B747 Undifferentiated or Other Model
Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Provided Assistance; Flight Crew Landed As Precaution; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Overcame Equipment Problem; Flight Crew Diverted; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft; Company Policy
Suspected  #4 Hydraulic Leak Divert to ZZZZ1Departed ZZZ enroute to ZZZZ. Several hours enroute we noticed #4 hydraulic system indicated abnormally low quantity at approximately .45.We continued to monitor and noticed a .01 decrease per approx every 30 to 45 minutes. Over [geographic area 1] as we neared [geographic area 2] we became concerned that we did indeed have a slow hydraulic leak as we were now indicating .39.We preempted the 'hyd quantity low 4' QRH procedure in hopes that depressurizing system 4 pumps would slow or prevent our suspected leak given we still had nearly 6 hours to destination. If the current trend continued we would have faced a possible loss of system 4 resulting in degraded flight controls and manual gear extension at destination.After depressurizing system 4 the downward trend in hydraulic quantity continued. Shortly after our coast out point of ZZZZZ I made the decision to advise company operations and ATC of our situation and made arrangements for us to divert to our planned enroute alternate of ZZZZ1.We repressurized system 4 prior to landing as per the QRH and landed without further incident at ZZZZ1.Plan more ground time to address trending maintenance items on a more regular schedule to strike a balance with the demanding flight schedule as hydraulic issues are appearing more regularly and have been documented in recent logbook discrepancies with this particular aircraft.
Captain reported diverting due to #4 hydraulic system losing quantity.