Background
On 31 May 1998, a Hughes 269 B helicopter was involved in an accident near Plettenberg, North Rhine-Westphalia, Germany. The helicopter was US-registered and operated by its owner, who served as copilot during the flight. The pilot-in-command (PIC) was the responsible pilot for the flight, which was a private sightseeing trip.
Flight and Accident
The helicopter departed at 13:56 local time from the grounds of a company where it was stored in a hangar. The flight proceeded to an area south and east of Plettenberg. A witness observed the helicopter performing several curves and course changes in close proximity. Shortly before the accident, the witness heard the helicopter descending into a forest but did not see the crash. The witness alerted emergency services, leading to the discovery of the seriously injured pilots approximately one hour after the accident. The helicopter was destroyed, and the forest sustained damage.
Investigation
The German Federal Bureau of Aircraft Accident Investigation (BFU) examined both operational and technical aspects. The PIC described an uncontrollable flight condition that began at 400–600 ft above ground level with rotations around the vertical axis, ending in an autorotation with the throttle closed and impact with a high forest. The copilot reported memory loss for the entire day and provided no account. GPS data confirmed the witness's observations of maneuvers but did not show the reported "rounds" before the crash. A thorough technical inspection found no evidence of mechanical failure; the engine functioned correctly. The investigation also uncovered irregularities and suspected violations of aviation regulations. Initially, the owner was thought to be the PIC, but later evidence indicated the less experienced pilot (80 flight hours on helicopters) was the PIC and was flying from the left seat.
Probable Cause
The accident was likely due to one or more control errors by the pilot-in-command, who flew low-speed, tight turns that exceeded the helicopter's performance capabilities. This led to a decrease in rotor rpm, resulting in an uncontrolled rotation around the vertical axis. The more experienced copilot attempted to recover by initiating an autorotation, but the low altitude prevented a successful outcome.