What was found
DURING AAIP A1660 600 HR SCHEDULED INSPECTION, IT WAS DISCOVERED THAT THE FWD ENG FIREWALL HAD A TOTAL OF 5 CRACKS IN 4 LOCATIONS. TWO OF THE LOCATIONS ARE ON THE UPPER LT & RT BEND ADJACENT TO THE END OF THE ENG COWLING HINGE CONSISTING OF 1 CRACK EACH APPROX 1 INCH IN LENGTH. THE OTHER TWO LOCATIONS ARE ON THE AFT SIDE OF THE FIREWALL MIDWAY DOWN ON THE LT & RT SIDE JUST AS THE FIREWALL BENDS & CHANGES ANGLE. THESE LOCATIONS CONSIST OF 1 CRACK APPROX 5 INCH IN LENGTH ON THE DOUBLER & UNKNOWN LENGTH CRACK UNDERNEATH THE DOUBLER. THE LAST CRACK LENGTH UNKNOWN IS IN THE SAME LOCATION, OPPOSITE SIDE UNDERNEATH DOUBLER. A REPLACEMENT FIREWALL HAS BEEN ORDERED.