What happened
On April 28, 2011, a Piper PA-28, registration SE-ILE, was conducting a navigation training flight from F17 Ronneby Airport. The aircraft, carrying an instructor and a student pilot, was cleared to depart via the Tving waypoint at an altitude of 1,500 feet QNH or lower.
Simultaneously, a two-ship formation of JAS 39 Gripen military jets, operating under the call sign GATOR 61 MIKE, was performing a high-speed visual approach to runway 01 via the same Tving waypoint. The military formation was descending toward a traffic circuit altitude of approximately 40 and 500 meters QFE.
As the aircraft converged, the pilot in the rear of the Gripen formation spotted the Piper PA-28 only moments before the encounter. Despite a quick "heads-up, traffic" warning to the flight lead, the military jets passed directly over the light aircraft at a distance estimated between 50 and 60 meters. The closing speed between the two aircraft was approximately 140 meters per second.
The investigation
The Swedish Accident Investigation Authority (SHK) examined radio communications, radar data, and interviews with the pilots and air traffic controllers. The investigation focused on why the conflict was not detected by air traffic control (ATC) or the pilots before the near-miss occurred.
Investigators found that the transponder on SE-ILE had not been activated prior to takeoff, meaning the aircraft did not appear on the secondary radar. Furthermore, the investigation scrutinized the coordination between the tower controller (AD1) and the terminal controller (T17). It was noted that the tower controller had cleared the Piper PA-28 to a higher altitude than usual to avoid turbulence, which placed it at nearly the same altitude as the incoming military jets.
Findings
- The primary cause of the incident was the failure to notice the impending conflict between the departing civil aircraft and the incoming military jets due to insufficient follow-up on issued clearances.
- The use of the Tving waypoint as both an exit point for civil VFR traffic and an entry point for military jet traffic created a significant risk factor.
- The transponder in SE-ILE was not turned on, preventing air traffic controllers from having a complete radar picture of the traffic situation.
- Deficiencies in coordination between air traffic controllers were identified, including a lack of verbal read-back during coordination and incorrect notation of flight paths on the flight progress strips.
- The high approach speed assigned to the JAS 39 Gripen formation reduced the time available for the pilots to detect the smaller aircraft and perform evasive maneuvers.