine TCDS, as required by § 33.7, must be less than or equal to those values that were demonstrated during the endurance test for each engine rating condition.
b. Endurance test plan requirements.
(1) Applicants should prepare a test plan for the endurance test defining the manner in which the test will be conducted. Applicants should submit this test plan early enough to allow us the time to review and approve the plan prior to the start of the test. At a minimum, the plan should contain:
(a) The applicable part 33 section(s),
(b) A description of the germane or primary hardware to be tested and certified,
(c) A description of properly calibrated test equipment necessary to conduct the test,
(d) Conformity requirements of the test item(s) and test setup,
(e) The test procedure with sufficient detail to fully describe the method of compliance, and
(f) The pass/fail criteria.
(2) See appendix 2 of this AC for additional information about test plan requirements.
c. Test engine configuration.
(1) The test engine configuration must substantially conform to the final type design.
This means that all engine hardware, software, and systems to be certified should have, at most, only minor deviations from the type design. The applicant should disclose, in the test plan, any deviations (referred to as “nonconformances”) of the hardware, software, and components from the type design. The applicant should provide acceptable evidence that these non-type design parts are representative of the capabilities, durability, and operating characteristics of the type design parts, and they will not adversely affect the outcome or the integrity of the test. Further, the non-type design part should not adversely affect the functioning of any other part or system.
Justification of nonconformance acceptability is frequently referred to as reconciliation.
Applicants should submit all such non-type design configuration deviations and associated reconciliations to us for approval.
(a) The standard type design configuration and operating characteristics of some turbine engines may preclude achieving a triple redline test for compliance with § 33.87(a)(3).
Modification of certain test equipment, engine configurations, and test sequences may be necessary to run the test at triple redline conditions. The applicant should show through analysis that the test engine, with any modifications, still represents the durability and operating characteristics of a typical type design engine, and that the engine is capable of complying with § 33.87 requirements.
(b) The applicant may run more than one test on the same set of hardware to be presented for certification if all operating parameters cannot be held simultaneously at 100 percent of the values to be certificated. See appendix 3 of this AC for additional information on an acceptable endurance test cycle for multiple engine tests.
(2) Appendix 4 of this AC shows methods that may be used for matching engine speeds and temperatures for the desired test conditions.
(3) Appendix 5 of this AC provides guidance for the endurance test engine conformity inspections.
(4) The applicant should provide information on aircraft components that will be mounted on or driven by the engine, and that are not part of engine type design. These components may affect the operation of the engine and thus the outcome of the endurance test.
An example of this type of information is the weight, overhung moment, or power extraction loads imposed on the engine by each accessory. The applicant may install the component or simulating loading device on the test engine when approved by us.
(5) Some engine components, such as large integrated starter generators, may require high levels of horsepower extraction from the engine core rotor through the gearbox. High levels of power extraction from the engine core could stall the engine at flight idle or below, or during transient operations. To determine the level of horsepower extraction appropriate for the various segments of the endurance test, the applicant should consider:
(a) The effects of high levels of horsepower extraction on engine stability, operating characteristics, and durability of the power extraction hardware, and
(b) The effects of electrical load transients at critical engine operating conditions, including idle.
d. Engine component and test equipment calibrations.
(1) Before and after the endurance test, the applicant should establish and record the adjustment setting and functioning characteristic of each engine component that can be adjusted independently of installation on the engine, as required by §§ 33.82 and 33.93(a)(1), 7
respectively. These components may include, but are not limited to, the control system, pumps, actuators, heat exchangers, and valves. During the endurance test, all components should operate in a manner consistent with both the type design and the engine operating instructions.
(2) The fuel, lubricating oil, and hydraulic fluid used for the endurance test must conform to the specifications prescribed in the TCDS and ICA. The applicant should provide a statement in the test report identifying the specifications of all engine fluids used during the test.
Verification of fluid properties is the responsibility of the applicant, not the fluid suppliers.
(3) Prior to starting the endurance test, applicants should calibrate:
(a) All test equipment and measuring instrumentation necessary to operate and monitor the engine and the test facility to FAA-approved standards,
(b) All engine components according to their component calibration schedules.
