What was found
(CAN) ROUTINE INSPECTION FOUND CRACKS IN LEFT NOSE RIB AT STATION 100.00 OF WING. THE RIB WAS CRACKED THROUGH LIGHTENING HOLE TO UPPER BEND RELIEF. RIGHT SIDE AT 100.00 WAS ALSO SHOWING CRACKS FROM RIVET HOLES AND FROM THE BEND RELIEF TOWARD THE LIGHTENING HOLE.BOTH RIBS WERE REPLACED. NO OTHER RIBS AFFECT ED. PLANE BELONGS TO A FLYING SCHOOL WHERE OUT OF THE 7 OPERATED 4 SHOWED SIGNS OF CRACKS ON BOTH OREITHER SIDE.TIME ON AIRCRAFT RANGE FROM 9500 TO 16746.1 HRS.