The margins of safety on flange crushing are calculated with the following equations,
where 𝜎𝜎 𝑏𝑏𝑏𝑏 is the maximum compressive stress that occurs under the head or nut for either the Ftot or FA (refer to Table 7-3 for applicable fastener load criteria). Note that considering bearing stresses allowables is rather conservative. (It is known that for some ductile metallic materials a bearing stress up to twice the yield limit of the flange material does not result in flange indentation).
However, in case the margins of safety are low and a simple approximation cannot be accepted, such as for honeycomb crushing, it is advised to determine the crushing allowable by test (see, for example, the ECSS-E-HB-32-22).