What was found
FLT NR 3517 - PIT - IMMEDIATELY AFTER ROTATION, GEAR WOULD NOT RETRACT AND RECEIVED "LG/AIR/GND FAIL" MESSAGE ON THE EICAS. MAINTENANCE REPLACED THE LEFT NOSE DOWNLOCK PROX SWITCH CANNON PLUG, SERVICED THE MLG STRUTS, INSPECTED ALL OF THE PROXIMITY SWITCHES IN THE SYSTEM, AND PERFORMED SEVERAL GEAR SWINGS. NO FURTHER DEFECTS NOTED.