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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Appendix 8. Endurance Test for Engine Certification and Showing of Compliance for
Engineering Changes
1. The endurance test is an essential part of all engine type certifications. The test may also be used to show compliance for engineering changes introduced by repairs and PMA applications.
We discuss acceptable means of compliance with § 33.87 for engine type certification and major design changes in the following paragraphs.
a. New type certificate. Run the endurance test as prescribed in §§ 33.87(a) and 33.87(b) through (g), as applicable, i.e., standard 150-hour endurance test, with no deviations.
b. Amended type certificate. Run the endurance test as prescribed in § 33.87(a) and the applicable endurance test cycle in §§ 33.87(b) through (g), with no deviations, unless one of the following conditions applies:
(1) The engine is a derivative model with minor or no design changes, and with the same or lower ratings and same or lower operating limitations, such that the original endurance test is still applicable.
(2) The engine is a derivative model with major design changes, and the same or lower ratings and operating limitations. These changes, if viewed individually or in combination, would have no impact on engine operability or durability within the approved ratings and limitations. Therefore, the data from the original endurance test would show compliance for the proposed hardware changes.
(3) The engine is a derivative model with major design changes, and the same or lower ratings and operating limitations, and for which we have determined that a repeat demonstration of the endurance test under §§ 33.87(b) through (g), as applicable, is needed to show compliance for the design change. Applicants must comply with all subparagraphs of § 33.87(a). We will determine:
1 Which subparagraphs of § 33.87(a) are affected by the proposed design changes, and require reevaluation by test, and 2 Which subparagraphs can be complied with by similarity using existing data from a prior applicable test under § 33.87.
(4) The above exceptions are based on the assumption that the applicant has conducted a standard endurance test on the original model or subsequent derivative model, in compliance with the requirements of § 33.87, such that the approved data from that previous test would apply.
c. Supplemental type certificate (STC) and amended STC. The applicant should identify the effects of the major design change on the validity of the endurance test run during the engine type certification. Compliance with all subparagraphs of § 33.87(a) is required. Our certifying office will determine which subparagraphs of § 33.87(a) are affected by the proposed design A8-1
changes and require reevaluation by test. The certifying office will also determine which subparagraphs have existing data from a test completed under § 33.87 for which compliance findings by similarity can be made. When the major design change requires a repeat demonstration of § 33.87, the applicant should run the applicable endurance test cycle prescribed in §§ 33.87(b) through (g), with no deviations.
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Appendix 9. Rotorcraft Operation with OEI Ratings and Endurance Test
1. Endurance Test for 30-second OEI and 2-minute OEI Ratings.
a. The maximum gross weight of a multi-engine rotorcraft is limited by the power available from the remaining operating engine(s) when one engine fails or is shutdown during flight.
b. In the event of an engine failure at the critical decision point (CDP) of an aircraft during takeoff or landing, a short burst of very high power, referred to as the 30-second OEI power, is required to complete the takeoff, or complete a rejected takeoff, or complete a balked landing.
This power level should enable the aircraft, at any point at or above CDP, to achieve continued flight, meet obstacle clearance requirements, and gain forward speed for taking off. At any point at an airspeed/altitude up to CDP, this power level should also enable the aircraft to safely complete a rejected takeoff. If the OEI condition occurs during landing, this high power level should be sufficient to lift the aircraft to a safe altitude, clear obstructions in the flight path, and initiate a climb out (balked landing).
c. A somewhat longer period of 2 minutes and at a lower power level, but still higher than takeoff power, referred to as 2-minute OEI power, is required to complete the climb out to a safe altitude and obtain the desired forward airspeed. Once the aircraft has reached the desired safe altitude and airspeed, a longer period at a lower power (still equal to or higher than maximum continuous power) is required to continue flight until a suitable landing site is reached. This power level will either be rated maximum continuous, 30-minute OEI, or continuous OEI power depending on the rating structure of the engine. For these reasons, the engine rating structure for a rotorcraft having 30-second OEI and 2-minute OEI is typically selected from one of the following three combinations of ratings:
(1) Maximum continuous, rated takeoff, and 30-second and 2-minute OEI.
(2) Maximum continuous, rated takeoff, 30-second and 2-minute OEI, and 30-minute OEI.
