A B757-200 IN CLB AT FL190 DIVERTED DUE TO LOSS OF L HYD SYS PRESSURE AND QUANTITY. CAUSED BY A FAILED PRESSURE LINE ON THE L MAIN LNDG GEAR.

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DURING CLB; EICAS ANNUNCIATED 'L HYD QUANTITY' WITH ASSOCIATED 'RESERVOIR' LIGHT. STATUS PAGE DISPLAYED L HYD QUANTITY 0.43 RF. REFED QRH; NOTIFIED COMPANY AND REQUESTED FROM ATC RETURN TO ZZZ DUE TO POSSIBLE LOSS OF 'A' HYD SYS. SYS QUANTITY CONTINUED TO DECLINE TO 0.24. WHEN ABEAM ZZZ; EXTENDED GEAR NORMALLY. DURING FLAP EXTENSION; EICAS DISPLAYED 'L HYD ENG PUMP' AND ASSOCIATED 'LOW PRESSURE' LIGHT ILLUMINATED. REFED QRH; LOSS OF L HYD SYS; ADVISED ATC; FLT ATTENDANTS; AND PAX OF DIVERSION TO ZZZ1 DUE TO LONGER RWY LENGTHS AVAILABLE PER AGREEMENT WITH DISPATCHER. LANDED RWY 9R ZZZ1; TAXIED CLR OF RWY END; AND WAS TOWED TO THE GATE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE PRESSURE LINE LOCATION AND FUNCTION THAT FAILED IN THE L SYS IS UNKNOWN. THE RPTR SAID MAINT ONLY REVEALED A PRESSURE LINE FAILED. THE RPTR STATED NO EMER WAS DECLARED. CALLBACK CONVERSATION WITH RPTR ACN #598311 REVEALED THE FOLLOWING INFO: THE RPTR STATED THE LOSS OF THE L HYD SYS FLUID WAS CAUSED BY A FLEXIBLE HYD LINE ON THE L MAIN LNDG GEAR. THE RPTR SAID THE L MAIN LNDG GEAR WAS COMPLETELY WET FROM THE FLUID AND SUSPECTS THE LINE WAS A BRAKE PRESSURE LINE.