Confusion over similar-sounding flight numbers is under investigation as the cause of a close call between two airliners taking off on intersecting runways at Midway Airport, an aviation source said Wednesday. 
 
 A Southwest Airlines plane, Flight 3828, was cleared for takeoff on runway 31 Center on Tuesday night, according to the Federal Aviation Administration. As Flight 3828 began its takeoff roll, Delta Air Lines Flight 1328 also began rolling on runway 4 Right without clearance from the Midway tower, according to the preliminary FAA investigation. 
 
 Both planes were operating at full takeoff power, which is standard procedure on the Southwest Side airport's relatively short runways, the source said. 
 
 The controller directing both planes spotted the Delta plane's movement and ordered the Delta pilots to stop immediately, the FAA said. The Southwest pilots also hit the brakes. Each aircraft traveled about one-third down its respective runway, stopping 2,000 to 3,000 feet short of the runway intersection between 31 Center and 4 Right, the source said. 
 
 Before the incident, a Midway ground controller had notified both pilots about the similar and potentially confusing flight numbers of the two planes waiting to depart, and he advised the pilots to listen carefully to radio calls, according to tapes of the incident, which are on http://www.LiveATC.net 
 
 On the transmission, the tower controller is heard clearing Southwest Flight 3828 for takeoff. But when the Southwest pilot radios back confirmation, his voice is obscured, or "stepped on," by a dual transmission, apparently from Delta Flight 1328. During a dual transmission, each pilot hears only some of what is being communicated. 
 
 Zbigniew Bzdak, Chicago Tribune Passengers wait to travel at Midway Airport in July 2012. A Southwest Airlines plane, cleared for takeoff on Midway runway 31 Center on June 16, 2015, came close to colliding with a Delta Air Lines flight that had not been cleared for takeoff. Passengers wait to travel at Midway Airport in July 2012. A Southwest Airlines plane, cleared for takeoff on Midway runway 31 Center on June 16, 2015, came close to colliding with a Delta Air Lines flight that had not been cleared for takeoff. (Zbigniew Bzdak, Chicago Tribune) (Zbigniew Bzdak, Chicago Tribune) 
 
 A second dual transmission then occurs, and seconds later, as the Southwest plane is accelerating down runway 31 Center, the Delta plane is also on a takeoff roll on intersecting runway 4 Right, sources said. 
 
 A controller abruptly yells, "Stop, stop, stop, stop!" A pilot says, "Aborting," and another pilot announces, "SWA stopping." 
 
 After both planes safely make an emergency stop short of the intersection, the Southwest pilot is heard on the tape asking the control tower whether he mishandled his takeoff clearance. "Were we the ones cleared for takeoff?" 
 
 The controller responds, "Yes, sir, you were. You were doing what you were supposed to be doing." 
 
 "Delta took our —. Delta was rolling also?" the pilot asks. 
 
 "He took your call signs," the controller says. "Somebody kept stepping on you. I couldn't figure out who it was, that's why I reiterated that it was you that I was calling for takeoff." 
 
 The controller is also heard providing an FAA phone number and advising the Delta captain to report a pilot deviation. 
 
 The Southwest plane taxied back to the terminal for a safety check because of overheated brakes from the emergency stop, the source said. The plane ended up leaving for Tulsa, Okla. where it landed safely, according to a Southwest spokesman. 
 
 The Delta crew also contacted its company, but the plane quickly got back into the departure line and flew out of Midway to Atlanta, officials said. 
 
 Delta released a statement saying that it was "fully cooperating with the FAA's investigation." 
 
 The Delta plane, a Boeing 717-200, is designed to carry 110 passengers. It was not immediately known how many passengers were on the plane. The Southwest plane was a Boeing 737, and had 139 passengers and five crew members on board, according to Southwest officials. 
 
 The National Transportation Safety Board, which has investigated runway incursions at O'Hare International Airport in recent years, is expected to assign investigators to examine the incident at Midway, officials said. 
 
 Runway incursions involving planes taxiing on the airfield, taking off or landing are a top safety concern — much more so than the risk of a midair collision — and the FAA has worked with airports and airlines to reduce the danger at airports, officials said. 
 
 The FAA, as part of its NextGen air traffic modernization program, is developing a program to provide data communications between pilots and air traffic controllers in place of voice communications for many routine functions. 
 
 Data communications will improve safety by reducing communications errors that can occur during verbal exchanges, the FAA said, particularly involving pilots for whom English is a second language, as well as cut the time spent exchanging information and reconfirming it. 
 
 The new data system, which is likely years off, would also reduce delays, fuel burn and pollution, according to the agency. 
 
 Chicago Tribune's Carlos Sadovi contributed. 
 
 jhilkevitch@tribpub.com 
 
 Twitter @jhilkevitch 

 (CNN) Two commercial planes almost collided at Chicago Midway International Airport Tuesday night, the Federal Aviation Administration confirmed. 
 
 Southwest flight 3828 was cleared for takeoff and started on the runway, but simultaneously Delta Air Lines 1328 also began on an intersecting runway without proper clearance according to a statement released by the FAA. 
 
 It caused a potentially harrowing situation as two planes should never be rolling for takeoff on intersecting runways. 
 
 The on-duty air traffic controller noticed the two planes headed toward the intersection, immediately warning the Delta flight. The controller can be heard yelling, "stop, stop, stop!" in the audio recording of the incident, which occurred at about 7:40 p.m. on Tuesday. 
 
 Both flights stopped 2,000 feet from the runway intersection, later the Southwest flight went on to Tulsa with no additional problems. 
 
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– Two commercial planes flirted with disaster tonight after beginning their takeoffs on intersecting runways at Chicago Midway International Airport, the Chicago Tribune reports. "Stop, stop, stop, stop!" an air controller can be heard shouting on a recording of the incident posted at LiveATC.net. The two pilots—one on Southwest flight 3828, the other on Delta Air Lines 1328—were each going at full takeoff power when they hit the brakes 2,000 to 3,000 feet short of the runway intersection. It happened at about 7:40pm, CNN reports. "Were we the ones cleared for takeoff?" asks the Southwest pilot. Air controller: "Yes, sir, you were. You were doing what you were supposed to be doing." Southwest Pilot: "Delta took our —. Delta was rolling also?" Controller: "He took your call signs. Somebody kept stepping on you." From the transmission, it sounds like the planes' similar numbers created confusion. The controller had even warned the pilots about this ahead of time, but when the Southwest pilot radioed back to confirm his takeoff, his voice was "stepped on" or obscured by a second transmission that may have come from the Delta flight. The controller can later be heard telling the Delta captain to report his mistake. "Just knowing that there were two aircraft of that size headed to the same intersection at the same time … this could have been catastrophic," a commercial pilot tells CBS Chicago. The National Transportation Safety Board will likely investigate.