What was found
PDIS 108 73-35 4592 13FEB19 CAN OPEN U LOGPAGES:2612304 L ENGINE FUEL FILTER EICAS MESSAGE CAME ON DURING CLIMB. EICAS MESSAGE CAME ON AND OFF SEVERAL TIMES AND REMAINED ON THROUGHOUT. MOST OFF THE FLIGHT. LEFT ENGINE VIBRATED AND VIBRATION INCREASED DURING DESCENT COUPLIED WITH NON-NORMAL AND NORMAL CHECKLISTS DECLARED AN EMERGENCY AND RETURNED TO CAN. PER FIM 73-11-00-1, REMOVED LH ENG FUEL FILTER ELEMENT PER AMM 73-11-02-6, FILTER ELEMENT CHECKED NORMAL, NO CONTAMINATION. REPLACED FUEL FILTER DIFFERENTIAL PRESSURE SWITCH. ENG RAN AS PER JRH ,ALL PARAMETERS NORMAL.