B767 flight crew reported low hydraulic fluid level in center system and suspected leak during cruise. Flight crew returned to departure airport as fluid level continued to decrease and landed safely.
Synopsis
B767 flight crew reported low hydraulic fluid level in center system and suspected leak during cruise. Flight crew returned to departure airport as fluid level continued to decrease and landed safely.
Narrative
About 30 minutes after we leveled off in cruise; we got a C HYD QTY EICAS message. C Hydraulic quantity was at .49. We followed the Non-Normal checklist; which instructed us to turn off all Center Hydraulic tank pumps. When they were shut down; we had .48 remaining C HYD Quantity. At the direction of the C HYD QTY checklist; we reviewed the HYD SYS PRESS - C (Only) checklist to see the list of Inoperative items (And really--there should be a hyperlink to it!). We switched to the Left Autopilot and changed the transponder to the L position. I called the Flight Attendants; spoke with Person A and told her to please wake up the Relief Pilot and tell him we needed him on the flight deck. I told her we had a hydraulic problem and would not be continuing to ZZZZ1; but didn't have a new plan as of yet. I told her to have the Purser call me.When the Relief Pilot returned to the flight deck; he reported the FAs in the back of the aircraft smelled an acrid/burning odor right at takeoff; so pungent it made a couple of them feel ill. This information helped us come to the conclusion we did indeed have a hydraulic leak as opposed to an indication error.We contacted Dispatch and conferred with Maintenance Control. Maintenance Control told us the smell reported by the FAs was consistent with hydraulic fluid getting into the air conditioning system. We all agreed continuing to ZZZZ1 was not an option. The Dispatcher; after conferring with the Company Communications System; told us a return to ZZZ was what they wanted. Since ZZZ had long runways and good weather and a proclivity for long; straight-in final approaches; it was already one of our choices for a diversion airport; along with ZZZ1; or possibly ZZZ2; so we agreed.We [requested priority handling] with ZZZZ center. I spoke with the Purser and told her we would be returning to ZZZ with a hydraulic problem and to please inform her crew. Then I made an announcement to the passengers and afterwards we began our turn back to ZZZ. Dispatch provided us with normal landing data for Runway XXC; XXR and YYC; and non-normal landing distance (7400ft). We said we would prefer Runway YYC as it was longer and not in use per the ATIS; so there would be no issues with traffic behind us.After discussing the hydraulic leak and the possibility of hydraulic fluid on the gear and the potential for a fire with hot brakes (an overweight landing was planned--center tank fuel was depleted; so dumping fuel was no longer an option) I told the Purser I wanted them to prep for an evacuation. I told her to tell the members of her crew first; and then to call me back when that was complete; so I could make an announcement to the passengers. However; she began making the required Preparation for Evacuation PA announcement before I could talk to the passengers myself. I interrupted her PA and explained that while I believed we would have a normal approach and landing; it was only with an abundance of caution I wanted this preparation to take place. Anticipating a possible loss of C Hydraulic Pressure; we reviewed the HYD SYS PRESS C (Only) checklist and went over possible scenarios of what might happen when we started configuring and what we would do if we got the low-pressure light at certain stages of configuration. (e.g. Go around and perform the HYD SYS PRESS checklist; which requires alternate flap and gear extension; continue to landing if we were at flaps 20 and gear down; etc.) Center Hydraulic Quantity had dropped to about .42 by this time.We told ATC to plan on us being on the runway for a while; anticipating the possible loss of Nosewheel Steering and to have ARFF standing by. Once level at 9000 feet; we depressurized the cabin as per the Evacuation Preparation checklist.We had flown direct to ZZZ the entire way from ZZZZ airspace in an effort to land with as much center hydraulic fluid as possible. ZZZ Center slowed us to 210 knots on a dog leg base to final for the ILS YYC. We turned on the C Hydraulic pumps as per the checklist's Deferred Items; to extend the flaps. At flaps 5; the fluid dropped to about .24. ATC slowed us to 170 and I (now the Pilot Flying) asked for flaps 20 on schedule. I dropped the gear around ZZZZZ.So; we were at flaps 20 and gear down; established on the ILS when the C HYD PRESS EICAS came on. We elected to remain at flaps 20 for the landing; to avoid possibly draining the rest of C Hydraulic fluid or complicating a possible go-around. HYD C fluid was at approximately .18 now.We landed overweight (#330;000) flaps 20. Landing was uneventful and we rolled out; stopping straight ahead. ARFF met the aircraft and reported some steam from the right main gear; but no fire. (Highest brake temp was 4.) We requested a tow to the gate; out of concern for a loss of Reserve Brake and Steering fluid and therefore Nosewheel Steering at an inopportune time. Maintenance met the aircraft and a tug was called. Maintenance had us run some checks of the brakes (I had to pump them on and off several times.) The tug left and then Maintenance said since we had brakes; we were to taxi to the gate. I told him we didn't have Nosewheel Steering. (Although we were aware we did have the below the standpipe hydraulic fluid; after reviewing the system earlier; and not knowing where the leak was; we decided not to risk relying on the Reserve Brake and Steering System; a possible failure of which would leave us with only Accumulator brakes.) Another tug showed up and we were brought to the gate.
