The second example is academic, but illustrative.  It is a multiple load path dependent beam consisting of members A, B, C (Figure 6.2.2a).  Assume that crack 1 is the critical crack.  (If the critical location was at the other side of the hole, damage development would be similar as in Figure 6.2.2).  Due to assembly drilling the two members, A and B should both be assumed flawed.  The damage development is shown in Figure 6.2.2b, c.

Figure 6.2.2.  Damage Development in Multiple Load Path, Fail Safe Structure

Cracks 1 and 2 both start as 0.05 inch flaws.  Crack 1 is assumed to grow faster, and when K = K_Ic rapid crack propagation (instability) will occur at which point member A is assumed failed.  Remaining structure damage has to be assumed in the adjacent member (crack in member C).  It is a 0.005 inch crack plus its prior growth, Da.

Due to member failure the stress-intensity factors of all cracks will show a jump.  Therefore, cracks 2 and 3 will grow much faster than before:  Final failure will occur when the stress-intensity factor (K) of crack 3 reaches K_Ic, or when K of crack 2 reaches K_c, whichever occurs first.  (It is assumed that plane stress prevails in the thin member B).  The period between failure of member A and final failure (indicated by t in Figure 6.2.2c) has to be adequate for one of the options of remaining structure damage inspection.  Otherwise, the structure would not qualify as Multiple Load Path, Fail Safe structure.