What happened
On May 17, 2018, a Tecnam P2002-JF, registration HB-KOU, was conducting a training flight near Biel, Switzerland. While cruising at approximately 3,000 ft AMSL at a speed of 95 knots, the student pilot was monitoring ATIS information for Biel-Kappelen (LSZP). During the flight, the crew was surprised by an oncoming aircraft flying at a slightly lower altitude. To avoid a collision, the student pilot initiated a left turn. The two aircraft crossed paths with a lateral separation of between 100 and 200 meters. The occupants noted that the PowerFlarm collision warning system provided an alert only very late, either just before or during the actual crossing.
The investigation
The investigation focused on the performance of the collision warning technology used during the encounter. Analysis of the PowerFlarm (Core ADS-B type) installed in HB-KOU revealed that its transmission range was significantly lower than the average for similar systems recorded over the preceding 28 days. Furthermore, the investigation found that the signal radiation around the aircraft was spatially very limited, making it difficult for other aircraft equipped with Flarm technology to detect HB-KOU early.
Findings
- The insufficient transmission power and receiver sensitivity of the onboard PowerFlarm were the primary reasons the warning was delayed.
- The lateral separation between the two aircraft was only 100 to 200 meters.
- The investigation highlighted a recurring safety deficit regarding the unverified functional range of Flarm-based collision warning systems, a known issue previously identified in other Swiss aviation incidents.
- There is a lack of widespread awareness regarding tools available to check the signal strength and antenna characteristics of these devices.