Chapter 4. Teardown Inspection
4-1. General Requirements for All Endurance Tests (Except for Engines with 30-second OEI and 2-minute OEI Ratings), § 33.93(a). The applicant must completely disassemble each engine after the 150-hour endurance test under §§ 33.87(b), (c), (d), (e), or (g). For rotorcraft engines with 30-second OEI and 2-minute OEI ratings, the applicant may complete the endurance testing under §§ 33.87(b), (c), (d), or (e), and then start the testing under § 33.87(f) without intervening disassembly and inspection. For this option, the applicable teardown inspection requirements are those of § 33.93(a) instead of § 33.93(b). The FAA’s Manufacturing Inspection District Office inspector may need to witness the teardown inspection activities.
a. Section 33.93(a)(1). The applicant must verify that the adjustment setting and functioning characteristics of each engine component are within the limits established and recorded in compliance with § 33.82 before the endurance test. These components include, at the minimum, engine control system components, pumps, actuators, heat exchanger, and valves.
b. Section 33.93(a)(2).
(1) Explanation.
(a) The engine and engine parts or components must conform to their type design consisting of the data and information prescribed under § 21.31. In addition, allowances are permitted for used part conditions provided by the information submitted in compliance with § 33.4 or the TCDS, which includes the engine manual or overhaul manual limits, as applicable.
(b) The phrase, “eligible for incorporation into an engine for continued operation,” means that the installation of the part will continue to keep the engine in an airworthy condition.
An aircraft engine is “airworthy” when it conforms to its approved design and is in a condition for safe operation, see 14 CFR part 21.1(3)(b)(1).
(2) Guidance.
(a) The applicant should inspect all engine parts and components in both “dirty” and “cleaned” conditions using the ICA inspection instructions. The applicant should record the findings in the certification report. The engine parts and components must conform to their type design after accounting for allowances for used parts condition. Appendix 11 of this AC provides more detailed guidance for teardown inspections.
(b) The dirty inspection after the endurance test is necessary to preserve evidence that may be lost after cleaning, such as oil-coked parts, temperature affected parts, metal particles, and soot deposits. The applicant may conduct the dirty inspection at the individual part level, partial assembly, or complete assembly level. The degree of disassembly and dirty layout largely depends on observations made before and during disassembly of the engine or components. The applicant shouldn’t clean any engine part or fully disassemble the test engine without completing the dirty inspection at each step, or otherwise the applicant may request deviation from this guidance.
(c) The clean inspection should include the following:
1 A visual inspection for unacceptable wear, e.g., galling, distortion, or cracks.
2 A nondestructive inspection for cracks or incipient failures.
3 A dimensional inspection for wear, growth, rub, or distortion.
4 A visual, bench, or teardown inspection, or all, of controls, component, and accessory hardware.
(d) The applicant should use the results from the “dirty” and “clean” inspections to determine if the parts conform to the type design and are eligible to be re-installed in the engine for continued safe operation. The manufacturing inspector or designee should validate the applicant’s conformity inspection. The applicant should use the inspection limits in the engine manual or the overhaul manual (overhaul, heavy maintenance, shop manual, off-wing manual), as applicable. The applicant should document any part that no longer conforms to its type design in the test report.
(e) When an engine part exceeds the manual inspection limit(s), the applicant may:
1 Change the manual inspection limit to agree with the results of the endurance test. In this case, the applicant should show that the part conforming to the new manual inspection limits remains in airworthy condition between maintenance periods (e.g., inspections, shop visits, and overhaul) of the engine; or 2 Redesign the part to meet the manual inspection limit; or 3 Maintain the manual inspection limit, and (aa) Modify the frequency and procedures of the engine inspection program in the ICA to ensure that the part is inspected and removed from service before reaching the prescribed limit condition, and (bb) Identify in the test report any part condition that exceeds manual return-to-service limits and justifies part acceptability. The justification may be based on an engineering analysis and/or service experience from a part of similar type design and must show that the part in the existing condition is:
1) Still airworthy;
2) Capable to perform its design functions; and 35
3) Safe for continued engine operation between engine maintenance periods (inspection, shop visit, and overhaul) as scheduled in the ICA.
(f) In the ICA, the applicant may specify inspection and maintenance limits or criteria that are more conservative than those established for compliance with § 33.93.
(g) All engine components must pass post-test inspection and functional tests, such as a calibration test or a component acceptance test, when applicable, to ensure that the components are in a condition for continued safe operation and will perform satisfactorily until the next overhaul. Any component that fails the inspection or functional test, or is a new component using the test under § 33.87 as its sole endurance test, should be torn down for inspection. Newly designed components, components with major modifications, or components existing on other engine models with significantly different operating conditions would generally require a separate component test under § 33.91(a). For the component requiring a separate component test, we may waive the post-test teardown inspection after the tests under § 33.87 if the applicant shows that the component test condition is more severe than the endurance test, and if the teardown inspection will be performed after completing the component test.
(h) Certain repairs may be allowed for the endurance test. These are minor 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.
