What was found
(CAN) ON APPROACH, FLAPS WERE SELECTED TO 30 DEGREES. FLAP INDICATION WAS SHOWING 20 DEGREES & AIRSPEED CONFIRMED FLAPS WERE INOPERATIVE. FLAP MOTOR CIRCUIT BREAKER WAS POPPED & STANDBY FLAP MOTOR WAS TRIED WITH NO RESULTS. A SUCCESSFUL LANDING WAS MADE & FLAPS WERE FOUND STUCK IN THE 20 DEGREE POSITION. INSPECTION REVEALED FLAP ACTUATOR SUPPORT ASSY TORN & CRACKED. TRANSMISSION HAD TWISTED SUPPORT ASSY & JAMMED. ATTEMPTED USE OF ALTERNATE FLAP MOTOR BY CREW HAD SHEARED DRIVE COUPLING. MM CALLS UP AN INSPECTION OF FLAP SUPPORT ASSY EACH 400 HRS. SUPPORT ASSY APPEARED TO HAVE NUMEROUS CRACKS PRESENT PRIOR TO BREAKING POINT, LEADING TO INCREASED STRESS & UNSUPPORTABLE LOAD.