What was found
LP NR 281139-1; AIR RETURN; AT 12,000 FT HYDRAULIC PUMP PRESS REDUCTION GEAR DOOR OPEN LIGHT AND LT MAIN GEAR DOOR UNSAFE LIGHT CAME ON, COMPLIED WITH QRH. CYCLED GEAR LT MAIN GEAR UNSAFE LIGHT REMAINED ON. INSEPECTED LT MAIN GEAR UPLOCK, FOUND PROX SWITCH SENSOR WITH NO AIR GAP, ADJUSTED AIR GAP TO WITHIN LIMITS. OPS CHECK GOOD.