Incident Overview
On September 16, 2010, at approximately 6:49 a.m. CDT, a near-midair collision occurred between US Airways Flight 1848 (AWE1848), an Airbus A320 operating as a scheduled passenger flight to Philadelphia, Pennsylvania, and Bemidji Aviation Services Flight 46 (BMJ46), a Beech 99 cargo flight en route to LaCrosse, Wisconsin. AWE1848 carried five crewmembers and 90 passengers; BMJ46 carried only the pilot. Weather conditions at the time included a ceiling of 900 feet and visibility of 10 miles.
Sequence of Events
At 0647:50, the local north controller (LCN) cleared AWE1848 into position and hold on runway 30R. At 0648:02, the LCN controller instructed the pilot to fly runway heading and cleared the flight for takeoff. At 0649:26, the LCN controller instructed AWE1848 to turn left heading 260 and contact departure control. The pilot acknowledged.
Meanwhile, at 0648:15, the local south controller (LCS) contacted the Minneapolis departure radar controller to obtain approval for BMJ46 to fly heading 180 after takeoff. Approval was granted, and at 0648:31, the LCS controller instructed BMJ46 to turn left heading 180 after departure and cleared the pilot for takeoff on runway 30L. The pilot acknowledged. BMJ46 departed and continued straight out from runway 30L for about two miles.
At 0650:26, the LCS controller asked BMJ46 if it was in the turn. The pilot replied with a request for clarification, and the controller reiterated the heading 180 instruction. At 0650:54, the LCS controller instructed BMJ46 to maintain 4,000 feet and heading 180. The pilot acknowledged and reported having traffic. At 0651:41, BMJ46 transmitted that it was going to departure, and the controller approved the frequency change.
At 0649:49, AWE1848 made a partial transmission to departure control. At 0649:55, the pilot of AWE1848 reported seeing an aircraft off the left side and hearing it pass by. The departure controller responded that the other aircraft appeared to be straight out. The pilot mentioned a TCAS resolution advisory (RA) and that they heard the aircraft go by. The departure controller stated that the 99 (BMJ46) was off the right and straight out.
Review of recorded radar data showed that the paths of the two aircraft crossed at 0649:58. A second error occurred later when the LCS controller instructed BMJ46 to turn left to heading 180 while the aircraft was about two miles northwest of the airport, again creating a conflict with separation of 500 feet and 1.23 miles, below the required minimum of 1,000 feet or 3 miles.
Controller Actions
At the time of the incident, two local controllers were on duty. The LCN controller was responsible for runway 30R, and the LCS controller was responsible for runway 30L and runway 17/35 (the latter inactive). Initially, the LCS controller was combining the LCN, LCS, and LCW positions. About 0645, the LCN position was split off, and the new LCN controller took over.
The LCS controller stated that he coordinated a southbound heading for BMJ46 with the departure radar controller. He became distracted by handling Air Transport 808, a DC-8 that had landed on runway 30L, and did not notice that BMJ46 was not turning as expected. He assumed BMJ46 would turn before reaching the end of runway 30L. The LCN controller stated that he heard the clearance for BMJ46 but did not expect it to be a conflict because it was assigned a heading of 180. He scanned for traffic and did not see BMJ46, assuming it had turned. Both controllers acknowledged that they had assumed BMJ46 would turn sooner than it did.
Aftermath
US Airways filed a TCAS report on September 17, 2010. The report described the TCAS RA that commanded a climb to avoid the conflicting traffic, and the pilots heard the other aircraft pass below. The tower supervisor had both controllers relieved from their positions to participate in an investigation. The administrative supervisor reviewed audio recordings and radar data. Both controllers participated in a roundtable discussion later that day. The LCS controller filed an Air Traffic Safety Action Program (ATSAP) report.