The hydraulic high pressure return line to a B757-200 left hydraulic system ruptured during climbout allowing the system's fluid to escape. An emergency was declared with a return to the departure airport.

Narrative

During our initial climb passing 14;000 FT Captain (pilot flying) noticed the Left Hydraulic System Pressure EICAS message. I was acknowledging an ATC frequency change when he pointed out the EICAS message; shortly after we also received the Master Caution and numerous EICAS messages associated with the loss of the left hydraulic system. Captain then instructed me to tell Center that we will be returning to our departure airport. Captain then assumed communication responsibilities; declared an emergency; and received clearance back. The flight attendants were notified that we will be returning and that we would contact them in a few minutes and brief them. After reviewing all the indications related to this malfunction we concluded that we had a loss of the left system hydraulic quantity (.12 RF Indicated on EICAS status page). We also noticed that we still had system pressure of approximately 300 psi. We immediately consulted the QRH and followed the checklist procedures for L; C; or R Hydraulic Quantity; and L; C; or R Hydraulic System Pressure for 757; if L system only inoperative. We also reviewed the When Alternate Flap Operation is required and the When Alternate Gear Extension is required procedures at the end of the checklist. Captain requested a long final and advised Tower that we will be remaining on the Runway to have our gear pinned. Since we still have system pressure available we decided to configure early and verify normal operations of the Gear and Flaps. Once we verified that we had normal operation of the Gear and Flaps we reviewed the Overweight Landing procedure; reviewed the list of possible inoperative system; and accomplished normal checklists in preparation for landing. Captain briefed the flight attendants and we contacted Operations (we were not able to contact Dispatch at this time) and advised them that we will be returning and that we will be requesting that maintenance pin our gear. Approach and landing were uneventful with an Overweight Landing weight of 214;000 LBS. Landing was very smooth at a speed of 150 KIAS and 100 foot rate of descent. ARFF command contacted us on the runway and we requested that they examine the left side of our aircraft and in particular the area by our left engine. No leak was noted at this time. Maintenance arrived and pinned our gear. We taxied to gate. Upon maintenance inspection of the left engine pylon a hydraulic return line was found to be ruptured (1 inch high pressure return line) and all the hydraulic leaked into the engine pylon. The logbook was completed with all discrepancies noted including the overweight landing.