Abstract: At approximately 10:00 p.m., on January 4, 2013, four employees were working for American Building Maintenance performing custodial assignments of cleaning and maintaining the interiors of nine airplanes owned by Southwest Airlines. While the employees were cleaning the plane, Employee #1 wanted to check the life vests beneath the seats of the plane. The employee realized that they were running late and shouted out, I am moving the stairs. Another employee stated, he heard the instruction. These are the mobile stairs placed at the plane's doorway in order to gain access to the plane. The stairs are pulled by a tug vehicle. As another employee drove out the tug and pulled the mobile stairs, another employee, who was standing next to the Employee #1 that heard the instruction, walked to the entrance and stepped out the plane doorway and fell approximately 9 ft landing on the concrete ground. Employee #1 was taken to an area hospital, where he was treated for a leg fracture and released.