Purpose. This advisory circular (AC) describes an acceptable method, but not the only method, to support certain comparative assessment compliance findings to Title 14 of the Code of Federal Regulations (14 CFR) part 33, § 33.15, Materials, for turbine engine projects. Comparative assessment of certain data is often necessary to show the required functional and durability equivalencies between engine combustor and turbine section parts from different design or manufacturing processes, e.g., parts manufacturer approvals (PMA) versus type design parts. These equivalencies relate to oxidation, hot corrosion, and thermal fatigue and erosion characteristics in the engine environment. This data is necessary to support overall FAA design approval of turbine engine and auxiliary power unit (APU) parts approved under PMA, type certificate (TC) design change, supplemental type certificate (STC), or repair or alteration authority.

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