4-2. Teardown Inspection Requirements for Engines with 30-second OEI and 2-minute OEI Ratings, § 33.93(b) and (c).
a. After completing the test under § 33.87(f), the applicant should record the components’ adjustment settings and functional characteristics that can be established independent of installation on the engine. The applicant must show that these adjustment settings and functional characteristics remain within the limits that were established and recorded at the beginning of the test.
b. The test under § 33.87(f) for 30-second OEI and 2-minute OEI ratings is run following a 150-hour endurance test under §§ 33.87(b), (c), (d), or (e). Before starting the endurance test of § 33.87(f), the applicant may completely disassemble the test engine to show compliance to § 33.93(a).
c. Following completion of the test under § 33.87(f), the applicant must perform a teardown inspection based on the pass or fail criteria prescribed in § 33.93(b). The applicant must show that no failure of any significant engine component has occurred during the test or during the subsequent teardown inspection. For the purpose of this paragraph, engine components considered significant are those that can affect structural integrity, including, but not limited to, engine mounts, cases, bearing supports, shafts, and rotors. If any failure is seen, the failure should be analyzed. Further, the applicant should establish by test, analysis, or both, that the cause of the failure is corrected or that certain limitations are imposed on the engine.
d. The applicant may choose to not disassemble and inspect the engine after completion of the 150-hour endurance test and prior to starting the supplemental test under § 33.87(f). In this case, the applicant must perform the teardown inspection under § 33.93(a) at the end of the 2-hour supplemental test.
e. The applicant should document in the test report the component and engine part deterioration during the test under § 33.87(f). Such deterioration should not indicate a potentially hazardous condition for the engine. In addition to the damage that is readily visible, the applicant should detect and assess damage that is not visible. Such non-visible damage may include the effects of creep, stress rupture, metallurgical effects, or life usage. The applicant should consider this overall evaluation when defining and justifying the inspections and mandatory maintenance actions in the ICA. The ICA should include means to proper ly identify these component conditions, and should define appropriate maintenance actions for maintaining the continued airworthiness of the engine.
Appendix 1. Graphic Profiles of Endurance Test Schedules
1. Engines other than certain rotorcraft engines, § 33.87(b).
150-Hour Endurance Test Cycles 1-15 Figure 1
150-Hour Endurance Test Cycles 16-25 Figure 2
2. Rotorcraft engines with a 30-minute OEI power rating, § 33.87(c).
150-Hour Endurance Test Cycles 1-15 Figure 3
150-Hour Endurance Test Cycles 16-25 Figure 4
3. Rotorcraft engines with a continuous OEI rating, § 33.87(d).
150-Hour Endurance Test Cycles 1-15 Figure 5
150-Hour Endurance Test Cycles 16-25 Figure 6
4. Rotorcraft engines with a 2½ OEI rating, § 33.87(e).
a. § 33.87(b) and § 33.87(e)
150-Hour Endurance Test Cycles 1-15 Figure 7
150-Hour Endurance Test Cycles 16-25 Figure 8
b. § 33.87(c) and § 33.87(e)
150-Hour Endurance Test Cycles 1-25 Figure 9
c. § 33.87(d) and § 33.87(e)
150-Hour Endurance Test Cycles 1-15 Figure 10
150-Hour Endurance Test Cycles 16-25 Figure 11
5. Rotorcraft engines with 30-second and 2-minute OEI ratings, § 33.87(f).
2-Hour Supplemental Endurance Test, Cycle 1 of 4 Figure 12
2-Hour Supplemental Endurance Test, Cycles 2 through 4 Figure 13
A1-1
Figure 1. § 33.87(b), 150-Hour Endurance Test Cycles 1-15 03/09/15 Takeoff - Maximum - continuous A1-2 1/2 min.• -4 1/2 min.
Idle - $ le 5 min.
3 5 1/2 AC 33.87-1A Time ~ Hours
Figure 2. § 33.87(b), 150-Hour Endurance Test Cycles 16-25 03/09/15 Takeoff -
• 30 min.
Maximum - continuous A1-3 1/2 min.• -4 1/2 min.
Idle - → * 5 min.
1 11/2 5 1/2 AC 33.87-1A Time ~ Hours
Figure 3. § 33.87(c), 150-Hour Endurance Test Cycles 1-15 for Rotorcraft Engine with 30-Minute OEI Power Rating 30 Minute OEI A1-4 Pow er Idle Takeoff Maxim um Continuous 5 min.
30 min.
1/2 min.
4 1/2 min.
5 min.
0 1 2.5 3 5.5 6 Time ~ Hours 03/09/15 AC 33.87-1A
Figure 4. § 33.87(c), 150-Hour Endurance Test Cycles 16-25 for Rotorcraft Engine with 30-Minute OEI Power Rating 30 Minute OEI Pow er Idle Takeoff Maxim um Continuous 5 min.
1/2 min.
4 1/2 min.
5 min.
30 min.
30 min.
A1-5 0 1 2.5 3 5.5 6 Time ~ Hours 03/09/15 AC 33.87-1A
Figure 5. § 33.87(d), 150-Hour Endurance Test Cycles 1-15 for Rotorcraft Engine with Continuous OEI Power Rating A1-6
-4 1/2 min.
1/2 min.- • Figure 6. § 33.87(d), 150-Hour Endurance Test Cycles 16-25 for Rotorcraft Engine with Continuous OEI Power Rating • 1 hr. † 11/2 21/2 31/2 Time ~ Hours
• *- 5 min.
Continuous OEI- Takeoff - Maximum - continuous Idle - A1-7
Figure 7. § 33.87(e), 150-Hour Endurance Test Cycles 1-15 for Rotorcraft Engine with Rated 2 ½ Minute OEI Power Rating A1-8