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A343 / GLID, en-route, north of Waldshut-Tiengen southwest Germany, 2012

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On 2 June 2012, an Airbus A340-300(HB-JMN) being operated by Swissair on a scheduled passenger flight from San Francisco to Zurich as SWR39 came very close to colliding with an ASW 20 glider (HB-1519) as it joined final approach at destination in day Visual Meteorological Conditions (VMC) whilst over Germany in accordance with its Swiss air traffic clearance. Only immediate and very positive avoiding action created minimal separation.


An Investigation was commenced after delegation of responsibility for it was made by the German BFU to the Swiss Accident Investigation Board (SAIB). Sufficient recorded data relevant to the Investigation was available from ATC radar recordings.

It was established that, with the Airbus passing 4700 feet Altimeter Pressure Settings for 4000 feet at 248 knots and about to join the Instrument Landing System (ILS) Localiser for runway 14 at Zurich, the augmenting crew member observing the approach from the central supernumerary crew seat suddenly saw a glider at the same altitude on a collision course. The operating crew were immediately alerted and the First Officer, designated PF took avoiding action. The Airbus was flying in accordance with its clearance from the Zurich APP controller but the glider was found to have entered the Class 'C' TMA in which the conflict occurred without permission.

Recorded radar data showed that "a pronounced avoidance manoeuvre" by the A340 was made 5 seconds prior to the closest proximity and had involved "a maximum bank angle of 36 degrees to the left and an increase in attitude to approximately 5 degrees, which generated a normal acceleration of 1.6 g". It was found that 13 seconds before the closest proximity, the glider had begun "an abrupt right-hand turn as an avoidance manoeuvre". The two aircraft subsequently "passed at approximately the same height at a lateral distance of approximately 260 metres" (850 feet) ten seconds after the A340 had initiated avoiding action. The situation is depicted on the diagram below included in the Official Report.

Proximity of the two aircraft showing airspace violation by the glider (reproduced from the Official Report)

It was considered that the recorded flight paths of the two aircraft over the less than 15 seconds which had elapsed from the initiation of avoiding action until the position of closest proximity showed that "neither avoidance manoeuvre in isolation was decisive in avoiding a collision". It was also concluded that the dynamics of this encounter "clearly indicate(d) that that there are few opportunities for action to avoid a collision (when) in a relatively slow moving aircraft."

In respect of the danger posed to large transport aircraft by airspace incursions undetectable to radar surveillance or Airborne Collision Avoidance System (ACAS), it was observed that it was very difficult for the crew of a commercial aircraft to visually detect a potentially conflicting glider without prior warning since "it is almost impossible to detect small objects with low contrast to their background". It was considered that in the investigated incident, "detection of the glider was certainly helped by the fact that it was turning and that its bank angle changed abruptly, as humans can detect moving objects better than stationary ones". It was concluded that "the role of the observing pilot is likely to have been decisive."

After the glider pilot had failed to file a report or come forward in response to appeals from the Investigation, he was eventually traced and was reportedly cooperative thereafter. He stated that his airspace incursion had been intentional because "while circling….I needed some height for the onward flight." It was found that after landing at the Bohlhof glider airfield (from which he had earlier taken off) following the incident, the glider pilot "did not report the serious incident to the authorities or the club management". However, when, a few days later, "the flight data of all aircraft which had taken off from or landed at Bohlhof…on 11 August 2012 were inspected by the club management", he stated that he had "then informed the club management that he had been involved in the serious incident". It was found that he had been a member of the Bohlhof Gliding Club since 1968 "and was familiar with the airspace structure around the airfield". An analysis of the flights he had made between 15 June 2011 and 11 August 2012 showed "that he had flown into the (Zurich TMA controlled airspace) without verifiable clearance on at least five flights".

Further Reading