What was found
THE AIRCRAFT EXPERIENCED A MAIN GEARBOX CHIP LIGHT IN-FLIGHT. INITIAL INVESTIGATION BY MAINTENANCE REVEALED THE CHIP DETECTOR HAD PICKED UP A SHEARED BOLT/NUT COMBINATION. FURTHER EXAMINATION OF THE GEARBOX WITH A BORESCOPE REVEALED THE UPPER WEB ON THE SPUR GEAR ASSY WAS CRACKED. THERE ALSO WERE 4 BOLTS MISSING THAT SECURE THE WEB TO THE SHAFT OF THE SPUR GEAR ASSY. THIS IS THE SECOND FAILURE OF THIS TYPE WITH THIS OPERATOR. AN EXAMINATION OF THE GEARBOX AT THE OPERATOR'S MAINTENANCE FACILITY IS BEING CORRDINATED WITH THE MANUFACTURER AND THE FAA BOSTON AIRCRAFT CERTIFICATION OFFICE.