What was found
AFTER ROTATION PILOT SELECTED LG HANDLE IN THE RETRACT POSITION. LG REMAINED EXTENDED & LOCKED WITH THREE GREEN INDICATOR LIGHTS ILLUMINATED. PILOT SWITCHED THE GEAR CONTROL & INDICATOR TO RT BUS & VERIFIED THE EMER GEAR RELEASE SYS WAS PROPERLY STOWED, GEAR DID NOT RETRACT. PILOT DECIDED TO RETURN & LANDED WITHOUT FURTHER INCIDENT. TROUBLESHOOTING REVEALED AIR TRAPPED IN LG STRUT PREVENTED PISTON IN STRUT FROM FULLY EXTENDING. BLEED STRUT & ENSURED PISTON WAS FULLY BOTTOMED OUT. SERVICED STRUT IAW MM & CYCLED LG SEVERAL TIMES TO ENSURE PROPER OPERATION. ALL CHECKS WERE NORMAL.