What happened
On July 22, 2021, an Alisport Silent 2 Electro ultralight glider, registered D-MANS, was performing a private flight in the Rhone valley near Conthey, Switzerland. After departing from Thun airfield earlier that day, the aircraft was cruising at approximately 1700 m AMSL near the Sion airfield. An eyewitness observed the glider's nose pitch upward, followed by a turn. Shortly after, the aircraft entered a near-vertical descent, impacting a steep slope at 1630 m AMSL. The impact resulted in one fatality and the total destruction of the aircraft.
The investigation
Investigators examined the wreckage and flight data, finding no evidence of mechanical or technical failures in the aircraft's electric propulsion system or airframe prior to the crash. Meteorological conditions at the time were characterized by weak to moderate thermal activity and clear visibility. The investigation also looked into the pilot's medical status, noting that while the pilot held a valid medical certificate, an autopsy revealed long-term use of medication that could affect the ability to operate machinery. Furthermore, the investigation assessed the hazards present at the crash site, specifically regarding the risks posed by high-voltage electric batteries and potential ballistic parachute systems to emergency responders.
Findings
Analysis of the flight path and eyewitness accounts indicates that the accident was caused by the aircraft flying below its minimum speed during a turn, which induced a stall. Due to the proximity of the terrain, the pilot was unable to recover the aircraft from this flight condition. Additionally, the investigation found that emergency services lacked immediate access to critical information regarding hazards at the site, such as the presence of high-voltage components or ballistic parachute systems, because such details were not readily available in the aircraft's markings or accessible rescue cards.
Safety action
Following the accident, the STSB issued several safety recommendations and advice:
- Safety Recommendation No. 596: Urges ICAO to establish a database for emergency services to identify aircraft hazards without delay.
- Safety Recommendation No. 597: Recommends that the Federal Office of Civil Aviation (FOCA) provide a similar hazard database for aircraft operating in Switzerland.
- Safety Recommendation No. 598: Suggests that the COSPAS-SARSAT Programme include information about ballistic parachute systems in the coding of 406 MHz ELTs.
- Safety Advice No. 57: Advises all operators to use the "Other information" field in ATC flight plans to disclose the presence of hazardous equipment, such as electric propulsion or parachute systems, to assist search and rescue efforts.