B738 / AS25, en-route, near Frankfurt Hahn Germany, 2013

B738 / AS25, en-route, near Frankfurt Hahn Germany, 2013

Summary

On 25 April 2013, the experienced pilot of an en-route motor glider which was not under power at the time and therefore not transponding observed a potentially conflicting aircraft in Class 'E' airspace near Frankfurt Hahn and commenced avoiding action. Although the glider was within their field of view, neither of the pilots of the other aircraft, a Boeing 737 in a descent, was aware of the proximity of the glider until it passed them on an almost parallel opposite-direction track 161 feet below them at a range of 350 metres as their aircraft was passing approximately 6,500 feet QNH.

Description

On 25 April 2013, a Boeing 737-800 being operated by Ryanair on a scheduled international passenger flight from Alghero, Sardinia to Frankfurt Hahn in Class 'E' airspace in day VMC and descending towards its destination when it passed very close to a previously unseen ASH 25 motor glider on an almost parallel opposite track as it was descending through approximately 6,500 feet. The encounter was reported to ATC and it was subsequently found that the two aircraft had come within 350 metres laterally and 161 feet vertically of each other.

Investigation

An Investigation was carried out by the German BFU. Relevant data from the 737 QAR and from the NVM of the Motor Glider's GPS were successfully downloaded and useful recorded radar data were available from both civil and military ATC Units. However, it was noted that although powered aircraft in Class 'E' airspace are required to have an activated transponder when flying above 5,000 feet QNH or at more than 3,500 feet agl, the motor glider involved was unpowered during the encounter and so had not been visible to ATS units as a secondary radar target.

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