Narrative:

The paperwork showed that the aircraft had lost hydraulic fluid on the flight and the flight crew documented that the center hydraulic system needed to be refilled; which is not a normal occurrence. Maintenance action simply refilled the fluid; without determining a potential cause. We noted that the hydraulic fluid was refilled; but decided to take the aircraft. At cruise; we noted a slow and steady decrease in the center hydraulic fluid level; but not to unsafe levels. After completing the ETOPS segment; I went back for my break (third break) and the fluid was still at approximately 60%; which is lower than normal but did not require any non-normal procedures. I went on my rest break; and was awaken about 10 minutes earlier than the scheduled break. When I arrived back in the cockpit; we had approximately 1 hour until landing; and the captain and the international relief officer (international relief officer) had completed the initial steps for central hydraulic low fluid; which called for turning off all of the center hydraulic pumps; which had some associated degradation in various flight control systems. I was briefed on the ramifications of the malfunction; resumed flying duties; and we completed the checklist to include turning on the pumps just before configuring the airplane with normal flap and gear extension. The crew had previously [advised ATC] before I returned to the cockpit. When we lowered the gear with the gear handle; the hydraulic level went all the way to 0; but the gear did lower without using the alternate systems. I flew an uneventful 20 degree flap landing; and we taxied clear of the runway. We had previously coordinated with ATC and the company to have the aircraft towed in; so we shut down the airplane after clearing the runway; and was towed in without incident.

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Original NASA ASRS Text

Title: B767 First Officer reported that they departed after the hydraulic system was serviced and the indication went to '0' prior to landing at the destination airport.

Narrative: The paperwork showed that the aircraft had lost hydraulic fluid on the flight and the flight crew documented that the center hydraulic system needed to be refilled; which is not a normal occurrence. Maintenance action simply refilled the fluid; without determining a potential cause. We noted that the hydraulic fluid was refilled; but decided to take the aircraft. At cruise; we noted a slow and steady decrease in the center hydraulic fluid level; but not to unsafe levels. After completing the ETOPS segment; I went back for my break (third break) and the fluid was still at approximately 60%; which is lower than normal but did not require any non-normal procedures. I went on my rest break; and was awaken about 10 minutes earlier than the scheduled break. When I arrived back in the cockpit; we had approximately 1 hour until landing; and the Captain and the IRO (International Relief Officer) had completed the initial steps for central hydraulic low fluid; which called for turning off all of the center hydraulic pumps; which had some associated degradation in various flight control systems. I was briefed on the ramifications of the malfunction; resumed flying duties; and we completed the checklist to include turning on the pumps just before configuring the airplane with normal flap and gear extension. The crew had previously [advised ATC] before I returned to the cockpit. When we lowered the gear with the gear handle; the hydraulic level went all the way to 0; but the gear did lower without using the alternate systems. I flew an uneventful 20 degree flap landing; and we taxied clear of the runway. We had previously coordinated with ATC and the company to have the aircraft towed in; so we shut down the airplane after clearing the runway; and was towed in without incident.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.