ASN Wikibase Occurrence # 309433
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Narrative:A Diamond DA40 NG, (HB-SGD) and a Socata TB21 (N705TB) were involved in a serious airprox incident near Bellinzona, Switzerland.
|Wednesday 3 March 2021
Diamond DA40 NG Diamond Star
|Year of manufacture:
|Fatalities: 0 / Occupants: 2
|6 km N of Bellinzona -
| En route
|Zürich-Kloten Airport (ZRH/LSZH)
|Lugano Airport (LUG/LSZA)
| Accident investigation report completed and information captured
The DA40 departed Zurich Airport (LSZH) at 10:43 on a flight bound for Lugano (LSZA).
According to the flight plan, the flight was under IFR and would change to VFR at predetermined Point Bellinzona.
At about 11:15, the Socata TB21 took off from Lugano-Agno Airport for a flight with destination Damme (EDWC). The flight consisted of an initial VFR portion to a predefined IFR navigation point.
After leaving the Lugano control zone, the pilot of N705TB reported to the Locarno area control center at 11:22 and informed the air traffic controller that he was climbing at Mezzo at 4600 ft and was flying north from Monte Ceneri to the UTAVO navigation point (IFR joining point). The pilot of the N705TB further stated that he would fly through to the south and therefore outside the CTR. The Locarno controller informed him to make the northbound transit at 4000 ft or higher and to report back when leaving the frequency. At 11:24, the Locarno area traffic controller instructed the pilot of N705TB to call Zurich Information. At 11:25, the pilot of N705TB contacted Zurich Information and reported the current position of Bellinzona at 8800 ft AMSL while climbing to 10 000 ft AMSL. As N705TB was on a direct path to the UTAVO navigation point, it was flying north along the left, western side of the Riviera valley at this time. After the initial call of N705TB to Zurich Information, the pilot was assigned a new transponder code twice in succession within a short period of time. The pilot of N705TB assumed that he would in any case receive traffic information about other aircraft concerning him.
At the same time, HB-SGD was also at 10 000 ft AMSL north of Bellinzona, flying south on the right, western side of the valley. The pilot of the HB-SGD stated that at 11:27, he had received a warning from the onboard Traffic Advoisory System (TAS) collision warning device about another aircraft that was slightly lower at the 1 o'clock position in front of the HB-SGD at a distance of 2 miles (NM). Both occupants of the HB-SGD increased their lookout for the other aircraft but did not see it. About 20 seconds later, the occupants of the HB-SGD spotted the other aircraft slightly to their right, crossing in front of them on a climb at the same altitude. The pilot of the HB-SGD informed the Locarno air traffic control center with the following words: "Very near approach over Arbedo, N registration". No reply was received from the Locarno air traffic control center.
According to Skyguide's radar evaluation, the serious incident occurred at 11:27:21 with a vertical distance of 100 ft (30 m) and a horizontal distance of 0.1 NM (185 m). The pilot of N705TB did not see HB-SGD at any time. Neither aircraft had received traffic advisories from the Locarno Area Traffic Control Center or from Zurich Information because the two air traffic controllers had no capacity to issue such advisories. The two aircraft were on different radio frequencies at the time of the serious incident. After the serious incident, the aircraft involved continued.
The serious incident in which two aircraft came dangerously close to each other can be attributed to the fact that, on the one hand, the crew of the N705TB aircraft did not recognize the oncoming HB-SGD aircraft and was not supported by technical aids and, on the other hand, because the crew of the HB-SGD was warned by an active TAS, but the latter recognized the oncoming aircraft too late despite intensified lookout.
In addition, the crew of the N705TB relied on traffic information from the flight information service. However, like the area traffic control center in Locarno, this was not in a position to warn of the other aircraft for capacity reasons. As a result, the crews of both aircraft were left to their own devices, as is usual in Class E airspace, according to the "see and avoid" principle.
The serious incident thus demonstrates once again the value of compatible collision warning systems for safe flight control.
| Final report
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