What was found
FLIGHT FROM CDC TO GCN; AFTER TAKEOFF WHEN LANDING GEAR WAS SELECTED UP THE CREW RECEIVED AN AURAL WARNING WITH ASSOCIATED WARNING LIGHTS INDICATING THE LEFT (GREEN) HYDRAULIC FLUID QUANTITY LEVEL WAS LOW. THE LANDING GEAR WAS SELECTED DOWN WHICH EXTENDED AND LOCKED DOWN. THE AIRCRAFT RETURNED TO CDC AND LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED THE AIRCRAFT FOR SIGNS OF HYDRAULIC LEAKS BUT NONE WERE FOUND. THE GREEN SYSTEM WAS SERVICED WITH FLUID AND THE AIRCRAFT WAS RETURNED TO SERVICE. THE CAPTAIN REPORTED AFTER LANDING AT CDC THAT THERE WERE NO FURTHER ISSUES WITH THE SYSTEM.