What happened
On 18 March 2022, an Extra NG aircraft, registration SP-HMM, was performing aerobatic maneuvers at the Kraków-Pobiednik aerodrome. During a previous flight on the same day, the crew had noted unusual vibrations and sounds, which they initially attributed to the engine. After a ground inspection revealed no engine irregularities, the crew proceeded with a third flight.
While the aircraft was accelerating to approximately 350 kph at an altitude of 4,000 ft AGL, the cockpit canopy suddenly released from its locks. The canopy swung on its hinges, struck the right upper wing skin, and broke apart. Debris from the canopy frame detached and fell to the ground. The pilot immediately reduced speed to 200 kph and performed an emergency descent, landing the aircraft safely at the aerodrome. The pilot sustained one minor injury (a facial cut), while the passenger remained uninjured.
The investigation
The PKBWL investigation examined the aircraft's locking mechanism, the cockpit structure, and the flight history. Investigators inspected the canopy hinges, the pawl locking system, and the composite frame. The investigation focused on why the canopy released despite the pilot's declaration that the mechanism had been properly locked before takeoff.
Findings
- The investigation identified that the rear fitting of the canopy locking system had loosened, creating a clearance between the fitting and the portside of the fuselage.
- This clearance, combined with a probable crack in the carbon-fiber canopy frame, led to a significant loss of structural stiffness.
- Vibrations caused by the loss of canopy frame stiffness led to the pawls unlocking, which ultimately caused the canopy to detach from the aircraft.
- Contributing factors included a potential crack in the frame occurring prior to the flight and the aircraft accelerating to a high speed near its maximum operating velocity (VNE).