Introduction
On 18 February 2021, a Piper PA34-200T Seneca II, registered as T7-RAR, was involved in an accident at Rorschacher Bucht, approximately 1.3 nautical miles west of the threshold of runway 10 at St. Gallen-Altenrhein Airport (LSZR). The aircraft was owned and operated by Akzenta International SA of Chiasso, Switzerland. The pilot, a German national born in 1951, held a Private Pilot Licence (PPL(A)) issued by the German Federal Aviation Office under EASA regulations.
Flight History
The flight departed Locarno Airport (LSZL) at 09:47 UTC under Instrument Flight Rules (IFR) with a destination of St. Gallen-Altenrhein. The crossing of the Alps proceeded without incident. While approaching waypoint SITOR, the pilot requested an RNP approach to runway 10. Air traffic control cleared the aircraft to descend to Flight Level 80 and directed it to waypoint ZR695. At 10:19 UTC, the pilot contacted Zurich Arrival and arranged for an RNP approach with a full stop landing. Clearance was given to descend to 6000 ft AMSL, with the controller indicating 20 nautical miles remaining to landing.
Accident Sequence
At 10:23:13 UTC, while at 9000 ft AMSL and 5 nautical miles from ZR695, the pilot inquired about the next waypoint. The controller offered radar vectors to intercept the approach instead of continuing with own navigation. Shortly after, the pilot was cleared: "Descend to 5000 ft, turn right heading 070, cleared for the RNP approach runway 10, report established." The aircraft crossed the Final Approach Fix (FAF) at 6100 ft AMSL (the charted altitude at FAF is 5000 ft) with a ground speed of 142 knots. At 10:27:48 UTC, the pilot confirmed being established on the approach. The frequency was switched to St. Gallen Tower. At 10:28:17 UTC, a transmission containing only engine and breathing sounds lasting 5 seconds was recorded. The controller called the aircraft, and at 10:28:55 UTC landing clearance was issued, along with instructions for the missed approach procedure. At the time of clearance, the aircraft was 3.7 nautical miles from the threshold at 3400 ft AMSL with a ground speed of 133 knots. The last radar recording occurred at 10:30:12 UTC, 1.5 nautical miles from the threshold and 100 ft above Lake Constance. The pilot, seeing the water surface unexpectedly through the fog, pulled back on the controls. The aircraft impacted the water, severing the right main landing gear leg. At 10:30:38 UTC, a transmission of splashing water sounds lasting 12 seconds was recorded. Subsequent calls from the controller went unanswered. The pilot exited the aircraft, which sank to the lake bed at a depth of about 90 meters. Holding onto the floating right main landing gear leg, the pilot was found by a fisherman approximately one hour later in a severely hypothermic condition but survived due to timely rescue.
Weather
Dense ground fog was present over the St. Gallen-Altenrhein area, with a fog top around 2000 ft AMSL. The reported runway visual range was 250 meters and vertical visibility was 200 ft. Above the fog, conditions were clear with unlimited visibility. The pilot was aware of the weather and intended to conduct the RNP approach for training, with a plan for a second instrument approach in St. Gallen-Altenrhein or a diversion to Friedrichshafen in case of a go-around.
Pilot's Account
The pilot stated that the glide path indicator on the RNP approach displayed the aircraft well above the glide path throughout the approach until impact. In an effort to reach the glide path as soon as possible, he descended steeply without cross-referencing other instruments. He did not observe the decision altitude for the approach. The aircraft was being manually controlled. Comparison of the RNP vertical profile and radar data showed that the pilot did not overfly SITOR at 5000 ft AMSL as possible; his altitude at SITOR was 6200 ft. He then descended at an average rate of 1250 ft/min and intercepted the glide path at approximately 2500 ft AMSL, 2.6 nautical miles from the threshold, continuing the descent without adjustment.
Investigation
As the accident site in Lake Constance is in international waters, the Republic of San Marino (the state of registration) was originally responsible for the investigation under ICAO Annex 13. However, on 10 March 2021, San Marino delegated the investigation to the Swiss Transportation Safety Investigation Board (STSB) in accordance with Article 5 of the Annex. The investigation is classified as a summary investigation under Swiss regulations.