What happened
On 8 December 2016, a private Robinson R44-Raven II helicopter was performing a non-commercial cross-country flight, departing from a private backyard in Roosdaal. The mission involved transporting three large burlap sacks, each weighing approximately 20 kg, filled with walnuts. While two sacks were secured in the rear seats, the third sack was placed on the front left seat next to the pilot.
During the initial hover phase immediately following lift-off, the aircraft experienced a rocking motion. This movement caused the unsecured sack on the front seat to shift, pressing against the vertical bar of the cyclic control. This pressure effectively blocked the cyclic movement, leaving the pilot unable to maneuver the aircraft. Consequently, the helicopter lost control and struck the ground violently on its right skid, causing the aircraft to overturn. The pilot escaped the wreckage without any injuries.
The investigation
Investigators examined the aircraft's safety restraint system, which consisted of three-point retractable seat belts. The investigation focused on the mechanics of the belt's centrifugal clutch, which is designed to lock the spool during sudden jerks. The analysis determined that while this mechanism is effective for securing human passengers, it is not suitable for cargo. Because the bags can slide underneath the belts before the retractor's locking mechanism is triggered by a high-speed rotation, the cargo remained insufficiently restrained.
Findings
- The primary cause of the accident was a loss of control at low altitude.
- This was directly triggered by a heavy bag that was not properly secured.
- The shifting weight of the bag obstructed the cyclic column, preventing necessary flight control inputs.