What happened
On July 13, 2013, a high-risk near-collision occurred approximately 1.8 NM east of Langenthal airfield. The incident involved a Cessna C525, registered HB-VPF, operating under instrument flight rules (IFR), and a glider, an ASK 21 with registration HB-1589, which was being towed by a Robin DR 400/180 R, registered HB-EUV, operating under visual flight rules (VFR).
The business jet departed Grenchen following a standard instrument departure route. Meanwhile, the glider and its tow aircraft had departed Zweisimmen earlier that morning. As the aircraft approached the Langenthal region, the glider pilot prepared to release from the tow rope. At this time, the pilot of the Cessna C525 noticed a yellow traffic alert on the TCAS display, though no audible warning was triggered. The pilot subsequently identified the glider combination and performed an evasive maneuver by disabling the autopilot and descending beneath the glider. The glider pilot later observed the business jet passing beneath the left wing before the aircraft climbed away.
At the moment of closest approach, the horizontal separation between the transponder-equipped aircraft was only 0.2 NM, with a vertical separation of just 25 ft.
The investigation
SUST examined the flight paths, radar recordings, and cockpit systems. The investigation confirmed that the weather conditions did not contribute to the event. Investigators also reviewed the communication between the aircraft and the Bern departure control center, noting that the two aircraft were in contact with different air traffic control units, which prevented them from hearing each other on the radio.
Findings
- The primary cause of the near-miss was the inadequate visual monitoring of the airspace by the crew of the Cessna C525.
- A systemic contributing factor was the lack of clear information on the instrument departure charts; the charts used for the departure from Grenchen failed to indicate that the procedure led the aircraft into Class E airspace.
- The separation between the aircraft was extremely minimal, reaching a vertical distance of only 25 ft.
- The crew of the tow aircraft did not observe the business jet at any point during the encounter.