The damage tolerance certification of friction stir weld (FSW) aircraft structure requires that consequence of cracks approaching welds be both understood & predictable. As part of Alcoa’s FSW development effort, a wide panel test program was conducted to characterize friction welded material tolerance to large-scale cracks, and predictability of same. Residual strength, fatigue crack growth, and residual stress profile measurements were made from 12 in. wide center-crack panel tests, possessing butt-weld seams at various distances and angles from the starting crack. The tested FSW panels consistently demonstrated fatigue crack growth and residual strength properties equal to or better than base metal panels tested without welds. Discrete cracks propagating toward and passing through friction welds in all cases displayed improved fatigue crack growth and/or tearing resistance over that of base metal. No significant crack turning events were observed, and in the case of dual crack fronts the panel failures consistently originated from the crack front furthest removed from the weld. The observed test results are shown to align well with fracture mechanics prediction principles, and interpretive findings are presented to offer FSW-induced residual stress and alteration of crack-tip plastic flow as plausible explanations for the observed FSW panel property improvements.