All aircrafts are designed to withstand the normal flight and landing loads expected during a typical flight cycle. These loads will include the normal manoeuvres the aircraft is expected to make. The designer will build in a safety factor, to compensate for loads slightly larger than normal. Sometimes extreme circumstances occur, which cause stresses outside the normal design limits.
If the design limits are exceeded, then damage may occur to the aircraft. If it is known or suspected that the aircraft has been subjected to excessive loads, then an inspection should be made, to ascertain the nature of any damage that may have occurred. The manufacturer will normally have anticipated the nature of some of these occurrences and detailed special checks for these ‘Abnormal Occurrences’.