What was found
(CAN) SHORTLY AFTER TAKEOFF, ABOUT 400 FT ABOVE GROUND, A/C SOUND & VIBRATION LEVELS SUDDENLY CHANGED FROM NORMAL TO HEAVY VIBRATION THROUGHOUT WHOLE A/C WITH OSCILLATING, DRONING NOSIE. AS WELL, PILOT NOTICED PULSING FEEDBACK SE NSATION FROM ANTITORQUE PEDALS. PILOT IMMEDIATELY ABORTED CLIMB&CARRIED OUT PRECAUTIONARY DESCENT&NORMAL LDG W/O INCID.. TAIL ROTOR CNTL AUTH NEVER LOST. AFTER ENGINE SHUTDOWN, INSP REVEALED COMPLETELY FAILED FWD FAN SHAFT BEARING WITH DISINTIGRATED BEARING CAGES & BALLS EJECTED INTO IMPELLER. ANCILLARY DAMAGE TO IMPELLER, SHAFT&OIL COOLER BLOWER HOUSING. THER HAVE BEEN OTHER FAILURES OF TYPE ON BELL 407 RES ULTING IN TC AD CF-2000-02 REQ