ASN Wikibase Occurrence # 308834
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| Date: | Thursday 18 March 2021 |
| Time: | 16:43 |
| Type: |  Robinson R44 II |
| Owner/operator: | Mountainflyers |
| Registration: | HB-ZWJ |
| MSN: | 14433 |
| Year of manufacture: | 2021 |
| Fatalities: | Fatalities: 0 / Occupants: 4 |
| Aircraft damage: | None |
| Location: | 3 km W of Thun -
 Switzerland
|
| Phase: | En route |
| Nature: | Training |
| Departure airport: | Berne-Belp Airport (BRN/LSZB) |
| Berne-Belp Airport (BRN/LSZB) | |
| Confidence Rating: |  Information verified through data from accident investigation authorities |
On the afternoon of March 18, 2021, two single-seater Northrop F-5E fighter jets of the Swiss Air Force, registered as J-3044 (call sign 'Duck 51') and J-3094 (call sign 'Duck 52') took off from Payerne Air Base for an air combat exercise.
At around the same time at 15:50 hrs a flight instructor took off from Bern Belp Airport with a student pilot and two other passengers in a Robinson R44 II helicopter, registered as HB-ZWJ, for a training flight. The route was planned via Thun and Spiez through the Engstligental and on via Lenk and Zweisimmen through the Simmental via Thun back to Bern. At 16:39 hrs the helicopter was at the exit of the Simmental at about 5100 ft AMSL and started a slight descent.
At the end of the exercise, shortly before 16:40, the two F-5E's made the return flight from the work area over the Bernese Oberland to Payerne. The pilots of the F-5E's remained in constant radio contact with the tactical command center "Batman" of the Air Force Operations Center for the purpose of further traffic information regarding other aircraft. The F-5E pilots were looking for an adequate hole in the cloud cover to descend to lower altitudes.
Before the formation of two descended below the cloud cover, they reported this to the control center, which confirmed that they did not see any other aircraft on the radar.
In the Diemtig Valley region, the F-5E fighter jets descended below cloud cover at 16:41 and their flight path led back to Payerne via Thun and Freiburg over Lake Thun. The cloud base in the Thun region was about 6200 ft AMSL that afternoon. Good weather conditions prevailed under the cloud cover, which allowed a return flight based on visibility.
At 16:42:30 hrs "Batman" reported to the crews of the F-5E, which at that time were just outside Thun, that he had lost radar contact with the F-5E. The F-5E pilots from that point on were in responsible for spotting and avoiding other aircraft.
At 16:43, approximately 3 km west of Thun, the formation of two crossed the flight path of HB-ZWJ at an altitude of approximately 4800 ft above sea level, which was flying at a ground speed (GS) of 115 kt. The ground speed of the two F-5E's was around 470 kt in this phase. The pilot of HB-ZWJ only recognized the two combat aircraft immediately before the crossing and estimated the altitude above the helicopter's flight altitude to be around 30 to 50 m.
Conclusion:
The serious incident, in which two combat aircraft and a helicopter approached dangerously, can be attributed to the fact that the combat aircraft crews did not visually recognize the helicopter and were not supported by technical aids. In addition, they were unable to receive any traffic information relating to the helicopter, since the two combat aircraft and the helicopter were moving outside of radar coverage at the time of the dangerous convergence.
Sources:
https://www.sust.admin.ch/inhalte/AV-berichte/HB-ZWJ_2xF-5sumB_D.pdf
Revision history:
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