a. Explanation……17
b. Guidance………18
3-5. Endurance Test Schedule, § 33.87(c), for Rotorcraft Engines for which a
30-minute OEI Power Rating is Desired23
a. Guidance………23
b. Section 33.87(c)(1), Takeoff and idling23
c. Section 33.87(c)(2), Rated maximum continuous and takeoff power23
d. Section 33.87(c)(3) Rated maximum continuous power24
e. Section 33.87(c)(4), Rated 30-minute OEI power24
f. Sections 33.87(c)(5), Incremental cruise power or thrust; 33.87(c)(6)
Acceleration and deceleration runs; and 33.87(c)(7), Starts24
3-6. Endurance Test Schedule, § 33.87(d), for Rotorcraft Engines for which a
Continuous OEI Rating is Desired24
a. Guidance24
b. Section 33.87(d)(1), Takeoff and idling, and § 33.87(d)(2), Rated maximum
continuous and takeoff power25
c. Section 33.87(d)(3), Rated continuous OEI power25
d. Section 33.87(d)(4), Rated maximum continuous power25
e. Section 33.87(d)(5), Incremental cruise power, § 33.87(d)(6), Acceleration, and
deceleration runs, and § 33.87(d)(7), Starts25
3-7. Endurance Test Schedule, § 33.87(e), for Rotorcraft Engines for which a 2½-minute
OEI Power Rating is Desired26
a. Explanation26
b. Guidance26
3-8. Endurance Test Schedule, § 33.87(f), for Rotorcraft Engines for which 30-second
OEI and 2-minute OEI Ratings are Desired27
a. The 30-second OEI and 2-minute OEI power ratings27
b. Endurance test for 30-second and 2- minute OEI ratings28
c. Test conduct28
d. Test sequences28
e. Test time29
f. Air bleed during test31
g. Accessory drives and mounting attachments31
h. Engine operating limitations32
3-9. Endurance Test Schedule, § 33.87(g), Supersonic A ircraft Engines32
v
3-10. Endurance Test Schedule, § 33.84, Engine Overtorque T est32
a. Maximum engine overtorque test, § 33.8432
b. Maximum engine overtorque32
c. Test conditions32
d Post-test engine inspection33
Chapter 4. Teardown Inspection34
4-1. General Requirements for All Endurance Tests (Except for Engines with
30-second OEI and 2-minute OEI Ratings), § 33.93(a)34
a. Section 33.93(a)(1)34
b. Section 33.93(a)(2)34
4-2. Teardown Inspection Requirements for Engines with 30-second OEI and ....................
2-minute OEI Ratings, § 33.93(b) and (c)36
Appendix 1. Graphic Profiles of Endurance Test SchedulesA1-1
1. Engines other than certain rotorcraft engines, § 33.87(b)A1-1
2. Rotorcraft engines with a 30-minute OEI power rating, § 33.87(c)A1-1
3. Rotorcraft engines with a continuous OEI rating, § 33.87(d)A1-1
4. Rotorcraft engines with a 2½ OEI rating, § 33.87(e)A1-1
a. § 33.87(b) and § 33.87(e)A1-1
b. § 33.87(c) and § 33.87(e)A1-1
c. § 33.87(d) and § 33.87(e)A1-1
5. Rotorcraft engines with a 30-second and 2-minute OEI ratings, § 33.87(f)A1-1
Appendix 2. Endurance Test Plan RequirementsA2-1
Appendix 3. Endurance Test Cycle for Multiple Engine TestsA3-1
1. Regulatory basis for multiple engine testsA3-1
2. Example of multiple engine testsA3-1
Appendix 4. Engine Configuration Modifications in Endurance TestA4-1
Appendix 5. Endurance Test Conformity Inspections and Type Inspection
AuthorizationA5-1
Appendix 6. Test Reports RequirementsA6-1
Appendix 7. Endurance Testing for a Two-Minute Transient Overtemperature Limit
ApprovalA7-1
vi
1. ExplanationA7-1
2. GuidanceA7-1
Appendix 8. Endurance Test for Engine Certification and Showing of Compliance for
Engineering ChangesA8-1
Appendix 9. Rotorcraft Operation with OEI Ratings and Endurance TestA9-1
1. Endurance Test for 30-second OEI and 2-minute OEI RatingsA9-1
2. Endurance Test for 2½-minute OEI RatingA9-1
3. The Difference Between the OEI RatingsA9-2
Appendix 10. Accumulated Endurance Testing Times for §33.87(e)A10-1
Appendix 11. Teardown Inspection Requirements—Dirty Inspection and Clean
InspectionA11-1
Appendix 12. Historical Background for the Calibration Tests, Endurance Tests, and
Teardown Inspection RequirementsA12-1
1. GeneralA12-1
2. Civil Air Regulation (CAR) 14 CFR, part 13 – Aircraft Engine Airworthiness. A12-1
a. CAR part 13, effective March 5, 1952A12-1
b. CAR part 13, amendment 13-1, effective August 8, 1957A12-1
c. CAR part 13, amendment 13-2, effective May 17, 1958A12-2
d. CAR part 13, amendment 13-5, effective February 12, 1963A12-2
e. CAR part 13, amendment 13-6, effective April 22, 1964A12-2
3. 14 CFR, part 33 – Airworthiness Standards: Aircraft EnginesA12-3
a. Part 33, effective February 2, 1965A12-3
b. Part 33, amendment 6, effective October 31, 1974A12-3
c. Part 33, amendment 10, effective March 26, 1984A12-4
d. Part 33, amendment 12, effective October 3, 1988A12-4
e. Part 33, amendment 18, effective August 19, 1996A12-4
f. Part 33, amendment 25, effective October 17, 2008A12-5
g. Part 33, amendment 30, effective November 2, 2009A12-5
vii
Chapter 1. General
1-1. Definitions. The following definitions apply to the terms used in this AC.
