B767 flight crew reported hydraulic system anomaly in flight. The flight crew diverted and landed safely. Maintenance inspection found an engine pylon bent open due to failure of a fastener.
Synopsis
B767 flight crew reported hydraulic system anomaly in flight. The flight crew diverted and landed safely. Maintenance inspection found an engine pylon bent open due to failure of a fastener.
Narrative
I had been in the crew rest seat for approximately 1 hour when my break was interrupted by one of the flight attendants. He let me know that the Captain was requesting me to return to the flight deck. I gathered my things and headed back in to the flight deck; and was briefed by the Captain about the situation. The L HYD QTY EICAS message was displayed on the top screen; while the bottom screen was on the status page; showing the left hydraulic quantity reading of 0.0 RF. The Captain was the Pilot Flying; and he directed us to execute the non-normal checklist for L HYD QTY. Before we were able to start the checklist; the left autopilot disengaged. The Captain transferred controls to the flying seat first officer and we reengaged the right autopilot. At this point the Captain began attempting to contact dispatch and Maintenance Control while the other FO and I executed the checklist. The left hydraulic pressure remained at 3120 psi. We turned off the electric and demand pumps as directed while the Captain was talking to dispatch and Maintenance Control. Once we turned off the pumps; the left hydraulic pressure dropped to 0.We were able to speak with dispatch fairly easily; but the patch with Maintenance Control was nearly unreadable on the first attempt. Once the Captain and dispatcher agreed to divert back to ZZZ; we obtained a clearance from ATC and began the 180 degree turn; at which point we lost contact with dispatch. Once out of the turn we were able to reestablish contact with dispatch and subsequently had Maintenance Control patched back in. Maintenance Control recommended that we could try turning the pumps back on; or we could leave them off and turn them back on just prior to landing in order to have full hydraulic capabilities during the landing process. We turned the pumps back on; at which point the left hydraulic quantity indicator showed approximately 0.84; and the pressure indicated ~3120. We left the pumps on for the remainder of the flight; all indications were normal for the remainder of the flight; and we landed uneventfully back at ZZZ.After landing; maintenance personnel arrived at the flight deck and began asking us some questions about what exactly happened and what were our instrument indications when this was all happening. They then showed us a picture of a panel on the left engine pylon that was bent open; telling us that the hydraulic sensors are right behind that access panel and that could have been the cause of our issues. This panel was not bent open during my walkaround (I diligently check the pylons during every preflight walkaround); and the mechanics indicated that the fastener that normally holds it closed is weak and prone to failure. At that point we completed our checklists and departed the aircraft.
Second reporter narrative
Level in cruise about an hour and half into cruise L HYD QTY EICAS illuminated. FO began reading checklist notes. We decided to call up the Relief Pilot due the nature of the issue. While the Relief Pilot was coming up the left autopilot disconnected. Once the Relief Pilot was seated; the FO completed the checklist for L HYD QTY which has us shut off the demand and primary to the left side. Used the call me function to patch in with dispatch and Maintenance Control to discuss the issue. There was a history of the hydraulic qty reading issue on the aircraft; but we all agreed (CA; FO; Relief Pilot; Dispatch; Maintenance Control) that the fact the auto pilot disconnected prior to turning off the hydraulic switches was a cause for concern to not continue into ETOPS airspace. While on the phone patch with Maintenance Control the hydraulic qty went back to normal; so we decided to turn the hydraulic pumps back on; seeing that there was an indication problem; though still concerned with the autopilot kicking off; we monitored the situation back to ZZZ. Landed overweight after completing all appropriate checklists.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.