What happened
On April 21, 2016, a serious near-collision occurred approximately 10 NM northeast of Friedrichshlarfen Airport (EDNY), Germany. The incident involved a Fokker 50, registration OO-VLF, operated by Vlaamse Luchttransportmaatschappij N.V. (VLM), and a Piper PA-28RT-201T, registration OK-ELL.
The aircraft were operating under different sets of rules and communicating with different air traffic control units. The Fokker 50 was conducting an instrument flight rules (IFR) approach to runway 24, while the Piper was operating under visual flight rules (VFR) from the southeast. During the encounter, the horizontal separation between the two aircraft dropped to just 0.5 NM, with a vertical separation of only 100 ft.
The investigation
The Swiss Transportation Safety Investigation Board (SUST) examined the operational procedures in place during the "AERO Friedrichshafen" aviation fair. The investigation focused on the coordination between Skyguide (managing the ARFA sector) and Austro Control GmbH (managing the Friedrichshafen tower).
Investigators analyzed the specific VFR approach charts published for the event, which recommended a flight corridor for VFR traffic not exceeding 4000 ft AMSL. This specific instruction meant that VFR aircraft approaching from the southeast had to cross the runway axis. The investigation also reviewed the technical performance of the Fokker 50's Traffic Collision Avoidance System (TCAS) and the communication logs between the various air traffic controllers and the flight crews.
Findings
Several contributing factors led to the dangerous encounter:
- The operational concept for managing simultaneous IFR and VFR traffic during the airshow contained systemic risks.
- The flight crews were not communicating with the same air traffic control unit, as the airliner was under radar guidance while the light aircraft was in contact with the tower.
- Coordination between the different air traffic controllers was insufficient.
- The traffic information provided by the tower to the pilot of the light aircraft was delayed.
- The TCAS on the Fokker 50 did not issue a resolution advisory because the aircraft's lateral maneuver did not trigger the system's alert criteria.
- Both crews achieved visual contact with the other aircraft only at a very late stage.
- Environmental factors, including a low sun position, hindered visibility from the cockpit of the airliner.
Safety action
SUST issued safety recommendation No. 541, calling on the Federal Aviation Office (BAF) to collaborate with DFS, Skyguide, and Austro Control GmbH to review and improve the operational concept used during aviation trade fairs to mitigate risks associated with mixed IFR and VFR traffic.