Summary
On 21 December 2016, a Pilatus PC-6/B2-H4 aircraft, registration EC-IBY, operated by Air Compluto, was involved in a serious incident at Buochs aerodrome (LSZC) during an approach in meteorological conditions below the minima for Special Visual Flight Rules (SVFR). The aircraft was on a ferry flight from Valence (LFLU), France, to Buochs, Switzerland, for maintenance. Both crew members were uninjured, and the aircraft sustained no damage.
Flight History
The aircraft was stationed at Lillo aerodrome (LELT) in Spain, where it was used for parachute dropping. For the ferry flight to Pilatus Aircraft Ltd in Buochs, the operator appointed two pilots: a commander in the left seat and a safety pilot. The commander had 446 hours on type; the safety pilot had 1520 hours. The crew used outdated navigation charts from 2007 and 2010, supplemented with downloaded approach charts.
On 13 December 2016, EC-IBY flew from Lillo to Sabadell, Spain, and the next day to Valence, France. The final leg to Buochs was delayed one week due to low stratus clouds over central Switzerland. On the morning of 21 December, weather appeared to improve, with a 40% chance of CAVOK forecast for the afternoon. The crew filed an ICAO flight plan with a departure time of 13:15 LT and arrival at 15:00 LT.
EC-IBY departed Valence at 13:25 LT. Weather above clouds was reported as perfect. The crew used GPS navigation and the safety pilot occasionally checked position via a mobile phone GPS.
At 14:49:19 LT, the crew contacted Buochs tower, reporting 15 NM from the aerodrome at FL 81 in descent. The air traffic controller (ATCO 1) reported wind 210°/4 kt, runway 24 in use, visibility 4 km in mist, overcast ceiling at 600 ft AGL, temperature 2 °C, dew point 1 °C, and QNH 1029 hPa. ATCO 1 informed the crew that the aerodrome was below SVFR minima. The crew stated they were unfamiliar with the surroundings and asked about descent possibilities. ATCO 1 advised there was no chance to get below the clouds and pointed out a possible hole in the clouds southeast of the control zone.
The crew remained at 6000 ft QNH. Over the next several minutes, ATCO 1 reminded the crew that any descent would be at their own discretion, considering the challenging terrain. At 14:55:33 LT, the crew reported over the aerodrome at 6000 ft. ATCO 1 again mentioned the southeast corner as the best chance. The crew indicated they would attempt, though conditions did not look favorable.
At 15:01:25 LT, the crew announced they would return to the departure point. ATCO 1 confirmed and instructed them to report leaving the control zone and set transponder code 7000. At 15:03:23 LT, a brief Spanish conversation was recorded; the crew later said they were discussing a hole in the clouds. At 15:03:34 LT, they reported locating a small hole for descent. ATCO 1 instructed them to maintain VFR in VMC and report when below the clouds. The crew acknowledged. ATCO 1 believed the aircraft was near Brunnen, but his radar showed EC-IBY to the south.
Weather Conditions
According to ATCO 1, the weather at Buochs that morning had a very low ceiling and poor visibility. Fog near Beckenried lifted slightly towards midday but then stalled, never clearing. There were isolated spots with faint blue sky. The reported ceiling was overcast at 600 ft AGL with visibility 4 km in mist. These conditions were below SVFR minima.
Aftermath
The aircraft returned to Valence without further incident. No injuries to persons or damage to the aircraft occurred. The Swiss Transportation Safety Investigation Board (STSB) investigated the serious incident, classified as a dangerous approach to terrain at meteorological conditions below SVFR minima.