Initial Maintenance Inspection (IMI), 14 CFR 33.90, Test for Turbine Engines

04/13/2016 AC 33.90-1A 2.1.2.2 Consideration of Hardware Items Not Part of Engine Type Design.

You should consider for test inclusion other hardware items not normally part of the engine type design (for example, thrust reverser, air starter, engine build-up hardware). Including such hardware may: • Produce more realistic engine loads.

• Increase test time for the non-engine components.

Consult the aircraft manufacturer for information on this hardware or installation configuration.

2.1.2.3 Engine Test Configuration.

You should conduct the IMI test when the engine is installed in a typical configuration, to the maximum extent possible. For example, you should: • Connect and operate, in a way representative of service, airframe accessories and interfaces that load the engine.

• Schedule, throughout the test, typical accessory loads and bleed air extraction that would be experienced during the engine flight cycle.

2.1.2.4 Turboprop Applications.

For turboprop applications, perform the test run with an installation-eligible propeller installed. Incorporate into the test cycle applicable design features, such as: • Propeller braking.

• Auxiliary power unit (APU)-mode operation(s).

2.1.2.5 Turboshaft Applications.

For turboshaft applications, you should load the test engine output shaft to simulate the appropriate rotor drive system characteristics of the intended installation. Potential rotor drive system characteristics include, but are not limited to, inertial and torsional vibration.

Test Parameters. 2.1.3 You may conduct the test at standard day conditions, if those conditions effectively represent the conditions expected during an engine flight cycle, including: • Power/thrust.

• Stress.

• Component temperature.

• EGT.

• Unbalance vibration.

2-3 04/13/2016 AC 33.90-1A Test Duration. 2.1.4 The total number of test cycles and test duration should be equivalent to the anticipated initial on-wing life for the new engine model in a typical installation. At a minimum, you will need to: • Run a suitable number of cycles to establish the IMI interval(s).

• Demonstrate that a type design engine remains in a serviceable condition between required maintenance inspections.

The regulation does not require a fixed number of cycles (i.e., the IMI is not a "1,000-cycle" test). However, you must correlate the number of cycles you propose for the test to the planned engine inspection intervals. See paragraph 2.1.6 of this AC.

Pass/Fail Criteria. 2.1.5 2.1.5.1 General.

The engine type design will meet the requirements of § 33.90 when the post-test, IMI hardware condition demonstrates that the engine will remain airworthy for the proposed intervals. The engine should comply with paragraph 2.1.5.2 , paragraph 2.1.5.3 , and paragraph 2.1.5.4 of this AC.

2.1.5.2 Test Duration.

Over the test duration, and when you follow normal ICA maintenance practices, the engine must: • Meet all proposed thrust or power ratings without exceeding any operating limitations.

• Be free of significant anomalies (for example, surge, stall) when operated per the operating instructions provided in support of § 33.5.

2.1.5.3 Post-Teardown Inspection.

A post-test teardown inspection should demonstrate that each engine part: • Conforms to the type design.

• Is eligible for continued operation in service.

You may find hardware serviceable if you include, within the ICA, appropriate inspections or limitations.

2-4 04/13/2016 AC 33.90-1A 2.1.5.4 Certification Documentation.

The certification documentation should identify those parts of the engine that will have specific ICA requirements or recommendations that result from the IMI test. The final ICA should include these specific requirements and or recommendations, per the existing provisions of § 33.4, including: • Life limits.

• Inspections.

• Intervals.

• Accept/reject criteria.

Determination of Time/Cycle IMI Intervals. 2.1.6 2.1.6.1 Full Cycle Test.

For a successful full cycle test, you may use the full number of cycles and full number of hours demonstrated during the test as the IMI interval.

2.1.6.2 Accelerated Severity Cycle Test.

For a successful accelerated severity cycle test, you may use the full number of cycles for those engine parts for which the test cycle was shown to be equal to or more severe than the assumed engine flight cycle.

2.1.6.3 High Thrust Settings during Selected Test Cycle.

The test cycle you use (for example, accelerated severity cycle) may involve high thrust setting operation for durations that significantly exceed those of the engine flight cycle. If so, we may accept a field inspection interval longer than the IMI test length. This approach requires caution, because: • Some engine parts will wear as a function of time at load, rather than from low-cycle fatigue.

• Life extrapolation based on material property data alone is imprecise, at best.

Under these circumstances, you may need to draw supporting evidence from other: • Engine tests.

• Component tests.

• Subassembly tests.

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04/13/2016 AC 33.90-1A Using the Early ETOPS Test of § 33.201 to Demonstrate IMI Compliance. 2.1.7 2.1.7.1 General.

Section 33.90(b) allows you to use an approved test conducted per § 33.201, in lieu of a separate IMI test. Use of the Early ETOPs test allows you to demonstrate compliance with both regulations through a single test on one engine.

If you use this method, the following conditions apply: 1. After you complete the full number of test cycles required for an IMI test performed per § 33.90(a), you must interrupt the § 33.201 test to conduct a complete on-wing (or other) inspection. Note the following: a. The inspection must be acceptable to us, the FAA, in order to demonstrate compliance with § 33.90 requirements.

b. An acceptable on-wing inspection must include, but is not limited to, the inspections and tests listed in paragraph 2.1.7.2 of this AC.

2. Prior to EIS, you must complete the § 33.201 test in its entirety. This will provide further evidence that no undiscovered engine fault exists during the IMI portion of the test.

3. If the IMI inspection is completed and the TC is issued, you must complete the remaining portion of the § 33.201 test in order to comply with § 33.90(b) requirements.

4. FAA review of the general pass/fail criteria defined in paragraph 2.1.5 of this AC must demonstrate that the engine is fully serviceable per the ICAs, unless otherwise accepted by us.

2.1.7.2 On-Wing Inspection.

2.1.7.2.1 Borescope Inspection.

Full borescope-inspect all accessible gas path stages or areas of the fan, compressor, combustor, and turbine modules, to the serviceable limits of the ICAs.

2.1.7.2.2 System Fault and Status Message Interrogation.

Evaluate all system fault and status messages, for electronic-control- equipped engines. Include both current and previously recorded messages, to the serviceable limits of the ICAs.

2.1.7.2.3 Oil System Chip Detector and Filter Inspection.

Inspect all oil system chip detectors and filters for contaminants.

2.1.7.2.4 Fuel System Filter Inspection.

Inspect all fuel system filters for contaminants.

2-6 04/13/2016 AC 33.90-1A 2.1.7.2.5 Main Engine Oil Sample Test.

Test the engine oil (for example, spectrographic analysis) for contaminants that might indicate impending internal failure.

2.1.7.2.6 Visual Inspection.

Perform a complete visual inspection of the inlet, exhaust, and externals, to the serviceable limits of the ICAs. The engine must be serviceable.

2.1.7.2.7 Power Calibration.

Demonstrate that the engine can produce rated power or thrust at a sea-level, hot-day corner point condition within approved limits.

Fixed Engine Overhaul Period. 2.2 You may recommend a fixed overhaul period as the equivalent of an IMI , if you do not intend to cover the engine with a structured inspection program. If you use this approach, you should: • Conduct the engine test under § 33.90 in a similar manner to that described in paragraph 1.7 of this AC.

• Determine if the test results support the desired fixed overhaul period.

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04/13/2016 AC 33.90-1A Appendix A APPENDIX A. ADVISORY CIRCULAR FEEDBACK FORM A-1