a. Engine component. Systems and accessories that are part of the engine type design.
b. Endurance test cycle. The series of runs or sequences prescribed in each §§ 33.87(b) through (g).
c. Germane or primary hardware. The hardware used in the certification test that is affected by, or directly affects the outcome of the certification test and the pass or fail criteria for the given test objectives.
d. Redline conditions. The highest physical rotor speed, gas temperature, or output shaft torque, including transients, which may not be exceeded during operation at any applicable rating. The type certificate data sheet (TCDS) prescribes the limitations for each approved engine rating.
e. Test hardware. The parts and components assembled on the engine and to be tested, or, if not mounted on the engine, are part of the engine type design. The test hardware may deviate from the type design if it remains representative of the type design and the applicant justifies the differences in the test plan. This justification is frequently referred to as “reconciliation.”
f. Triple redline test condition. The engine operation at simultaneous redline rotor speeds, redline gas temperature, and full rated thrust or torque, as required by § 33.87(a)(3). For example, for a two-shaft system engine, the engine operation at simultaneous redlines of the two rotor speeds (e.g. low pressure and high pressure rotor systems) and redline gas temperature, in addition to full rated thrust or torque.
Chapter 2. Calibration Tests
2-1. Power Characteristics.
a. The power characteristics should be established based on the endurance test of the engine that represents the type design and is in the following configuration:
(1) No air bleed for aircraft services, and
(2) With only those accessories installed that are essential for engine functioning, except when the TCDS defines other conditions that are used to determine the engine ratings.
b. The test data is then referenced to the standard atmosphere conditions for which the engine rating is defined.
2-2. General Requirements in §§ 33.85(a), 33.85(b), and 33.85(c).
a. The pre- and post-endurance calibration tests required by § 33.85, establish the engine’s power characteristics in the type design configuration over its entire operating range of speeds, pressures, and temperatures. These tests provide the means for measuring the engine deterioration caused by the endurance test.
b. To identify the changes in engine power characteristics that may occur during the engine endurance test of § 33.87, applicants must compare the engine’s power characteristics established before and after the endurance test, except as provided by § 33.85(d) for the 30 second and 2-minute OEI ratings. This exception is further discussed in paragraph 2-3 of this AC.
c. Applicants should run the calibration tests with a clean inlet and exhaust, and without special test equipment, such as inlet screen, pre-swirler, mixer screen, or non-type design exhaust nozzles. In addition, the facility hardware must be similar to a production test cell (e.g., engine cowling, bell mouth, and normal engine control schedules). When special test equipment is necessary to obtain simultaneous redline conditions during the endurance test, applicants must address the engine configuration changes. See paragraph 3-1.c. and appendix 4 of this AC for further guidance. The power settings should include the highest power or thrust rating capability of the engine during the initial and final power calibrations. 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.
d. The calibration test data should show that following completion of the endurance test, the engine is capable of producing its rated power or thrust without exceeding any speed, gas temperature, or operating limit(s) specified in the TCDS.
e. The applicant should record the calibration test measurements only after the engine operating condition stabilizes at each rating condition. The only exception is the recording of data at the 30-second and 2-minute OEI rating conditions described in § 33.85(d), during which the gas temperature need not be stabilized at the end of the rating time limit.