(4) Applicants should maintain instrumentation calibration and measurement system accuracy throughout the duration of the test. This may be accomplished by verifying the posttest calibrations or using recognized and documented applicant procedures available to the FAA if requested.
e. Engine vibration signature. Applicants should establish the engine vibration signature during both pre-endurance and post-endurance tests by recording the vibration amplitudes as a function of engine rotor speed. Engine accelerometers mounted on the engine cases may be used to record the vibration data. Changes to the engine’s vibration signature over its operating range due to any part deterioration caused by the endurance test can be conveniently measured by comparing vibration surveys conducted before and after the test. Applicants should conduct these vibration surveys by applying slow accelerations and decelerations of not less than 2 minute durations that cover the range from minimum to maximum permissible rotor speeds, including any transient operations. Post-endurance test vibration signatures should not show a significant change from the data recorded during the pre-endurance vibration survey, and should still be at or below the allowable limits established for compliance with part 33 requirements.
The only purpose of the surveys conducted during endurance testing is to determine potential vibration signature changes due to engine deterioration. Applicants should address significant changes in vibrations to determine their causes and, if necessary, make applicable design changes; the test report should document all findings and actions taken.
f. Servicing and repairs during the endurance test.
(1) Applicants should monitor oil consumption during the test and ensure it remains within the allowable limits prescribed in the engine operating documents. If the oil consumption exceeds the allowable limits, the applicant should determine the cause and take corrective action during the test, or otherwise revise the engine manuals to reflect the consumption observed during the test. We also recommend that applicants periodically check oil samples for the presence of metallic particles or other debris that may indicate an impending failure of one or more parts.
(2) During the endurance tests, only servicing and minor repairs may be permitted by the ICA service and maintenance instructions, refer to § 33.99(b). Repairs that are normally required to aid in the engine reassembly after overhaul, such as drive shaft or stub shaft mating surface plating for assembly may be considered minor repairs.
(3) Section 33.99(b) requires that the applicant must subject the engine or its parts to additional test(s) or penalty test run(s) that we find necessary if during the endurance test, the frequency of service or the number of stops due to engine malfunction is excessive; or if a major repair or replacement of a part is found necessary; or because of findings from the teardown inspection.
(4) If an engine part fails during the test, the applicant should determine the cause of failure and assess the effect on the durability and operability of the engine. The applicant should determine and justify any corrective actions prior to resuming the test.
g. Endurance test report requirements.
(1) The certification test report(s) should contain sufficient data (for example, plots and tabulations) and discussion showing that the engine has successfully demonstrated compliance to all requirements of the calibration testing, endurance testing, and the teardown inspection regulations. In addition to test results and data analyses, the report should contain a list of engine faults and a complete description of all hardware distress, including any corrective actions that were implemented or are planned for implementation after the test.
(2) The report should also provide comparative tabulations (test results as related to § 33.87 requirements) of:
(a) The total time spent at each sequence of the endurance test cycle and associated power condition, and
(b) The minimum certificated parameter values obtained during each of those test cycle sequences.
(3) To show engine stabilization at or above the required operating parameter values, such as the rotor speed and gas temperature to be certificated, applicants should include a trace of one typical takeoff and idling cycle segment performed without any air bleed required by § 33.87(b)(1), and another for one acceleration and deceleration segment required by § 33.87(b)(5). These traces are necessary to prove that a parameter may not stabilize at its 100 percent value within §§ 33.87(b)(1) or § 33.87(b)(5) test segment. Applicants should provide supporting data showing that any deviations or exceptions to the test requirements are acceptable. This requirement also applies to the corresponding test runs of §§ 33.87(c), (d), (e),
(f), or (g).
(4) Appendix 6 of this AC provides additional information on test report requirements.
