What happened
During a local demonstration flight near Valleyfield Airport, Quebec, an amateur-built Gilles Lélar Super Chipmunk, registration C-GLSC, experienced a catastrophic structural failure. The flight, which included the owner-pilot and one passenger, began with standard aerobatic maneuvers, including a bunt and a loop. However, while performing a complex 'Lomcevak' maneuver at approximately 4,000 feet, the aircraft entered a spin. Following a dive and an attempt to pull up, the right wing separated from the fuselage. The aircraft subsequently entered a series of rolls before impacting a cultivated field. A post-impact fire destroyed much of the wreckage, and the two fatalities were confirmed upon impact.
The investigation
Investigators examined the structural integrity of the Gilles Lélar Super Chipmunk, which had undergone significant modifications by the builder. While the engine had been upgraded to a more powerful Teledyne Continental model, the fuselage structure had been entirely redesigned. The investigation focused on the wing attachment points, specifically the bolts securing the main spars to the fuselage. Laboratory analysis revealed that the original bolts had been replaced with hardware of a significantly lower diameter and strength, providing only about 61 to 72 per cent of the original capacity.
Furthermore, the investigation looked into the flight dynamics of the Lomcevak maneuver. It was determined that the aircraft was not authorized for such aerobatic maneuvers under its existing airworthiness certificate. While no fatigue was found in the metal, the evidence pointed to an instantaneous failure caused by extreme tension.
Findings
- The aircraft was subjected to loads exceeding its structural envelope, causing the bolt securing the right lower spar to fail.
- The replacement bolts used in the wing attachment assembly were of a lower diameter and strength than the original components.
- The aircraft was performing maneuvers that were not authorized for its specific airworthiness certification.
- The high-G recovery from the dive likely generated loads that surpassed the reduced strength of the modified wing attachments.