What was found
LT PRIMARY HEAT EXCHANGER DIFFUSER/PLENUM ASSY CRACKED. ACFT GROUNDED. ACCOMPLISHED EA 800-21EA-13765 "LT PLENUM DIFFUSER CUTOUT DAMAGE TEMP REPAIR", STEPS 1 THRU 6. INSTALLED REPAIR DOUBLER AFT END LT CUTOUT OF DIFFUSER PLENUM. INSPECT THE NUTPLATE AND DOUBLERS FOR SECURITY EVERY 500 FLIGHT HOURS. IF FURTHER DAMAGE IS NOTED CONTACT AOG ENGINEERING FOR EVALUATION. AT NEXT HEAVY MAINTENANCE CHECK, REMOVE TEMP REPAIR AND ACCOMPLISH A PERMANENT REPAIR ON THE PLENUM. ON DEFERRAL.