What happened
Two separate incidents involving APM3 and APM30 aircraft occurred within two weeks in August 2012.
On August 7, 2012, an APM30 with registration F-HADO departed Thouars for a VFR flight to Guéret. Approximately 40 minutes into the flight, while cruising at 2,000 feet near Le Blanc, the canopy detached from the aircraft. The pilot maintained control and performed a precautionary landing at Le Blanc. The pilot noted that due to high temperatures, the canopy had only been closed during the final approach, and while the handle position was visually checked, the engagement of the locking hook was not verified.
On August 20, 2012, an APM30 with registration F-HOUF departed Dinard for Aubigny. During cruise at FL 055 near Blois, the pilot noticed the canopy locking handle had rotated approximately 30 degrees. After resetting the handle, a cracking sound was heard ten minutes later, and the canopy separated from the aircraft. The pilot managed to maintain control and landed at Blois.
The investigation
The investigation examined the canopy locking systems of both aircraft. It was established that the locking hook may fail to engage even if the handle appears to be in the closed position. This occurs if the canopy is closed without first moving the handle to the "open" position. If the handle is not cycled from the open position, the hook rests against the left side of the pin without hooking it, resulting in an ineffective lock.
Testing confirmed that during an incorrect lock, the handle can rotate freely by about 30 degrees, whereas a correct lock requires physical effort to move the handle from the closed position. In the case of F-HADO, abnormal wear and friction marks on the front and right edge of the hook indicated that the canopy had been closed without the handle in the "open" position on multiple occasions.
Findings
- The primary cause of both incidents was the failure to detect an incorrect canopy lock.
- The decision to close the canopy immediately before takeoff contributed to an insufficient verification of the locking hook position.
- The locking mechanism is susceptible to improper engagement if the handle is not properly cycled from the open position to the closed position, as specified in the flight manual.