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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(a) The addition of a requirement that during the endurance test, the engine power/thrust and rotational speeds be controlled within +/- 3 percent of the specified value.
(b) The addition of test requirements for engines with an augmented power or thrust rating.
(c) The addition of maximum gas temperature and oil temperature requirements at all engine rating runs during the test, which is same as the equivalent requirements in § 33.87(a)(7).
c. CAR part 13, amendment 13-2, effective May 17, 1958. This amendment revised the specification of power and/or thrust and of engine rotational speed of a tolerance in the endurance test from “+/- 3 percent of the specified values” to “at not less than 100 percent of the specified values.”
d. CAR part 13, amendment 13-5, effective February 12, 1963. This amendment revised part 13 by defining and adding a new rating, “30-minute power for helicopter turbine engines,” and adding a new test schedule to § 13.254, Endurance test, for substantiating this rated power for turbine engines used in rotorcraft. The technical content of this new schedule is essentially the same as the FAR part 33.87(c), “Rotorcraft engines for which a 30-minute OEI power rating is desired.”
e. CAR part 13, amendment 13-6, effective April 22, 1964. This amendment established a 2½-minute power rating for a one engine inoperative (OEI) event at any instant after the start of takeoff for multi-engine rotorcraft. This was accomplished by defining and adding a new rating, “2½-minute power for helicopter turbine engines,” and adding a new test schedule to § 13.254(c) for an engine with a “2½-minute power” and a “30-minute power” to substantiate these rated powers. The test requirements for these ratings are essentially the same as § 33.87(e), except:
(1) Section 33.87(e)(2) allows three OEI rating combinations for rotorcraft performance needs, while the CAR § 13.254(c) allowed only the following option (b). The options allowed by FAR § 33.87(e)(2) are:
(a) 2½-minute OEI/maximum continuous,
(b) 2½-minute OEI/30-minute OEI, and
(c) 2½-minute OEI/continuous OEI ratings.
(2) Section 33.87(e)(2) requires that the last 5 minutes of the 30-minute OEI in one of the endurance test cycles be run to 2½-minute OEI power, while the CAR § 13.254(c) does not.
Note: Section 13.250, General block tests, § 13.252, Calibration test, and § 13.256, Teardown inspections remained unchanged through amendment 13-6.
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3. 14 CFR, part 33 – Airworthiness Standards: Aircraft Engines.
a. Part 33, effective February 1, 1965.
(1) The new 14 CFR part 33 of the FAA recodification program was issued to replace the airworthiness requirements contained in part 13 of the CAR.
(2) Section 33.85, Calibration tests, is the same as its equivalent paragraph in the CAR part 13, except for an additional requirement that the engine power control be adjusted to produce the maximum allowable gas temperatures and rotor speeds at takeoff operating conditions before the endurance test, and may not be changed during calibration tests and the endurance test.
(3) The contents of §§ 33.87, Endurance test and 33.93, Teardown inspections are the same as their equivalent paragraphs in the CAR part 13, except for minor editorial differences.
(4) Section 33.99, General conduct of block tests was completely revised from its equivalent paragraph in the CAR part 13.
b. Part 33, amendment 6, effective October 31, 1974.
(1) The new § 33.82, General, adopted by this amendment, requires the applicant to establish and record certain adjustment settings and functioning characteristics of engine components before starting the endurance test. This paragraph is the same in the current regulations.
(2) Section 33.85(a) of the calibration test was revised to include only the compressor air bleed essential for engine functioning during the test. Section 33.85(b) was revised to the current regulation. Both paragraphs now agree with the current regulation.
(3) Section 33.87, Endurance test, was revised in response to the increasing complexity of airframes, engines, and their interfaces. This amendment added § 33.87(a)(3) to address the allowance for multiple engine tests when all engine parameters could not be held simultaneously at the 100 percent level that was to be certified. We made this change based on our certification experience with high-bypass large turbofan engine certifications. Section 33.87 was revised by:
(a) Expanding § 33.87(a) to the current requirements, except:
1 The test may be run at reduced power or thrust or rotor speeds below the 100 percent value specified in § 33.87(a)(3) during maximum air bleed runs, and 2 The testing of accessory drives and mounting attachments may be accomplished on a rig in § 33.87(a)(6).
(b) Including the endurance test schedule for supersonic aircraft engine.
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(4) Section 33.93(a), Teardown inspection, was revised to the current requirements.
(5) Section 33.99, General conduct of block tests, was revised to the current regulation by adding requirements for engine service, malfunction, and stoppage during endurance test.
c. Part 33, amendment 10, effective March 26, 1984.
(1) Section 33.87, Endurance test, was revised as follows:
(a) Sections 33.87(a)(3) and (a)(5) were revised to allow the applicant to reduce power or thrust or rotor speeds below the 100 percent value specified in § 33.87(a)(3) during maximum compressor air bleed runs, as it is not always possible to reach redline speeds at takeoff and maximum continuous thrust/power without exceeding gas temperature limits.
