Narrative:

Aircraft was coming out of heavy maintenance with full gear replacement. After departure; at around 10;000 ft we got an EICAS message for low hydraulic system 4 fluid which was followed by low hydraulic system 4 pressure. All QRH checklist and procedures were completed. We contacted company via sat phone and were requested to return to departure airport; on return we dumped approximately 100;000 lbs of fuel. Checklist advised of prolonged time for flap and gear extension so we did it as early as possible; when gear was lowered by the alternate system; we got a main left wing gear not down and locked indication at this time [we advised ATC]. A fly by was requested from the tower and approved. About 300 ft and 200 knots for tower to verify gear position. Tower advised gear position seemed normal. Approach and landing completed; after clearing the runway we were towed to the gate. Once parked we observed that the left wing main gear had extended but not locked and that there was a 2 to 3 inch hole in the hydraulic actuator for the before mentioned gear.

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Original NASA ASRS Text

Title: B747 Captain reported a landing gear issue after receiving a Low Hydraulic System 4 Pressure warning.

Narrative: Aircraft was coming out of heavy maintenance with full gear replacement. After Departure; at around 10;000 ft we got an EICAS message for Low Hydraulic System 4 fluid which was followed by Low Hydraulic System 4 Pressure. All QRH checklist and procedures were completed. We contacted company via SAT Phone and were requested to return to departure airport; on return we dumped approximately 100;000 lbs of fuel. Checklist advised of prolonged time for flap and gear extension so we did it as early as possible; when gear was lowered by the alternate system; we got a main left wing gear not down and locked indication at this time [we advised ATC]. A fly by was requested from the tower and approved. About 300 ft and 200 knots for tower to verify gear position. Tower advised gear position seemed normal. Approach and Landing completed; after clearing the runway we were towed to the gate. Once parked we observed that the Left Wing Main Gear had extended but not locked and that there was a 2 to 3 inch hole in the Hydraulic actuator for the before mentioned gear.

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.