Summary
On 24 April 2020, a privately owned DG-400 glider (registration HB-2068) experienced an engine malfunction during a cross-country flight, leading to a forced landing in a rapeseed field near Kölliken, Aargau. The pilot was uninjured, and the aircraft suffered minor damage to the tailwheel, ailerons, and flaps.
Incident Details
The pilot, a Swiss national born in 1990 holding a Sailplane Pilot Licence (SPL) issued under EASA, had planned a flight from Courtelary (LSZJ) covering a declared FAI triangle of over 600 km. After more than 8.5 hours of flight, he began circling in weak lift northeast of Kölliken around 18:30 LT at 650 m AMSL, climbing to 825 m AMSL over 16 minutes. He then lost that altitude in about 6 minutes. At approximately 200 m above ground (430 m AMSL), he extended the retractable engine over a potential landing field, intending to return to Courtelary under power.
After successful engine start, the engine only reached less than 5000 rpm, insufficient for climb (takeoff rpm is 6200). After brief manipulation of the throttle and choke, the pilot decided to land on the preselected field. With the engine still extended, the glider exhibited a lower sink rate than expected. On final approach with flaps in landing position, he briefly deployed full airbrakes. The glider touched down short of the intended field, and the left wingtip contacted rapeseed plants, causing the glider to yaw violently around its vertical axis. The tailwheel, ailerons, and flaps were damaged. The pilot exited unassisted and uninjured.
Aircraft and Pilot Information
The DG-400 (serial year 1982, manufactured by DG Flugzeugbau GmbH) is a self-launching glider with a Rotax 505 engine. It was flown in the 17 m wingspan configuration. The pilot had 2687 total flight hours, with 617 hours on type. Pre-flight inspection revealed no anomalies; the engine functioned normally during takeoff and climb.
Investigation and Findings
The Swiss Transportation Safety Investigation Board (STSB) investigated the incident. Post-landing engine tests reached 5500 rpm, but the pilot did not advance the throttle to full power. It is considered plausible that reduced power before landing may have been caused by particles in the carburetor, possibly originating from a metal fuel can used shortly before the incident; a plastic can has since been used.
Weather conditions: dry air, extensive cirrus clouds, wind from west at 5 kt. Sun azimuth 274°, elevation 14°. The pilot initially did not report the incident to STSB, believing it not required, but later reported via the EASA Aviation Safety Reporting portal.
Analysis and Conclusions
The STSB analysis noted that with cirrus clouds and low sun angle, thermal lift was unlikely after 18:46 LT, making engine use necessary for the 75 km return to Courtelary. The engine start attempt at 200 m AGL, even above a landing field, was late relative to the manufacturer's recommendation in the DG-400 flight manual (Chapter 4.4), which advises not to extend the engine below 500 m AGL. The pilot's decision to focus solely on landing after insufficient engine power was deemed prudent and safety-conscious, potentially avoiding worse outcomes such as loss of control. The misjudgment of the glide path, resulting in touchdown short of a usable field over 200 m long, was understandable given the time pressure. The contact with rapeseed plants created a force that induced a yaw rotation which opposite control inputs could not counteract.
The STSB referenced previous safety information from German and Swiss investigations highlighting risks associated with retractable engines and the importance of proper maintenance and pre-flight preparation.