On 13 October 2019, an Airbus A320neo (G-TTND) being operated by British Airways on a scheduled international passenger flight from London Heathrow to Zurich as BA716 (callsign BAW14R) and a Rockwell Commander 112 (HB-NCB) being privately operated under VFR on an international passenger flight from Locarno to Donaueschingen-Villingen by Gamma Air were involved in a near mid air collision at 6000 feet QNH approximately 18 nm north west of Zurich in day VMC. Minimum separation was 1.2 nm laterally and 425 feet vertically. Both aircraft subsequently completed their flights without further event.
This Serious Incident occurred on 13 October 2019 and was reported to the Swiss Transportation Safety Investigation Board (STSB) the following day. However, an Investigation was not opened until 19 November 2019. Recorded ATC data was used as a basis for the Investigation.
The A320 Captain was born in 1970 and had a total of 11,000 hours flying experience of which 7,850 hours were on type and the A320 First Officer, born in 1989, had a total of 1,011 hours flying experience of which 282 hours were on type. The pilot of the light aircraft was a Swiss citizen and PPL holder born in 1966 who had 686 hours flying experience of which 158 hours was on type.
The conflict occurred in German airspace which formed part of the Class ‘C’ airspace of sector 6 of the Zurich TMA which had a base of 5,500 feet QNH below which the airspace was uncontrolled (Class ‘G’). This meant that whilst IFR traffic at 6000 feet QNH must be separated from other IFR traffic by 1000 feet, separation from uncontrolled VFR traffic below at 5,500 feet QNH was only 500 feet.
It was noted that a few minutes after checking on the Zurich APP Control West frequency, the A320, which was being vectored towards final approach at its destination, had been cleared to descend to FL060. However, within a few seconds of issuing that clearance, the controller observed a VFR Display Priority (VDP) alerting to a light aircraft below climbing into the TMA without clearance. An STCA activation was then triggered and four seconds later, the controller instructed the A320 crew to turn right onto a radar heading of 120° and provided information in respect of the conflicting traffic.
Twenty four seconds later, the two aircraft crossed each other with a 425 feet vertical separation when 1.2nm apart laterally. The A320 crew did not see the light aircraft and they did not receive a TCAS RA. The controller subsequently commented that their workload at the time of the conflict had been low which had favoured its early detection.
The light aircraft pilot was working Zurich Information and had undertaken not to climb higher than 5500 feet QNH until reaching the northern limit of the TMA which indicated that he was aware of the lower limit of the TMA. He was also navigating using electronic navigation software and a backup aeronautical chart and should thus have been able to conduct a VFR flight without airspace infringement. Both flights subsequently continued their flights to their respective destinations without further event.
The annotated ground tracks of the two aircraft based on radar recordings. [Reproduced from the Official Report]
Why It Happened
The Investigation was not able to determine why the airspace incursion had occurred other than because of the light aircraft pilot’s inattention to the airspace category boundary and/or his lack of awareness of the location of his aircraft in relation to the northern lateral extent of the TMA. However, it was noted that reported airspace infringements of the Zurich TMA in 2019 were most frequent to the west of the airport (see the illustration below). The pattern of infringements for the same area in 2018 had been broadly similar although less in total.
The distribution of airspace infringements recorded in controlled airspace around Zurich Airport during 2019. [Reproduced from the Official Report]
The Investigation looked back in some detail at a series of similar incursion events which had been investigated as Serious Incidents and noted that in 2016, the Swiss State Safety Regulator (FOCA) had been commissioned by the Swiss Federal Government to redesign Swiss airspace and the aviation infrastructure which FOCA was pursuing though a programme called ‘Airspace and Aviation Infrastructure Strategy Switzerland (AVISTRAT-CH)’. However, delivery of this as yet undeveloped strategy is not required until 2035 and the implementation of the first projects was not due to start until the end of 2022 with a risk that “implementation would probably extend far beyond 2035”.
The Cause of the investigated Serious Incident was attributed to the climb of the light aircraft involved into the airspace of the Terminal Control Area of Zurich Airport without the approval of air traffic control.
A Risk Factor was also identified as “the low vertical separation of 500 feet at the lower airspace boundary of the Terminal Control Area between Class G and Class C airspace".
One Safety Recommendation was made as a result of the Investigation as follows:
- that the Federal Office of Civil Aviation (FOCA) should, prior to the full implementation of the AVISTRAT-CH which is not expected before 2035, take appropriate measures including measures in the area of Safety Recommendations 466, 467, 468, 518, 519 and 520 as already issued, to ensure that the risk of a close encounter as a result of an airspace infringement is reduced.
The Final Report of the Investigation was completed on 5 July 2022 and subsequently published online on 18 July 2022. The conflict was classified as a Category ‘B’ AIRPROX.