USAF damage tolerance design guidelines are specified in Joint Service Specification Guide JSSG-2006 [1998].  The guidelines apply to all safety of flight structure, i.e., structure whose failure could cause direct loss of the aircraft, or whose failure, if it remained undetected, could result in the loss of aircraft.  The guidelines stipulate that damage is assumed to exist in each element of new structure in a conservative fashion i.e., critical orientation with respect to stress field and in a region of highest stress.  The structure must successfully contain the growth of the initial assumed damage for a specified period of service, and must maintain a minimum level of residual static strength both during and at the end of this period.