3-2. Specific Requirements in §§ 33.87(a)(1) through (a)(9). Unless otherwise specified, the guidance in the following paragraphs regarding § 33.87(b) requirements also applies to the corresponding test run requirements of §§ 33.87(c), (d), (e), (f), or (g).
a. Test sequence, § 33.87(a)(1). Applicants should follow the 6-hour endurance test cycle sequence prescribed in §§ 33.87(b) through (e) and the 2-hour test sequence in § 33.87(f) when applicable. We may allow test segments to be run out of their normal sequence when applicants have difficulty with readjusting the engine and test facility configuration to run all test segments sequentially, as prescribed. Applicants intending to run the tests with sequence changes should show that changes to the published endurance test cycle sequence(s) do not lessen the severity of the endurance test cycle. The applicant must also show that all test cycle requirements, including the required number of accelerations to rated power and decelerations back to idle power, were properly completed.
b. Automatic control of the engine, § 33.87(a)(2). Any automatic engine control that is part of the engine type design must control the engine operation during the endurance test, except for operations where manual, instead of automatic control is permitted, or where manual control is otherwise specified for a particular test run. Software used for engine control should be representative of the type design version. See paragraph 3-1.c of this AC for additional guidance related to test engine configuration.
c. Endurance test at redline conditions, § 33.87(a)(3).
(1) During the endurance test, the engine thrust or power, torque, gas temperature, and rotor shaft rotational speed(s) must be maintained simultaneously at least at 100 percent of the values associated with the particular engine operation being tested with exceptions under §§ 33.87(a)(5), (a)(6), and (a)(7). This means that applicants must run the endurance test to the maximum permissible (or redline) rotor speeds, gas temperature, and rated power, torque, or thrust values proposed for certification and prescribed in the engine TCDS. These parameters should achieve steady-state operating values with minimal fluctuations or cyclic type variations, and with any minimum variations remaining at or above the 100 percent values to be certificated.
(2) At each rating condition during the endurance test, the test engine must maintain rated power, thrust, or torque, which are the minimum physical power, thrust, or torque values meeting the definition in 14 CFR 1.1 and the requirements of §§ 33.7(a), (c), and 33.8(b). The rated power, thrust, or torque value that is prescribed in the TCDS is normally referenced to sea level, static, standard day pressure (14.696 psia or 101.3254 kilopascals) and the rated air temperature, with no customer air bleed or horsepower extraction allowed, an ideal inlet (100 percent ram pressure recovery), and engine inlet and exhaust test hardware as specified in the TCDS. See paragraphs 3-4.a.(2)(a) and (2)(b) of this AC for power or thrust setting adjustments and permitted power or thrust shortfalls.
(3) If the engine cannot achieve the rated minimum physical thrust or power requirement, then the applicant should present data or analysis that shows that any difference is inconsequential to the durability of those engine parts that are subject to thrust or power loads.
We will determine whether the showing is adequate or whether it requires an equivalent level of safety in accordance with § 21.21(b)(1).
(4) The ambient test conditions or the test engine configuration may not allow the engine to reach the triple redline test condition. In this case, the applicant may conduct more than one test, if necessary, so that all of the required testing at redline conditions is completed.
However, all endurance testing should be conducted on a single set of engine hardware.
(a) When the applicant proposes more than one endurance test, the second test should be run at the rated thrust with at least two redline conditions maintained simultaneously.
For turbopropeller and turboshaft engines, we will base the approval of torque and output shaft speed limits on those limits demonstrated simultaneously during the endurance test.
(b) Appendix 3 of this AC presents an example of an acceptable two-part test.
(5) If a parameter limit, such as rotor speed, for a particular engine rating, such as maximum continuous, is not defined, then the applicant should run the test segments associated with that rating condition to the maximum engine redline condition, as defined in the TCDS.
(6) For a transient overtemperature having the time limit greater than 30 seconds and less than or equal to 2 minutes, the applicant should apply the 100 percent gas temperature limit required by 33.87(a)(3) to the value of the transient overtemperature for the duration proposed.
The applicant should apply this transient overtemperature for each test period at takeoff power or thrust conditions, and for the entire time of all the 30-second periods at takeoff power or thrust, unless § 33.87(a)(7) applies. See appendix 7 of this AC for guidance on two-minute transient overtemperature limit approval.
d. Fuel and lubricating oil for endurance test, § 33.87(a)(4).
