Standard Practice for Determining Safe-Life, Inspection Threshold and Recurring Inspection Intervals

Importancia y uso:

4.1 This practice provides one means for determining the scatter factors to establish either the safe-life, or inspection threshold, or recurring inspection intervals, or combinations thereof, as a result of aeroplane durability and damage tolerance assessments. This information can be used in conjunction with Specification F3115/F3115M.

4.1.1 This practice defines scatter factors or factors to be used on the unfactored test or analytical mean lives, or both, for determining factored lives (that is, safe-life, inspection threshold, or recurring inspection intervals, or combinations thereof). These factors may be related to but are different from other factors such as load enhancement factor, and life factor that are used to compensate for long test duration. For guidance on life and load enhancement factors, refer to DOT/FAA/AR-10/6 or from relevant CAAs.

4.1.2 The unfactored test or analytical mean life, or both, must be determined prior to the usage of this standard practice (see 4.5.1).

4.2 The material presented herein is derived from the references listed in Section 2.

4.3 Either the safe-life or inspection thresholds can be determined for the entire aeroplane or separately for components such as wing, empennage, landing gear, control surfaces, etc. Such determinations are based on test(s), similarity to previous test(s), or analysis supported by tests. Recurring inspection intervals are typically determined on the same basis but may also be supported by in-service data.

4.4 The scatter factors described in this practice are applicable to cyclic test data that meets the following criteria:

4.4.1 The cyclic test article must be representative of the production article. Careful consideration must be given for any modifications or alterations, or both, made to the test article prior to or during testing, or both, for metallic structures.

4.4.2 At the completion of full-scale or component fatigue/cyclic tests (excluding landing gear), the residual strength capability must be demonstrated before determining either the safe-life, or inspection threshold.

4.5 The following are not within the scope of this standard:

4.5.1 Methodologies of durability, damage tolerance analysis, or test, or combinations thereof.

4.5.2 Structures which use novel fabrication methods such as friction stir welding, additive manufacturing, and thermoplastic welding.

4.5.3 Structural bonding (except already proven metal-to-metal bonding, etc.); for guidance on structural bonding refer to AC 20-107B (or AMC 20-29).

4.6 The Finite Element Model (FEM) used for analysis must be validated with test data, or other independent analysis methods in accordance with relevant CAA requirements.

4.7 The inspection intervals determined using this practice are independent of other inspection intervals that are defined by other process, such as Maintenance Steering Group (MSG).

Subcomité:

F44.30

Referida por:

F3720_F3720M-24

Volúmen:

15.09

Número ICS:

49.020 (Aircraft and space vehicles in general)

Palabras clave:

damage tolerance; fatigue; inspection; life-limit; safe-life; scatter factor; threshold;