2-3. Provisions for 30-second and 2-minute OEI Ratings, § 33.85(d). The extended engine operation at the 30-second OEI and 2-minute OEI ratings during calibration testing could increase hardware deterioration beyond what the endurance test would demonstrate for the ratings alone. Therefore, the data recorded during the OEI power segments in § 33.87(f) may be used toward compliance with the calibration test requirements of these two ratings. However, the applicant should record this data during the first and last test cycle to properly represent the pretest and post-test performance capability of the engine. The following paragraphs in this section provide guidance on how the data from § 33.87 may be used to support compliance with § 33.85.
a. The applicant should determine the engine’s power characteristics at the 30-second and 2-minute OEI rating conditions. These power characteristics should include deterioration determined from the pretest calibration prior to the endurance test of § 33.87(f), up to and including the third test sequence of the 30-second rated power. The power deterioration through the third test sequence should be the best indicator of the worst-case power deterioration that could occur during actual usage at the rating. This data must be included in the installation manual to define performance characteristics of the engine.
b. If power deterioration exceeds 10 percent at the 30-second rating over the course of the 2-hour test in § 33.87(f), and even if the engine still produces rated power at the end of the test, the applicant should evaluate the mode of deterioration to ensure that the availability of 30 second rated power in service will not be compromised by deterioration variability.
c. In addition to the calibration data from § 33.85(d), any available information from tests in §§ 33.88 and 33.90 should also be used to establish the engine characteristics throughout the engine operating envelope.
Chapter 3. Endurance Test
3-1. General Requirements in § 33.87(a).
a. The endurance test. The endurance test is not a simulation of expected in- service operation, but an accelerated severity test intended to demonstrate a minimum level of engine operability and durability within the approved engine ratings and operating limitations.
(1) The test requirements of §§ 33.87(b), (c), (d), (e), or (g) are to demonstrate that at the end of the test, the engine conforms to its type design and is safe for continued operation.
The requirement for § 33.87(f) is to demonstrate that at the end of the supplemental test, at a minimum, the structural integrity of the engine is maintained. This determination should be based on the inspection and maintenance requirements that are defined in the instructions for continued airworthiness (ICA) that will be submitted in compliance with § 33.4. To demonstrate this minimum level of durability and operability, the engine should:
(a) Continue to produce its rated power or thrust at the end of the test in §§ 33.87(b), (c), (d), (e), or (g) without exceeding any of the operating limitations defined by compliance with §§ 33.4, 33.5, and 33.7 and prescribed in the TCDS.
(b) Demonstrate acceptable operability from minimum to rated takeoff power or thrust without overtemperature, surge, stall, or other detrimental occurrences.
(c) Demonstrate durability while operating up to rated thrust, power, or torque;
redline and transient rotor speeds and gas temperatures; and when applying maximum rated loads on accessory drives and mounting attachments.
(d) Demonstrate the maximum compressor bleed air capability for engine and aircraft use. Paragraph 3-2.e. of this AC provides guidance for maximum compressor bleed air.
(e) Demonstrate acceptable operation at minimum and maximum fuel and hydraulic fluid pressure limit conditions. Advisory Circular 33.7-1 provides information and guidance on the fuel pressure limit locations.
(f) Demonstrate acceptable operation at the minimum and maximum lubrication oil pressure and temperature limit conditions.
(g) Demonstrate starting capability and drainage or expulsion of unwanted fluids or fuel that may accumulate after a false start.
(2) The test engine may also be used for other part 33 engine tests in conjunction with the endurance test runs. In addition, the data and results from the endurance test may also be used to show compliance to other part 33 regulations. These regulations may include:
(a) Engine ratings and operating limitations in § 33.7.
(b) Engine power and thrust settings in § 33.8(b).
(c) Suitability and durability of materials in § 33.15.
(d) Fluid drainage demonstration in § 33.17(f).
(e) Durability in § 33.19(a).
(f) Accessory attachments in § 33.25.
(g) Surge and stall characteristics in § 33.65.
(h) Bleed air systems in § 33.66 and bleed and power extraction in § 33.89.
(i) Ignition system function in § 33.69.
(j) Fuel system in § 33.67(a) and (b).
(k) Lubrication system, § 33.71(a) and (b).
(l) Hydraulic actuating systems, § 33.72.
(m) Power or thrust response, § 33.73, and acceleration time in § 33.89(a).
(n) Engine-propeller system tests for turbopropeller engines in § 33.95.
(o) Thrust reverser test in § 33.97.
(p) Fuel venting emissions in Subpart B of 14 CFR part 34.
(3) The general endurance test requirements specified in § 33.82, the calibration test in § 33.85, the endurance test in § 33.87, the teardown inspection in § 33.93, and the general conduct of block test requirements specified in § 33.99 form integral parts of the engine’s endurance testing. However, some systems or components may not be adequately substantiated by endurance testing alone under the requirements of § 33.87. For these systems or components, applicants should complete additional component level tests under the requirements defined in § 33.91 to establish that the systems, or components, can function reliably in all engine operating and atmospheric conditions that will be certificated. For example, to properly demonstrate its operability and durability characteristics, the main accessory gearbox must be tested at the maximum rated pad loads and power extraction loads that will be certified. If these extreme gearbox load conditions exceed the capability of the applicant’s endurance testing facilities, then the applicant may choose to complete an additional gearbox rig test at these maximum rating conditions.
(4) The endurance test must include at least 150 hours of testing in accordance with the series of test schedules specified in §§ 33.87(b), (c), (d), (e), and (g), depending upon the type 5
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.