What happened
On August 9, 2011, a serious air traffic conflict occurred in Class E airspace approximately three nautical miles northwest of the WLD radio beacon. The incident involved a Cessna 172RG operating under IFR for training purposes and a Mooney M 20R flying under VFR.
At approximately 12:01, the air traffic control system generated a "predicted" Short-Term Conflict Alert (STCA), turning the radar targets yellow. By 12:02, the alert escalated to a "current" status, changing the targets to red. Despite these automated warnings, the aircraft continued on their respective paths. At 12:04, the two aircraft passed within a distance of just 0.09 NM at nearly the same altitude. The crew of the Cessna reported that the Mooney appeared suddenly on their right, making an evasive maneuver impossible, while the student pilot was focused on instruments using training goggles.
In the Mooney, the pilot observed the Cessna from a distance of about two nautical miles and noted it on the onboard traffic warning system. However, the pilot elected to maintain the existing course and altitude, believing the situation was not critical.
The investigation
The BFU investigation focused on the actions of the flight crews and the air traffic controller. The investigation examined radar recordings, which confirmed the extreme proximity of the two aircraft. Investigators also reviewed the operational environment at the control center, noting that a lengthy, ten-minute shift handover was occurring simultaneously with the event.
Technical analysis of the radar display revealed that overlapping data labels made it difficult to track specific flight information. The investigation also looked into the effectiveness of the STCA system's acoustic and visual alerts, finding that the controller's attention was not successfully drawn to the conflict by the existing warning protocols.