What was found
THE ACCESSORY GEARBOX MAIN DRIVESHAFT HAD FRACTURED. THE REPORTED IN-FLIGHT SHUTDOWN WAS A RESULT FROM FRACTURE OF THE ACCESSORY GEARBOX MAIN SHAFT DRIVE BEVEL GEAR DUE TO FATIGUE INITIATING AT A GEAR TOOTH RADIUS. THE FRACTURED GEAR CAUSED MECHANICAL DAMAGE TO ITS MATING INPUT GEAR TEETH AND GOUGED BOTH THE GEARBOX HOUSING AND ITS COVER. TO ALLEVIATE THIS CONDITION, A GEAR FEATURING AN INCREASED MATERIAL THICKNESS AT THE GEAR WEB WAS INTRODUCED INITIALLY BY SB 7152 (2-80), SUPERSEDED BY SB 7258 (6-87), THEN BY SB 7269 (3-88) FEATURING GEARS MANUFACTURED FROM SUPERIOR MATERIAL AND ACCOMMODATING LARGER BACK LASH.