On September 11, 2019, about 1143 CDT, SkyWest flight 3019, a CRJ700, N710SK, collided with SkyWest flight 3039, a CRJ700, N765SK, during pushback at Chicago O'Hare International Airport (ORD), Chicago, Illinois. There were no injuries to the passengers and crew onboard either airplane. Both airplanes sustained substantial damage. Both flights were operating as 14 Code of Federal Regulations Part 121 scheduled passenger flights. Flight 3019 was scheduled from ORD to Detroit Metropolitan Airport (DTW), Detroit, Michigan, and flight 3039 was scheduled from ORD to Harrisburg International Airport (MDT), Middletown, Pennsylvania. SkyWest 3019 was cleared to push back from gate G19A, with the assistance of a tug driver and two wing walkers. The tug driver indicated he performed a walk around prior to the push back and did not notice any airplane behind flight 3019. The wing walkers were positioned with one walker on each side of the airplane. Both wing walkers stated they were aware another airplane was behind SkyWest 3019, but initially believed that the stopped airplane would clear the area before the accident airplane was fully pushed back. The tug driver started to push flight 3019 without getting the “all clear” signal from both wing walkers. The tug driver also stated he could not see the captain’s side wing walker during a portion of the push and was focused on where the landing gear was proceeding, rather than viewing the surrounding area and his wing walkers. The captain's side wing walker said he tried to get the driver's attention, telling him to stop (the tug driver had a headset on to communicate with the flight crew), and had to eventually approach the tug driver to get his attention. The FO's side wing walker said she gave the emergency stop "X" sign to the tug driver, but it appeared that tug driver didn't see it. The driver was unaware of any problems until the captain's side wing walker approached him and told him to stop. SkyWest 3039 had pushed back from gate H1A and transitioned to the H alleyway and waiting for clearance to taxi onto the West Line (behind flight 3019). While stopped, the captain stated that the airplane shook, but that he thought it was only jet blast from another airplane. He then received clearance to take the West Line, but as he taxied out of the alleyway, he was notified of the collision. Post-accident examination revealed the left horizontal and vertical stabilizers of SkyWest 3019 and the tail cone and left elevator of SkyWest 3039 were substantially damaged.