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The Role of Nondestructive Testing in
Aircraft Damage Tolerance

Table 1

Table 1 Initial size assumptions for primary discontinuities
Category	Critical Detail	Intitial Discontinuity Size Assumption*
Slow crack growth and fail safe primary element	holes, cutouts and so on	for thickness ≤ 1.3 mm (0.05 in.); through thickness  with ci = 1.3 mm (0.05 in.)
		for thickness > 1.3 mm (0.05 in.); quarter circular corner with ci = 1.3 mm (0.05 in.)
	other	for thickness ≤ 3.2 mm (0.125 in.); through thickness  with 2ci = 6.4 mm (0.25 in.)
		for thickness > 3.2 mm (0.125 in.); semicircular thickness  with ci = 3.2 mm (0.125 in.)
	components with embedded discontinuities	to be determined based on NDT capability
	welded componentst	to be determined based on NDT capability
Fail safe multimode path (adjacent structure)	holes, cutouts and so on	for thickness ≤ 1.3 mm (0.05 in.); through thickness  with ci = 0.05 + Δc±
		for thickness > 1.3 mm (0.05 in.); quarter circular corner with ci = 0.05 + Δc±
	other	for thickness ≤ 3.2 mm (0.125 in.); through thickness  with 2ci = 0.25 + 2Δc±
		for thickness > 3.2 mm (0.125 in.); semicircular surface  with ci = 0.125 + Δc±
Fail safe crack arrest (adjacent structure)	skin stringer or skin frame	ci extends across two panels (bays); central stringer (frame) broken
	skin stringer or skin frame with tear straps	ci extends between tear straps (bays); central stringer (frame) broken
	holes, cutouts and so on other	quarter circular corner with ci=0.005 + Δc± semicircular surface  with ci = 0.01 + Δc±
* discontinuity oriented in most critical direction t discontinuity assumed in both weld material and in heat affected zone of parent material ± Δc is the growth of the indicated discontinuity between time that part enters service and time of primary element failure

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