A King Air has four steps on the cabin door to allow crew and passengers accessible entry to the aircraft. Lighting on the steps is optional. If the steps are equipped with lighting, the bulbs are located on the bottom side of each step assembly and controlled by a threshold light. The lights can only be in use when the airstair door is open. Part number MCOC28926-1 is a lighted, middle step found on King Air 90, 100, 200, 300, and 350 aircraft models. Replacement of the middle and top steps will be required after prolonged exposure to heavy loads and stress. The plastic light covers may crack and steps can break away from or bend the metal framing.