What was found
IN CRUISE AT FL370 LEFT ENGINE FAN VIB INDICATIONS RANGED ERRATICALLY FROM 0.4-5.0 FOR APPROXIMATELY THREE MINUTES. NO ACTUAL VIBRATION FELT. TRANSFERRED TO MDDR 136585 MEL 77-31-01, CAT C DUE DATE 01NOV20. RS 2107Z 25OCT, ILN MX. REMOVED AND REPLACED ENGINE VIBE MONITOR, IAW AMM 77-31-03 (OFF PART: PN 241-256-000-131, SN EF480). OPERATIONS CHECK GOOD. THIS CLEARS DMI NR 136585 Y.I.- RS 0137Z. IN FLIGHT FAN VIB INDICATOR ERRATIC INDICATIONS FROM .6 -5. REOPENED MDDR 136585, IAW DDG 77-31-01. MX ACTION COMPLIED WITH. PLACARD NSTALLED. MCC NOTIFIED YK 1430Z. REMOVED AND REPLACED CONNECTOR D10994, IAW SWPM 20-60-00. OPERATIONS CHECK GOOD, IAW AMM 77-31-00. T/I BA 1621Z.