Narrative:

Our aircraft had just finished a 'heavy' maintenance check before our flight. During that heavy check; the landing gear was replaced. All indications on preflight and the maintenance sign offs were normal. Passing approximately 10;000; a low hydraulic fluid EICAS message appeared; followed shortly by a hydraulic system pressure message. We followed the checklists; securing the #4 hydraulic system. At maintenance's request we returned to our departure airport; dumping approximately 100;000 pounds of fuel to arrive below maximum landing weight. When we lowered the gear (by alternate means); the left wing landing gear did not show 'down and locked.' we complied with all appropriate checklists; but did not get a down and locked indication. We did a low pass at 300 feet and approximately 200 knots to have tower personnel visually check the gear. It appeared normal. We [advised ATC] at this time and asked for equipment to be standing by. We landed without event. We cleared at the high speed; shut down engines; and maintenance towed the aircraft to a gate. Post flight inspection revealed a 3 inch hole in gear actuator. The gear was down but not locked.

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Original NASA ASRS Text

Title: B747-400 Captain reported a loss of hydraulic fluid during climb. A decision was made to return to the departure airport; which necessitated dumping fuel; and using an alternate method for extending the landing gear. A successful landing followed.

Narrative: Our aircraft had just finished a 'heavy' maintenance check before our flight. During that heavy check; the landing gear was replaced. All indications on preflight and the maintenance sign offs were normal. Passing approximately 10;000; a Low Hydraulic Fluid EICAS message appeared; followed shortly by a Hydraulic System Pressure message. We followed the checklists; securing the #4 hydraulic system. At maintenance's request we returned to our departure airport; dumping approximately 100;000 pounds of fuel to arrive below maximum landing weight. When we lowered the gear (by alternate means); the left wing landing gear did not show 'down and locked.' We complied with all appropriate checklists; but did not get a down and locked indication. We did a low pass at 300 feet and approximately 200 knots to have Tower personnel visually check the gear. It appeared normal. We [advised ATC] at this time and asked for equipment to be standing by. We landed without event. We cleared at the high speed; shut down engines; and maintenance towed the aircraft to a gate. Post flight inspection revealed a 3 inch hole in gear actuator. The gear was down but not locked.

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.