LS 1-0 ridge collision during alpine flight; speed below ridge minimum

On 19 May 2012 the pilot of an LS 1-0 was fatally injured in a collision with terrain north of the Klausenpass (Switzerland) during an alpine cross-country. The glider had launched at 11:31 from Schänis by aerotow and flown via the Engadin to Piz Linard before turning back. After about 4 h 51 min the pilot was following the rock faces of Jegerstöck and Glatten at a near-constant altitude of ~2,400 m MSL with a ground speed of only 73 to 82 km/h — well below the 87-94 km/h IAS recommended for ridge flying close to terrain. The glider struck the slope, tumbled ~300 m down the face, and was discovered 46 days later.

1. Aerotow Schänis + alpine XC: At 11:31 LT the LS 1-0 launches on aerotow from Schänis. The pilot releases at about 2,600 m after ~15 minutes, climbs to over 4,000 m in wave over the Calfeisental, reaches Piz Linard (3,400 m) by ~14:15, and then begins the return flight via Bad Ragaz and the Churfirsten back into the Glarnerland.
2. Low-speed ridge flying at ~2,400 m: On the return leg the pilot crosses from south of Linthal toward the Ortstock and then follows the rock faces of Jegerstöck and Glatten for about five minutes at a near-constant altitude of ~2,400 m MSL, close to the ridge.
3. Ground speed below ridge minimum: FLARM data in the last 20 seconds gives a ground speed of only 73 to 82 km/h on a true track of about 240°. Mountain-soaring guidance recommends a minimum airspeed of 1.45× stall speed when flying close to terrain — for this glider 87 to 94 km/h IAS. The recorded speed was well below that figure. Moderate Föhn from SE with mean wind 10 kt (gusts 20 kt) provided crosswind on the flight path.
4. Terrain contact; 300 m fall on cliff: At 16:22 LT the glider first contacts the upper face of the ridge north of the Klausenpass at about 2,425 m. It then falls over the cliffs, breaking into many small pieces scattered across a ~300 m vertical band of rock with ledges and gullies. The aircraft is destroyed and the pilot is fatally injured.
5. No technical defect; 46-day search: Examination excludes a technical cause: no abnormal accelerations in the last flight phase, no parts shed in flight, mass and CG within limits. The pilot held a glider licence since 1971 and had over 3,000 glider hours including more than 1,000 on type. Health status showed no impairment. No emergency-locator-transmitter signal was received; the wreckage was discovered 46 days after the accident by a hiker.