(b) Section 33.87(a)(6) was revised to allow separate rig testing of accessory drives and mounting attachments.
(c) A new requirement was added to specify that the rated 2½-minute OEI power must be applied during the last 25th cycle of the endurance test. Specifically, the 2½- minute OEI power must be applied during the last 5 minutes of the 30-minute run for the rated 30-minute OEI.
(d) The above changes updated §§ 33.87(a)(3), (a)(5), and (a)(6) to the current requirements.
d. Part 33, amendment 12, effective October 3, 1988.
(1) In § 1.1, the existing definitions of “2½-minute power” and “30-minute power” were revised to read: “2½-minute OEI power” and “30-minute OEI power” to make these definitions relate more closely to the name of these power ratings with their intended use. A new definition of “continuous OEI power” was introduced.
(2) In § 33.87, the new test schedule for an engine with a “continuous OEI power” rating was added to the endurance test as § 33.87(d).
e. Part 33, amendment 18, effective August 19, 1996.
(1) This amendment adopted new 30-second OEI and 2-minute OEI ratings applicable to rotorcraft turbine engines.
(2) New definitions of, “30-second OEI power” and “2-minute OEI power” ratings were introduced in § 1.1.
(3) Section 33.85 was revised by adding new paragraphs (c) and (d) to cover specific calibration test requirements for these two OEI ratings.
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(4) Section 33.87 was revised by adding a new 2-hour test schedule to paragraph (f) for the ratings.
(5) Section 33.93 was revised by adding new paragraphs (b) and (c) that define teardown inspection requirements after completion of the 2-hour endurance test in § 33.87(f).
f. Part 33, amendment 25, effective October 17, 2008. This change amended the endurance test and tear down inspection requirements for certain OEI ratings. This amendment was the result of a harmonization effort of a working group comprised of representatives of the FAA, the Joint Aviation Authorities (JAA), Transport Canada, and industry. The European Aviation Safety Agency (EASA) subsequently adopted these new requirements as part of its Certification Specifications for Engines.
(1) Revised § 1.1, General definitions, for all rated OEI powers by adding a second condition, an engine shutdown, to the failure condition that defines an OEI. Also revised the use for the 2½-minute OEI rating from “a period of use” to “periods of use” to be consistent with the usage definitions of 30-second OEI and 2-minute OEI ratings.
(2) Revised § 33.87(a)(6) to allow the applicant to run the tests under §§ 33.87(f)(1) through (f)(8) without loading the accessory drives and mounting attachments if the applicant can substantiate that the durability of any accessory drive or engine component is not significantly affected and if the equivalent power is added to the output drive shaft.
(3) Revised § 33.87(a)(5) to exempt engines with 30-second and 2-minute OEI ratings from testing with maximum air bleed if the applicant can show by testing, or analysis based on testing, that the validity of the endurance test is preserved.
(4) Added a requirement that the test schedule for 30-second and 2-minute OEI ratings in § 33.87(f) be run continuously without stopping.
(5) Clarified the test schedule in § 33.87(f)(4) related to 30-second and 2-minute OEI ratings.
(6) Revised the test schedule in § 33.87(c) related to 30-minute OEI rating to agree with the schedule in EASA’s certification specifications for engines. The result harmonizes the endurance test schedule for engines with a 30-minute OEI rating.
(7) Clarified the idle condition of § 33.87(f)(8) as flight idle.
(8) Revised § 33.93(b)(2) by replacing the parts or components identified as, “mounts, cases, bearing supports, shafts, and rotors,” with, “the engine,” to emphasize that after the test, the applicant needs to inspect and consider deterioration of any engine component that could affect the structural integrity of the engine, not just those listed above.
g. Part 33, amendment 30, effective November 2, 2009. This amendment added the transient engine overtorque and maximum engine overtorque. This amendment harmonized A12-5
FAA and EASA standards and simplified airworthiness approvals for the import and export of turbopropeller and turboshaft engines with free power turbines.
(1) Added in § 1.1, General definitions, the maximum engine overtorque.
(2) Added new engine limitations in § 33.7(16) for transient engine overtorque and § 33.7(17) maximum engine overtorque for turbopropeller and turboshaft engines incorporating free power turbines.
(3) Added new section, § 33.84, engine overtorque test that contains requirements for testing performed under § 33.87 endurance test.
(4) Revised § 33.87(a)(8) by adding the transient engine overtorque.
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_________________________________________________________________ _________________________________________________________________ _________________________________________________________________ ________________________________________________________________ Appendix 13. Advisory Circular Feedback Information If you have comments or recommendations for improving this AC, or suggestions for new items or subjects to be added, or if you find an error, you may let us know about it by using this page as a template and 1) emailing it to 9-AWA-AVS-AIR500-Coord@faa.gov, or 2) faxing it to the attention of the AIR Directives Management Officer at 202-267-3983.
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