What happened
On July 19, 2004, a Gyroflug SC 01B-160, registration HB-UCU, was conducting a VFR proficiency check flight at Grenchen Airport. The flight was intended to renew the pilot's single-engine piston class rating. After performing several maneuvers, including a go-around and simulated emergency landings, the pilot executed a landing on runway 07. The aircraft touched down approximately 50 meters past the threshold at a speed of roughly 120–130 km/h. During the landing roll, the pilot applied heavy braking to stop within the remaining runway length. However, the aircraft began to veer to the left. Despite the pilot applying maximum pressure to the right pedal, the aircraft failed to correct its direction. The aircraft exited the paved surface approximately 450 meters after the threshold, traveling across a mown field. About 300 meters later, the nose gear struck a concrete base embedded in the ground, causing the gear to collapse before the aircraft finally came to rest in a cornfield. Both occupants remained uninjured.
The investigation
Investigators examined the aircraft's braking system and the mechanical condition of the landing gear. The inspection focused on the hydraulic disc brakes, brake lines, and the control cables connecting the pedals. While the brake lines showed no leaks and the system contained no air, a detailed technical analysis revealed several mechanical discrepancies. The investigation found that the left rudder stop was incorrectly adjusted, which allowed for a longer pedal travel and potentially stronger braking on the left side. Furthermore, the right brake disc exhibited excessive run-out, which caused fluctuating brake pressure and reduced its effectiveness. Additionally, the investigation noted that the right brake required significantly more pedal force to achieve wheel lockup compared to the left side. The investigators also noted that the aircraft's tires were underinflated.