Second reporter narrative
Around one hour into the flight; while with ZZZZ center; the HYD QTY C EICAS message illuminated. At that point we accomplished the HYD QTY C non normal checklist. Upon completion of the checklist; which turns off the center pumps to isolate fluid; there was approximately 45% quantity in the center system. The checklist also referred us to the HYD PRESS C checklist to identify inoperative equipment with the system pumps off. Based on the effected equipment we selected from the right to the left autopilot. We also reviewed the HYD PRESS C checklist to identify contingencies in case system pressure was lost upon restoring the center pumps. At this point the Captain woke the Relief Pilot from break and then advised dispatch. We discussed whether a diversion was appropriate. Neither of us were comfortable with continuing; especially in the event that a diversion to an ETOPS alternate might be required with a compromised hydraulic system. We also preferred a diversion airport with long runways. ZZZ and ZZZ1 were discussed as our preferred airports with ZZZ2 as a third option. In consultation with dispatch and Maintenance Control the decision was made to return to ZZZ. An [priority handling] was also requested with ZZZZ Center.When the Relief Pilot returned to the flight deck he advised us that the flight attendants advised him of an acidic smell on takeoff. We suspected the smell was a result of the hydraulic leak. This led us to discuss the possibility of a potential fire scenario upon landing from fluid leaking on hot brakes. We also discussed possible contingencies in the event we were not able to fully configure the aircraft prior to losing center system quantity/pressure. It was decided to restore the pumps and configure the aircraft just prior to glideslope intercept at around 5000 to 7000 ft to give us time to level off and complete the HYD PRESS C checklist in the event it became necessary. We also made the decision to prep the cabin for evacuation as a precaution; in the event of fire; a loss of brakes/nosewheel steering; or landing in an unusual configuration. We also advised dispatch that we preferred to land on Runway YYC due to the longer length and desired crash fire rescue. It took approximately 90 minutes to return to ZZZ due to strong headwinds. This gave ample time to discuss contingencies and allowed the flight attendants plenty of time to prepare the cabin. After descending below 10;000 ft we finished the preparation for evacuation checklist and upon reaching 7000 ft we restored the C system pumps and began configuring the aircraft. We were able to configure to gear down and flaps 20 prior to losing pressure in the center hydraulic system. At this point the quantity was approximately 12%. We also received the SPOILERS EICAS message (as anticipated) and briefly reviewed the associated checklist. The approach was normal and stable; well flown by the Captain; and the landing uneventful. Given concerns over nose wheel steering the decision was made to stop straight ahead on the runway. Given concerns over low system quantity/pressure impacting nose wheel steering a tow in to the gate was called for. Crash fire rescue examined the landing gear area. There was some steam from hydraulic fluid on warm brakes; but no indication of fire or excessive temperatures. The aircraft was subsequently towed to the gate and the passengers deplaned to another waiting aircraft to resume their flight. We debriefed as a crew and then contacted the Chief Pilot per the FOM. At this point we were timed out and released from further duty. I generally thought we worked together as a crew; and the Captain did an excellent job managing the situation.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.