(1) The fuel, lubricating oil, and hydraulic fluid used for the endurance test must conform to the fuel, lubricating oil, and hydraulic fluid requirements listed in the TCDS and installation instructions.
(2) To verify that the lubrication system functions within design intent, the applicant should monitor oil consumption during the endurance test and summarize the results in the certification report. To verify oil type and quality, the applicant should take oil samples before and after the test, and analyze these samples to evaluate any oil property changes. The applicant should analyze the post-test sample for the presence of any metallic particles or other contamination that may indicate the deterioration of one or more engine parts. The applicant should disclose any evidence of oil property degradation or particle contamination in the test report. Additional oil sampling should be done during the test. The additional sampling will assist oil monitoring for particle contamination, which in turn will help to identify the beginning of significant part deterioration. The oil consumption rate, the system pressure, and temperature operating limits that were demonstrated during the endurance test should be consistent with any limits prescribed in the engine installation or operating instructions.
(3) The fuel characteristics should be consistent throughout the test and conform in all respects to the specifications prescribed in the TCDS. Applicants should disclose and justify any fluid property differences from these specifications, including the use of any additives. To establish a baseline, the applicant should take a fuel sample from the engine fuel supply line prior to the initial power or thrust calibration check. We may require additional sampling during the endurance test if fuel is used from sources other than the one from which the initial sample was taken.
e. Maximum air bleed testing, § 33.87(a)(5).
(1) The applicant should ensure that the maximum permissible total air bleed be extracted from the engine during at least five of the 25 endurance test cycles, except for the 30 second and 2-minute OEI test run under 33.87(f) (see paragraph e.(6) below). For these five test runs with the maximum air bleed, the regulation permits the power, thrust, or rotor speeds to be less than their 100 percent redline values; however, the gas temperature must be maintained to at least the 100 percent redline value. Any power, thrust, or rotor shaft rotational speed reduction should not exceed the reductions due to bleed extraction if the engine were in the type design configuration.
Note: We recommend that only five of the 25 endurance test cycles be run with maximum permissible air bleed flow to comply with the intent of § 33.87(a)(5). Running more than five of the endurance test cycles with maximum permissible air bleed flow may not allow the engine to demonstrate compliance to the intent of § 33.87(a)(3) and, therefore, should be avoided.
(2) In the test plan, the applicant should specify the total compressor air bleed flow rate limit and the proportional split from each compressor air bleed port on engines having multiple bleed ports. Examples of aircraft service air bleed uses are wing and cowling anti-ice, aircraft environmental control systems (for example, air conditioning), and engine cross-bleed starting.
During the endurance test, the applicant must demonstrate the maximum allowable air bleed flow rate and the individual air bleed port flow limits specified in the TCDS and in the § 33.5 manual.
(3) On engines with multiple air bleed ports, the air bled from each port should be extracted simultaneously at rates consistent with normal engine operation and design intent. The combined extraction should equal the total air bleed flow limit consistent with the rating condition being tested.
(4) During the test runs with maximum air bleed, the power or thrust or the rotor speed(s), or both, may be less than 100 percent of the value associated with the test condition, provided the following conditions are met:
(a) Any power or thrust or rotor shaft rotational speed reduction should not exceed reductions that would be due to air bleed extraction if the engine were in the type design configuration.
(b) The gas temperature must be maintained at least at 100 percent of the redline value at each power rating to be certified.
(5) The secondary airflow system, including the amount of air bleed for internal engine hardware cooling, should function as intended by the type design.
(6) For the test in § 33.87(f), an exception is permitted by the regulation to reduce test complexity and improve the flexibility necessary to attain key parameters, such as speed, temperature, and torque. For this test, applicants do not need to use maximum air bleed for engine and aircraft services if they show by test, or analysis based on test, that the engine’s ability to meet the teardown inspection requirements under § 33.93 is not enhanced. See paragraph 3-8.f. of this AC for guidance regarding what the analysis should include.
f. Accessory drive and mounting attachment loads, § 33.87(a)(6).