(3) Maximum continuous, rated takeoff, 30-second and 2-minute OEI, and continuous OEI.
d. For the endurance test, the test schedule is prescribed in § 33.87(f) for rotorcraft engines for which 30-second OEI and 2-minute OEI ratings are desired. The intent of this 2-hour test run is to assure that the engine is capable of producing these OEI rating powers in a deteriorated state. Therefore, this is an add-on test conducted separately on the same engine hardware after completion of a 150-hour endurance test under §§ 33.87(b), (c), (d), or (e).
2. Endurance Test for 2½-minute OEI Rating.
a. The 2½-minute OEI rating power is intended for the engine to perform similar functions as 30-second OEI and 2-minute OEI ratings in an OEI flight condition for a rotorcraft, but at a A9-1
generally lower power level relative to these two ratings. Similarly, the engine rating structure for a rotorcraft having 2½-minute OEI is typically selected from one of the following combinations of ratings:
(1) Maximum continuous, rated takeoff, and 2½-minute OEI.
(2) Maximum continuous, rated takeoff, 2½-minute OEI, and 30-minute OEI.
(3) Maximum continuous, rated takeoff, 2½-minute OEI, and continuous OEI.
b. The endurance test prescribed in § 33.87(e) applies to the above rating structures.
3. The Difference Between the OEI Ratings.
a. In rotorcraft operation, 30-second OEI and 2-minute OEI ratings perform very similar functions as 2½-minute OEI ratings. The significant difference between them is the limited use in service with mandatory inspection and maintenance actions for 30-second OEI and 2-minute OEI power ratings use. These two higher power ratings are intended to safely use available engine design margin for brief periods of exposure that may result in engine part or component deterioration beyond serviceable limits and, therefore, possibly be unavailable for further use.
b. The purpose of mandatory maintenance action is to restore the safety margin of the engine back to the level required in the airworthiness standards of part 33. Additionally, the teardown inspection standards differ as follows:
(1) The requirement for teardown inspection for a 2½-minute OEI rating after an endurance test under § 33.93(a) is that each engine part must be eligible for incorporation into an engine for continued operation in accordance with information submitted in compliance with § 33.4.
(2) The requirements for teardown inspection for 30-second and 2-minute OEI ratings under § 33.93(b) are that each engine part may exhibit deterioration in excess of that permitted under § 33.4, including some engine parts or components that may be unsuitable for further use, provided the structural integrity of the engine is maintained.
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Appendix 10. Accumulated Endurance Testing Times for § 33.87(e)
1. The endurance tests under § 33.87(e) for a 2½-minute OEI rating should be run in one of the following three combinations of ratings, as described in the “Guidance” section of § 33.87(e).
(a) Rated takeoff, maximum continuous, and 2½-minute OEI, or
(b) Rated takeoff, maximum continuous, 2½-minute OEI, and 30-minute OEI, or
(c) Rated takeoff, maximum continuous, 2½-minute OEI, and continuous OEI.
2. The accumulated testing times for 150 hours of testing of the three schedules are found in table 3, which represents the rating combinations in paragraph 1 above.
Table 3. Accumulated Test Times for Each Rating Combination Under 33.87(e) Time (in hours) at Indicated Power Level Schedule 2½ Min OEI 30 Min OEI Cont.
OEI Takeoff Max.
Cont.
Rotor Speed Steps Idle
(a) Rated takeoff, maximum continuous, and 2½-minute OEI
2.17* 16.58 45 62.50 23.75
(b) Rated takeoff, maximum continuous, 2½ minute OEI, and 30-minute OEI
2.17* 12.41** 11.67 37.5 62.50 23.75
(c) Rated takeoff, maximum continuous, 2½ minute OEI, and continuous OEI
2.17* 24.91*** 16.67 20 62.50 23.75 * 2.17 hours = 2 hours and 10 minutes.
** 12.41 hours = 12 hours and 25 minutes.
*** 24.91 hours = 24 hours and 55 minutes.
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Appendix 11. Teardown Inspection Requirements—Dirty Inspection and Clean Inspection
1. The FAA’s manufacturing inspector, project engineer, or authorized designees should witness the teardown inspection. Refer to Order 8110.4C paragraph 5-14 for the teardown inspection requirements. The teardown inspection consists of two parts—a dirty and a clean inspection. Applicants should conduct the dirty inspection at part level, partial assembly, subassembly, or assembly, without prior cleaning. The degree of disassembly largely depends on the findings of the engine and components before, during, or after disassembly.
2. Tear down inspection requirements.
a. Dirty inspection. At a minimum, the applicant should note the items listed below, and our manufacturing inspector should verify that the appearance of subassemblies and parts during the teardown is carefully noted.
