What happened
On July 1, 2020, a Guimbal Cabri G2 helicopter, registration HB-ZDQ, was conducting a flight training mission near Vaulruz, Switzerland. The flight, part of a private pilot training program, involved an instructor and a student pilot. The objective of the flight was to practice altitude maintenance and demonstrate the aircraft's performance near its maximum speed (Vne) at an altitude of approximately 5,500 feet.
During the flight, the crew began a descent toward Bulle to perform high-speed maneuvers. As the aircraft reached an indicated airspeed of 110 knots, the single-piece plexiglass canopy suddenly shattered. The sudden depressurization and high relative wind caused significant disruption within the cockpit. Debris from the canopy entered the cabin, and the force of the wind stripped the headsets and goggles from both occupants. One headset was partially pulled out of the cockpit through an unsecured door but remained attached by its communication cables.
The instructor, using a spare pair of medical glasses, managed to reduce the airspeed and performed an emergency landing near Vuadens. Both the instructor and the student sustained minor injuries to their faces, hands, and legs. The impact of the canopy failure also triggered the aircraft's emergency locator transmitter.
The investigation
Investigators examined the structural integrity of the Guimbal Cabri G2 canopy, which consists of 2mm thick plexiglass secured only around its perimeter. The investigation focused on the aerodynamic stresses applied to the canopy during high-speed operations.
Technicians identified that a suction cup, intended for mounting an onboard camera, had been attached to the canopy. While such devices are common for mounting equipment, this specific installation was not approved by the manufacturer and introduced additional structural stresses that weakened the plexiglass.