Investigation focuses on cracked engine mount components that went undetected during maintenance on the 34-year-old MD-11.

The UPS plane crashed in Louisville, Ky., in November shortly after takeoff, when the left engine flew off the wing. Fifteen people were killed.

Boeing (BA) had flagged past failures of a structural component later found cracked on the cargo jet involved in November’s fatal United Parcel Service (UPS) crash, according to a mid-investigation update from U.