What was found
ON TAKEOFF, AIRCRAFT SUFFERED A BIRDSTRIKE TO THE LT ENGINE WHICH PRODUCED INCREASED N1 VIBRATION. THE FLIGHT CREW ELECTED TO RETURN AND NOTIFIED ATC. AN OTHERWISE NORMAL APPROACH AND LANDING WAS MADE. MAINTENANCE INSPECTED THE ENGINE AND FOUND TWO DAMAGED FAN BLADES. THESE BLADES AND THEIR BALANCED MATE WERE REPLACED AND A GROUND RUN WAS PERFORMED. VIBRATION INDICATION WAS NORMAL AND THE AIRCRAFT WAS RELEASED FOR SERVICE.