(1) Component’s adjustment setting and functioning characteristics not within the limits established and recorded at the beginning of the endurance test;
(2) Any abnormal indication of leaks in valves, seals, or fittings;
(3) Indications of excessive or lack of lubrication;
(4) Excessive coking;
(5) Metal or foreign particles in the oil screens or passages;
(6) Sticking or broken parts;
(7) Lack of freedom of moving parts;
(8) Excessive breakaway torques; and
(9) Any other condition that may not be noticeable after complete disassembly and cleaning.
b. Clean inspection.
(1) Visual inspection. Thoroughly clean all engine parts and subassemblies.
(a) Visually inspect all engine parts for indications of galling, metallic pickup, corrosion, distortion, interference between moving parts, and cracks;
(b) Check parts for discoloration that may be due to excessive heat or lack of lubrication;
(c) Give special attention to bearings, gears, seals, or other rotating parts; and A11-1
(d) Inspect hot section parts for indications of cracking, overheating, or burning.
(2) Nondestructive inspection. Inspect highly stressed engine parts for cracks or incipient failures using suitable nondestructive testing methods, such as magnetic particle inspection, x-ray, penetrant, ultrasonic, or eddy current.
(3) Dimensionally inspect all critical engine parts that are subject to wear, growth, rubbing, or distortion to determine the extent of any changes that occurred during the test.
Dimensional changes may be determined by comparison of pre- and post-test dimensional measurements.
3. The applicant should submit the inspection report, as verified by our manufacturing inspector, as an attachment to the Conformity Inspection Record, FAA Form 8100.1. The applicant should include the inspection results in this report, giving a comprehensive description of all defects, failures, wear, or other unsatisfactory conditions, including photographs, as required. The manufacturing inspector should ensure that the applicant identified and retained all questionable parts in safe storage for review, if requested.
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Appendix 12. Historical Background for the Calibration Tests, Endurance Tests, and Teardown Inspection Requirements
1. General.
a. The basic requirements under § 33.87 regarding test cycles and testing at maximum thrust, power, torque, redline rotor speeds, and engine turbine gas temperatures have remained substantially the same since their introduction in 1958 and through amendment 2 of part 13 of the Civil Air Regulation (CAR), despite several regulatory reviews. These endurance test requirements constitute an inseparable part of the engine durability and operability certification process in part 33 that has provided an acceptable level of safety for aircraft gas turbine engines for more than five decades.
b. The endurance test cycle was not designed to represent a typical in-service flight cycle.
Instead, it represents an accelerated demonstration of durability, operability, and reliability with the engine operating at the power, thrust or torque, rotor speeds, and gas temperature limits for which it will be certificated.
2. Civil Air Regulation (CAR) 14 CFR part 13—Aircraft Engine Airworthiness.
a. CAR part 13, effective March 5, 1952. The Civil Aeronautics Board adopted a revised CAR part 13, on January 28, 1952. The Board promulgated the previously effective CAR part 13 in 1941. Part 13 remained substantially unchanged until 1952, and represented the first time turbine-type engine certification rules were included in the regulations. The Board designated general block tests, calibration tests, and a 150-hour endurance test for turbine engines as §§ 13.250, 252 and 254, respectively, in part 13. The technical content of the calibration test was similar to Federal Aviation Regulation (FAR) 14 CFR part 33.85(a), except that the CAR part 13 did not address compressor air bleed for the test. The CAR part 13 endurance test consisted of 30 run periods of 5 hours each, as specified by the test schedule. This endurance test resembled today’s FAR part 33.87(b)(1), but it used 91 percent takeoff, and 90 and 75 percent maximum continuous power or thrust test runs instead of §§ 33.87(b)(2) through 33.87(b)(4). Sections
33.87(b)(2) through 33.87(b)(4) today specify the testing at maximum continuous, takeoff, and incremental cruise power or thrust. The CAR part 13 teardown inspection under § 13.256 required a complete engine disassembly and detailed inspection of the tested engine to check for fatigue and wear.
b. CAR part 13, amendment 13-1, effective August 12, 1957.
(1) This amendment revised two subparagraphs in the endurance test schedule from “91 percent takeoff” and “90 percent and 75 percent maximum continuous power/thrust” to “Takeoff and idling” and “Incremental cruise power and/or thrust,” respectively, which made these two essentially the same as the FAR §§ 33.87(b)(2) and 33.87(b)(4).
(2) Other revisions were:
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