What happened
On 4 August 2023, an Extra NG (registration SP-HMM) was performing a planned aerobatic flight near the Pobiednik aerodrome (EPKP) in Poland. The pilot, accompanied by a passenger, was executing several aileron rolls at an altitude of approximately 1000 m AGL. During level flight following a completed roll, the cockpit canopy unexpectedly opened. The force of the airflow caused the canopy to break free from its opening limit strap, resulting in the canopy striking the upper surface of the starboard wing. The pilot performed an emergency landing back at the departure airfield. While the aircraft sustained damage to the canopy frame and the wing surface, there were no injuries to the pilot or the passenger.
The investigation
The PKBWL investigation involved technical analysis and consultation with the German Federal Bureau of Aircraft Accident Investigation (BFU) and the aircraft manufacturer, TCH. The investigation focused on the mechanical integrity of the locking mechanism and the sequence of the canopy release. Investigators examined the damage to the canopy's pawls, hinges, and the adhesive bonds of the frame. The inquiry also reviewed the pilot's statements and compared the event to a previous similar incident involving the same aircraft in March 2022.
Findings
- The investigation determined that the cockpit locking mechanism was functioning properly and that aerodynamic forces alone were not sufficient to unlatch the mechanism if it were fully secured.
- It was found that the canopy locks may not have been fully engaged and secured prior to the flight.
- The design of the latching system technically allows for partial engagement, which does not provide a positive indication of a secure lock to the pilot.
- The investigation noted that aerodynamic forces and vibrations during high-velocity maneuvers could have increased the load on partially engaged locks, causing them to displace into the open position.
- It was noted as a possibility that the passenger might have inadvertently loosened the locks while attempting to stabilize themselves during maneuvers.
- The damage to the canopy frame and the starboard wing was a direct result of the impact caused by the canopy after the limit strap failed.
Safety action
Following the occurrence, the manufacturer (TCH) implemented several preventive measures:
- The Pilot's Operating Handbook (POH) was revised to clarify pre-flight check procedures and the description of the canopy locking process.
- New in-cockpit legends were introduced to clearly indicate the correct "Locked" position for the handle.
- The cockpit canopy locking mechanism on the involved aircraft was modified with a change in pawl contour and the installation of an additional spring to increase hold-down force.
- The manufacturer has implemented these improved locking systems as standard equipment on newer aircraft production series.