DG-808 and DG-500 pass at 25 m: each crew focused elsewhere

A DG-808 C and a DG-500/22 ELAN passed at about 25 m horizontal and a few metres wing-tip to wing-tip near St. Moritz; no injuries or damage. Both were winch-launched from Samedan and met on near-reciprocal tracks at about 3,200 m MSL. The DG-808 C pilot was tracking a Duo Discus passing safely below-left; the DG-500's instructor was pointing out the hard-to-see Corvatsch cableway wires ahead-left. Neither crew saw the opposing glider against the bright cloud and snow background until the last moments; both then simultaneously rolled left. FLARM testing later found the DG-500's transmit and receive insufficient.

1. Cruise NE on Corvatsch N slope: At about 17:01 LT on 16 June 2014 the DG-808 C (HB-2461, solo pilot) was cruising north-east along the north slope of Piz Corvatsch at about 3,200 m AMSL at GS 149 km/h. The DG-500/22 ELAN (HB-3097, pilot and instructor) was cruising south-west over the north flank of Piz da Staz at about 3,100 m AMSL at GS 135 km/h — near-reciprocal tracks. Both had launched on winch from Samedan earlier that afternoon as part of the annual SFVS alpine introduction course. A third glider, a Duo Discus, had just overtaken the DG-500 at 17:01:15 LT and was ahead-right slightly below.
2. DG-808 pilot focused on Duo Discus: The DG-808 C pilot's FLARM had warned of a slightly lower glider on a converging track. Seeing the Duo Discus, he made a slight right course correction toward the north-west flank of Piz Surlej to give it clearance. He then watched the Duo Discus pass safely under his left wing — focusing his attention on that target.
3. DG-500 crew focused on cableway wires: The DG-500 crew had already spotted the Duo Discus ahead-right and slightly below. The instructor was pointing out to the front-seat pilot the hard-to-see free-hanging cables at the mountain station of the Corvatsch cableway, visible ahead-left — attention drawn to a ground-based obstacle just before the encounter.
4. DG-500 FLARM TX/RX degraded: Both gliders were equipped with FLARM, but neither crew received a warning of the opposing aircraft. The DG-500's FLARM had been flagged in June 2013 for limited receive range, and the transmit range was judged limited by other pilots' observations. A new dipole antenna had been fitted in the winter of 2013/14 but the range was never re-tested. After this incident bench testing found both the transmit power and the receive sensitivity insufficient. The DG-808's FLARM showed no defects.
5. Bright cloud + snow background: The two gliders were closing against a background of bright clouds and snow fields, reducing the contrast needed to acquire each other visually.
6. Late mutual sighting at ~25 m: When the Duo Discus disappeared under his left wing the DG-808 pilot looked up and saw a second glider directly ahead at the same altitude, slightly to the left, closing fast. At the same instant the DG-500's pilot, on a routine forward scan, saw a glider at the same altitude slightly to the right; the instructor saw it simultaneously.
7. Sim. left turns; clear by metres: Both crews instinctively rolled left at almost the same moment. The DG-808 pilot consciously watched the DG-500's right wingtip relative to his own right wingtip to check for a collision; the wings passed within a few metres. The reconstructed flight paths show a horizontal fuselage separation of about 25 m (±5 m) at the closest point. All three gliders subsequently landed normally at Samedan.