(1) Each accessory drive and mounting attachment must be loaded throughout the tests, either with the equipment listed in the applicant's assembly drawing or with facility units of a similar type. An exception is permitted by 33.87(a)(6)(iii) for the 30-second and 2-minute OEI test run under § 33.87(f) (see paragraph f.(5) below). The intent of this requirement is to simulate power extractions, weights, and overhung moments of the type design hardware for all operating power or thrust levels throughout the duration of the endurance test. However, the load imposed by each accessory used for aircraft service only should be the limit load consistent with rated power or thrust levels to be certified. The required loads for all other power or thrust levels are the normal operating loads.
(2) The accessory drives referred to above are typically for aircraft supplied equipment, such as starter, generator, gearbox spare drive, and engine components supplied by an airframe manufacturer. The mounting attachment points, including the mounting pads for accessory drive(s) and static structures, must also be loaded. Engine accessories, which are part of the engine type design, must be loaded for the conditions being tested.
(3) For any accessory drive and mounting attachment that cannot be adequately loaded or substantiated by the endurance test, the applicant should conduct additional component tests on a rig in accordance with §§ 33.87(a)(6) and 33.91, Component test, to establish that the components can function reliably in all anticipated engine operating conditions. For example, the main accessory gearbox may require both endurance rig testing and engine endurance testing to show compliance with § 33.87.
(4) When a gearbox rig test is necessary, the rig test is generally run at maximum drive-pad loading, maximum power extraction loading, and at extreme operating and environmental conditions to be approved. These extreme conditions may be outside of the engine endurance test set-up capability. In this example and during the engine endurance test, the gearbox drive position may have facility hardware, either actual or nonfunctioning, mounted to represent its weight and overhung moment.
(5) The applicant does not need to load the accessory drives and mounting attachments when running the test required for the 30-second and 2-minute OEI ratings under 33.87(f). In this case, the applicant should show that there is no effect on the durability of any accessory drive or engine component. If the accessory drives and mounting attachments are not loaded, the equivalent power should be added to the required power at the output drive. This will ensure that the power turbine rotor assembly is operated at or above the same levels it would be if the accessory drives and mounting attachments were loaded.
g. Redline gas temperature or oil temperature exclusion, and fuel, oil, and hydraulic fluid tests, § 33.87(a)(7).
(1) The regulation allows for an exception from testing at the 100 percent oil or exhaust gas temperature “where test periods are not longer than 5 minutes and do not allow stabilization.” This exception applies if at the end of any test period of 5 minutes or less, the type design characteristics of the engine are such that either the oil or exhaust gas temperature are still increasing and have not yet achieved their limiting value. To satisfy the requirements of this exception, the applicant should provide supporting data showing that these are the engine’s normal engine operating characteristics.
(2) The term “stabilization” of this requirement means that engine operating parameters, such as oil temperature or gas temperature, have achieved steady-state operating values with minimal fluctuations or cyclic type variations and any minimum variations remain at or above the 100 percent value to be certificated.
(3) To establish the time duration it takes for parameters to stabilize, the applicant should start measuring time from when the throttle is first moved from the minimum idle position toward the takeoff power position. Move the throttle from the minimum idle position to the takeoff power position within one second.
(4) The exception to the § 33.87(a)(7) requirement to maintain the gas temperature at the 100 percent or redline value does not apply to the 5-minute or longer runs at takeoff power or thrust during the 5-minute test periods in §§ 33.87(b)(1), (c)(1), (d)(1), and (e)(1). Nor does it apply to the 30-minute test periods in §§ 33.87(b)(2)(ii), (c)(2)(ii), (d)(2)(ii), and (e)(2). This means that the gas temperature must be stabilized at or above the 100 percent redline value before those 5-minute and 30-minute test periods, respectively, can begin. For most engines, the gas temperature does not generally require a 5-minute run period to stabilize at the redline value.
(5) For rotorcraft engines, the exception to the § 33.87(a)(7) requirement to maintain the gas temperature at the 100 percent or redline value to be certificated does not normally apply to the test periods rated continuous OEI, rated 30-minute OEI, 2 ½-minute OEI, 2-minute OEI, or even 30 second OEI runs.
