What happened
On 11 December 2011, a Rainbow Aircraft Cheetah, registered OO-G29, was conducting a training flight near the EBHN airfield in Hoevenen, Belgium. The flight, which included a pilot and one passenger, was intended as an introductory flight. After departing from Runway 15 and climbing to 600 feet, the aircraft entered the downwind leg of the circuit.
During this maneuver, the aircraft's windscreen suddenly broke apart. The pilot reported that the elevator controls became ineffective, and the aircraft began a rapid descent. Despite attempts to use the ailerons to steer toward the airfield and applying full throttle, the pilot was unable to maintain altitude. The pilot eventually selected a reed field for an emergency landing. The impact caused heavy damage to the aircraft, including the loss of the landing gear and a broken propeller blade. The pilot sustained a serious injury (a broken vertebra), while the passenger was uninjured.
The investigation
Investigators examined the wreckage and the windscreen, which had fractured into four pieces. While the occupants initially suspected a bird strike, no evidence of an external impact was found. The investigation revealed that the windscreen's installation did not follow the manufacturer's assembly manual. Specifically, the required rubber seal (PP110) was missing, and silicone sealant had been used instead.
Analysis of the attachment points showed friction wear, indicating that the windscreen was moving against the airframe. The absence of the rubber seal removed a critical vibration dampener and stress buffer, likely leading to the development of cracks. It was also noted that light cracks had been observed on the windscreen as early as September 2011.