What happened
On November 19, 2019, a private flight involving a Schweizer HU269 helicopter, registration HB-ZLB, was performing a local flight at Lausanne-La Blécherette (LSGL). After completing a local circuit, the pilot decided to join the final approach for runway 36 via the southern sector. To avoid turbulence caused by the Bise wind, the pilot opted for a higher approach altitude than usual, establishing on long final at 3,100 ft.
Simultaneously, a Beechcraft King Air (registration D-ICTR) was arriving from Germany. The crew, consisting of a captain and a safety pilot, had transitioned from instrument flight rules to visual flight rules (VFR) near Saint-Prex. Upon entering the southern sector of the airfield, the crew announced their position at 3,300 ft.
As the aircraft approached the final approach path, the crew of the D-ICTR observed the helicopter at a higher altitude. Given the significantly higher approach speed of the twin-engine aircraft and what they perceived as sufficient vertical separation, the captain decided to execute an overtaking maneuver by passing underneath and to the right of the helicopter. The crew announced their intention to pass the preceding traffic on the right and below.
As the helicopter descended through 2,900 ft, the pilot heard a fragmented radio transmission in English regarding traffic passing below. Shortly thereafter, the aircraft appeared directly beneath the helicopter. The pilot of the HB-ZLB immediately applied maximum deceleration to attempt to regain separation while continuing the approach.
The investigation
The investigation, conducted by the Swiss Transportation Safety Investigation Board (SUST), utilized pilot statements and radar data from Skyguide to reconstruct the flight paths. The inquiry examined the communication procedures at Lausanne-La Blaterette, where pilots use an Aerodrome Flight Information Service (AFIS) and are permitted to communicate in both French and English.
Findings
- The investigation identified that the overtaking maneuver from below created a high risk of collision, particularly because such a tactic leaves little margin for error should the preceding aircraft experience an unexpected event, such as an engine failure.
- The use of different languages (French and English) for radiotelephony between the two crews contributed to the incident.
- A significant difference in the approach characteristics between the helicopter and the fixed-wing aircraft played a role in the close encounter.
- The minimum separation reached during the airprox was 70 meters horizontally and 400 feet vertically.