(6) To request the exception to the gas temperature stabilization for the 30-second test run segments in § 33.87(b)(5), the applicant should follow the conditions specified in paragraph
3-4.b.(4)(b) of this AC. Similarly, for exceptions to §§ 33.87(c)(6), (d)(6), and (e)(2), follow the guidance as provided in the corresponding paragraphs 3-5.f, 3-6.e, and 3-7 of this AC.
(7) If the applicant demonstrates that the gas temperature stabilization exception is permitted during the 30-second test run segments in §§ 33.87(b)(5), (c)(6), (d)(6), and (e)(2), then the total run time that can be claimed at takeoff redline gas temperature should be reduced by the 1.25 hour duration of these segments. For example, the total run time that may be claimed at the takeoff redline gas temperature for compliance with § 33.87(b)(5) is reduced from 18.75 hours (accounting for the §§ 33.87(b)(1) and (2)(ii) segments and § 33.87(b)(5) segments) to
17.5 hours (which accounts for the §§ 33.87(b)(1) and (2)(ii) segments only). We will, however, still accept this reduced takeoff power redline run time to meet the redline gas temperature run time requirements of §§ 33.87(a)(3) and (a)(8).
(8) During the test segments run at gas temperature below the 100 percent redline, because the gas temperature stabilization exception is permitted, the applicant should maintain the rated thrust or power with rotor speeds (i.e., N1 and N2) at or above redline values.
(9) The applicant should qualify the engine with the same exhaust gas temperature stabilization characteristics that it will display in service.
(10) The applicant should control the engine using the same exhaust gas temperature measurement and control system that it will use in service.
(11) At least one endurance test cycle must be run with fuel, oil, and hydraulic fluid at the minimum pressure limit, and at least one endurance test cycle must be run with fuel, oil, and hydraulic fluid at the maximum pressure limit. During each of these two cycles, the fuel, oil, and hydraulic fluid pressures must be maintained at their maximum or minimum values simultaneously. The applicant may artificially adjust the fluid temperature with a test facility heat exchanger to achieve the desired value, or may use other means if it is shown not to affect the test outcome.
h. Transient overspeed, overtemperature, and overtorque demonstrations for a maximum period of 30 seconds, § 33.87(a)(8).
(1) Requested transient conditions that are being certified as part of an engine rating limitation must be demonstrated during the acceleration cycles required by §§ 33.87(b) through
(f), as applicable.
(2) A transient condition, referred to in § 33.87(a)(8), is rotor speed, gas temperature, or shaft torque value that exceeds the approved limit for a period of 30 seconds or less for transients associated with the takeoff, continuous OEI, and 30-minute OEI ratings. Applicants should limit rotor speed, gas temperature, or shaft torque transients associated with the 2 ½- minute, 2-minute, and 30-second OEI ratings to very brief periods of 10 seconds maximum.
Note: The FAA has approved transient overtemperatures that exceeded 30 seconds and up to 2 minutes. However, § 33.87(a)(8) is intended and remains suitable to evaluate rotor speed and gas temperature transient overtemperature for periods of 30 seconds or 15
less. See appendix 7 of this AC for guidance on two-minute transient overtemperature limit approval.
(3) Applicants may not use transient limits as supplementary limitations, regardless of their duration, for engine power setting purposes. The transient limits of shaft overspeed, gas overtemperature, and shaft overtorque prescribed in §§ 33.7(c)(14), (c)(15), and (c)(16), respectively, are intended for a transitory overshoot before reaching steady-state limit values following an engine acceleration in normal operation.
(a) If the number of occurrences of transient conditions up to 30 seconds is limited in normal engine operation, then the same number of accelerations required by §§ 33.87(b) through (g) must be made to the limiting transient conditions during the endurance test.
(b) If the number of occurrences of the transient conditions is not limited in normal engine operation, then at least 50 percent of the required endurance test accelerations must be made to the limiting transient conditions. For example, §§ 33.87(b)(1), (b)(2), and
(b)(5) require a total of 310 accelerations (150, 10, and 150, respectively) to takeoff power or thrust. Therefore, a minimum of 155 (50 percent of 310) accelerations must be made to the limiting takeoff power transient conditions during the endurance test.
