What happened
On May 3, 2004, a Cap 231 EX aircraft, registration HB-SBC, was conducting a training flight at Granges Aerodrome as part of a national selection process for the Swiss aerobatic team. While performing maneuvers under the supervision of an instructor, the pilot reduced engine power to better hear feedback. Upon attempting to restore full power, the pilot found the throttle unresponsive.
After performing standard emergency checks—including verifying the magneto, fuel selector, mixture, and electric pump—the engine continued to lack power. The pilot attempted to manage the descent by performing two 3-60 degree left turns to lose altitude. However, the pilot found the aircraft too low and too fast to land safely on the runway without overshooting a nearby canton road. To avoid an overshoot, the pilot executed a right turn and eventually decided to force the aircraft into the ground to prevent a stall. The impact was severe: the left landing gear detached, the right gear collapsed, and the propeller struck the ground and broke. The aircraft came to rest in a grassy area approximately 50 meters from the runway.
The investigation
SUST investigators examined the engine and the exhaust system to identify the source of the power loss. During a detailed inspection of the "Gomolzig" silencer, technicians discovered that a perforated tube located within the expansion chamber had fractured and oxidized. A broken piece of this tube had shifted toward the exit of the expansion chamber, effectively blocking the exhaust gas flow.
The investigation also reviewed the pilot's operational decisions. It was noted that the pilot was highly experienced and was flying a physically demanding training program, which may have contributed to fatigue. The investigation also looked into the flight path, noting that the pilot's attempt to avoid the nearby road led to a high-energy impact.