ED Decision 2003/18/RM
(a) Design properties may be used subject to the following conditions:
(1) Where applied loads are eventually distributed through a single member within an assembly, the failure of which would result in the loss of the structural integrity of the component involved, the guaranteed minimum design mechanical properties (‘A’ values) must be met.
(2) Redundant structures, in which the failure of the individual elements would result in applied loads being safely distributed to other load carrying members, may be designed on the basis of the ‘90% probability (‘B’ values)’.
(3) ‘A’ and ‘B’ values are defined as follows:
(i) An ‘A’ is a value above which at least 99% of the population of values is expected to fall with a confidence of 95%.
(ii) A ‘B’ value is a value above which at least 90% of the population of values is expected to fall with a confidence of 95%.
(b) Design values greater than the guaranteed minimums required by sub-paragraph (a) of this paragraph may be used if a ‘premium selection’ of the material is made in which a specimen of each individual item is tested before use to determine that the actual strength properties of that particular item will equal or exceed those used in design.
(c) Material correction factors for structural items such as sheets, sheet-stringer combinations, and riveted joints, may be omitted if sufficient test data are obtained to allow a probability analysis showing that 90% or more of the elements will equal or exceed allowable selected design values.
EASA Very Light Aeroplane (VLA) Design: Structural integrity relies on material properties. Single load-path components require guaranteed minimum ('A' values) strength. Redundant structures can use 'B' values (90% probability). Premium material selection allows higher design values based on individual item testing. Statistical analysis can justify omitting material correction factors.
* Summary by Aviation.Bot - Always consult the original document for the most accurate information.
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