What was found
(CAN) DURING VISUAL INSPECTION OF MAIN ROTOR SYS PRIOR TO ACFT DEPARTURE. THE ENGINEER WAS TAKING A VISUAL LOOK DOWN THE LENGTH OF THE BLADES WHILE STANDING ON THE MX STEP. DUE TO THE ANGLE OF THE SUN ON THE ROTOR BLADES, NOTICED A STRANGE SHADOW ON THE UPPER SURFACE OF THE BLUE BLADE. UPON FURTHER INSPECTION OF THE BLUE MAIN ROTOR BLADE, IT WAS DISCOVERED THAT THE L/E STRIP HAD COME COMPLETELY DEBONDED ON THE UPPER SURFACE. THE DEBONDING RUNS THE COMPLETE LENGTH OF THE STRIP`S UPPER SURFACE. THE DEBONDING ACTUALLY HAS STARTED TO LIFT THE TAPE THAT COVERS THE SCARF JOINTS. ACFT WAS RETURNED TO THE HANGAR AND ALL 4 ROTOR BLADES WERE REPLACED.