(c) Section 33.87(a)(7) defines the basis for a possible exception to the requirement under § 33.87(a)(3) to maintain gas temperature at the 100 percent, or redline value, to be certificated during all takeoff test segments. Although an applicant may present data showing that an engine cannot achieve a stabilized takeoff redline gas temperature during the 30-second takeoff power segments under § 33.87(b)(5), these accelerations to takeoff power still count toward the total 310 accelerations required during the endurance test.
(4) We recommend conducting the transient condition test runs during the 150 accelerations to the 5-minute takeoff test segments of §§ 33.87(b)(1), (c)(1), (d)(1), and (e)(1) and during the 10 accelerations to the 30-minute takeoff test segments of §§ 33.87(b) (2)(ii), (c)
(2)(ii), (d) (2)(ii), and (e) (2). Some turbine engines, particularly large turbofan models, may not reach a stabilized gas temperature during the 30-second takeoff power segments of the test sequence under § 33.87(b)(5). We do not recommend attempting to run the transient tests during these segments, unless the transient duration to be certified is short enough to allow gas temperature stabilization at the required transient condition.
i. Additional test requirements for supersonic aircraft engines, § 33.87(a)(9). We may address the test requirements for supersonic aircraft engines in a future AC.
3-3. Special Topics.
a. Endurance test cycles for major design changes, parts manufacturer approvals (PMAs), repairs, and alterations.
(1) Applicants should consider the endurance test as an essential part of all major design change approvals, i.e., amended type certificates (TCs), supplemental type certificates 16
(STCs), and amended STCs. See appendix 8 of this AC for guidance on compliance with § 33.87 for engine TCs and major design changes, i.e., amended TCs, STCs, and amended STCs.
(2) Parts manufacturer approvals and major repairs and alterations may require running certain endurance testing for compliance with § 33.87. Advisory Circular 33.87-2, provides guidance on showing compliance with § 33.87 for PMAs by the means of comparative test methods.
b. Endurance test for multiple engine testing.
(1) When all engine parameters (thrust, power, torque, speed, and gas temperature) cannot be held at redline conditions simultaneously during the endurance test, then the applicant may conduct more than one test, so that all required testing is completed at redline conditions.
However, applicants should conduct all endurance testing on the same set of engine hardware to be presented for certification.
(2) Appendix 3 of this AC presents additional information on an acceptable endurance test cycle for multiple engine tests.
3-4. Endurance Test Schedule, § 33.87(b), for Engines Other Than Certain Rotorcraft Engines.
a. Explanation.
(1) The applicant must perform this endurance test cycle 25 times, for a total of 150 hours of testing on all turbojet, turbofan, and turbopropeller engines. The endurance test cycle is also required for rotorcraft turbine engines, except those rotorcraft engines for which the 30-minute OEI rating, continuous OEI rating, or 2½-minute OEI rating are desired. The 150 hours of testing time will accumulate 18.75 hours at takeoff power rating, 45 hours at maximum continuous power rating, 62.5 hours at incremental power step time period, and 23.75 hours at minimum idle condition. This endurance test cycle for § 33.87(b) is presented graphically in appendix 1, figures 1 and 2 of this AC.
(2) The test engine must maintain the rated power or thrust. Advisory Circular 33.7-1 provides information and guidance on the engine ratings and associated limitations. Specifically, the methods, ambient conditions, and engine configuration the applicant should use to establish and demonstrate the ratings that are then applied during the endurance test.
(a) The minimum physical power or thrust value required for testing under § 33.87(b) may be adjusted from the actual testing conditions to the conditions specified in the TCDS under which the rated power or thrust is determined. Applicants are not allowed to adjust the physically measured power or thrust to account for losses due to special test hardware that is incidental only to the conduct of the test. Special test hardware, such as fan inlet or exit guide vanes, an adjustable fan exhaust nozzle, or an altitude test cell, may be required to achieve simultaneous rotor shaft rotational speed and gas temperature redline conditions; however, the engine may not be able to produce physical rated power or thrust under these operating 17