Story ID: 
NTSB Releases Prelim on B737-Challenger Near-collision
By: Matt Thurber
Caption: Report notes the both airplanes' cockpit voice recorders were overwritten
Word Count: 983
The NTSB has published a preliminary report on the February 25 near-collision runway incursion involving a Flexjet Bombardier Challenger 350 and a Southwest Airlines (SWA) Boeing 737-800 at Chicago Midway International Airport (KMDW). The Aviation Investigation Preliminary Report noted that the “cockpit voice recorders for both airplanes were overwritten,” although the “SWA flight data recorder (FDR) and data from the Flexjet FDR were sent to the NTSB’s Vehicle Recorder Laboratory in Washington, D.C. for analysis.”
The incursion resulted in the SWA 737 crew aborting the landing on Runway 31C and performing a go-around after Flexjet Flight 560 (LXJ560) crossed the active runway in front of the 737. The 737 passed less than 200 feet behind the Challenger, according to the NTSB.
Clear weather prevailed as the SWA 737 crew flew the ILS approach to Runway 31C, with the captain as pilot flying and first officer (FO) in the pilot monitoring role. After shutting off the autopilot at about 500 feet, both pilots saw the Challenger “taxiing on a surface perpendicular to their runway and assumed it would be holding short of Runway 31C.” At 100 feet, when he heard the avionics call out the altitude, the FO “realized that the [Challenger] was not stopping and was going to cross onto Runway 31C. The FO stated that he called for a go-around and the captain executed it. The flight crew indicated that standard go-around procedures were applied, and the maneuver was executed smoothly and without incident.”
Parked at the Signature ramp on the west side of the airport, the Challenger crew had requested a taxi clearance and were given instructions that they later said were confusing, to taxi to Runway 22L via Foxtrot and to hold short of Runway 4L. 
The airport diagram for KMDW shows that to get to Foxtrot, the Challenger would first need to taxi on Alpha, which is directly across from the Signature FBO. After requesting clarification, the ground controller cleared the Challenger to taxi on Alpha to Foxtrot then hold short of Runway 4L/22R.
As they were taxiing on Foxtrot, the ground controller instructed the Challenger crew to “turn left on Runway 4 Left, cross Runway 31 Left, and hold short of Runway 31 Center.” (LiveATC.net captured this and the language in the following paragraph; the NTSB has not yet released the transcript from ATC recordings.—Ed.) 
The Challenger crew responded: “Right, left on two, 4 Left, cross two two, er, one three, uh, Center, Flexjet 560.” The controller indicated that the readback was incorrect and repeated the instruction: “Flexjet 560, negative. Cross Runway 31 Left, hold short Runway 31 Center.” The Challenger crew responded: “Cross 31 Left, hold short 31 Center, Flexjet 560.”
In the preliminary report, the NTSB said that the Challenger crew reported in post-accident statements “that as they turned left onto Runway 4L/22R, the sun was impeding visibility from the right side of the aircraft, however, they did not recall seeing any hold-short line/pavement markings or any other signs for the 31L intersection as they taxied onto runway 04L/22R. They stated that taxiway F and runway 13R/31L were in close proximity to each other and by the time the nosewheel had straightened out, they were likely halfway across runway 13R/31L. They further stated that runway 13R/31L appeared to have a very similar width to taxiways and that they had not recognized it as a runway. The captain stated that as he approached runway 13C/31C he had thought it was runway 13R/31L. As they approached the runway intersection, the crew stated they both looked to the left and to the right and did not observe the SWA airplane on final. As LXJ560 approached the hold-short line for Runway 31C the ground controller instructed LXJ560 to hold short, but the transmission was not acknowledged.”
In the LiveATC.net recording of the ground control frequency around the time of the go-around, after the controller made other calls to various aircraft, a garbled transmission, likely being stepped on by another transmission, can be heard that sounds like someone is saying, “Flexjet 560 hold short, Flexjet 560” but it is not clear where that transmission came from.
The preliminary report acknowledges that the ground controller told the Challenger crew to hold short but it does not mention anything about the radio call being garbled. “As LXJ560 approached the hold-short line for Runway 31C the ground controller instructed LXJ560 to hold short, but the transmission was not acknowledged,” according to the NTSB.
A few seconds after telling the crew to hold short, the ground controller instructed the Challenger to hold its position but the captain continued taxiing across the active runway and then stopped after making sure the airplane’s tail wasn’t over the runway. The controller then asked the Challenger crew to taxi forward and hold short of Hotel then after they stopped, informed the crew that they might have a possible pilot deviation and to write down and call a phone number.
After taxiing to the north triangle area and making the phone call, the captain “contacted the operator [Flexjet] to notify them of the possible pilot deviation, assessed their well-being to continue the flight, and subsequently departed about 25 minutes after the runway incursion. The rest of their flight was uneventful.”
The NTSB’s operational factors group and a human performance specialist interviewed the Challenger crew on March 4 and the SWA crew on March 13. The FAA provided certified ADS-B data and audio recordings to the NTSB. Midway Airport supplied photos of the runway environment “showing the runway signs (vertical white-on-red signs erected on either side of the runway hold-short position markings) and the hold-short line for runway 13C/31C.” The hold-short line is painted on Runway 4L, the runway on which the Challenger was taxiing.