What happened
On July 7, 2007, a locally based pilot was conducting an aerial photography flight in an amateur-built 601XL ultralight, identified as 85-PK. The flight departed from the Montaigu aerodrome with one passenger on board. While cruising at approximately 3,000 feet and a speed of 180 km/h, the pilot initiated a descent. As the aircraft accelerated toward 200 km/h, a loud thud and a snapping sound were heard beneath the cockpit.
The pilot reported that upon pulling back on the control stick—approximately one-third of the total travel—the left wing folded upward until it contacted the canopy. This structural failure caused the aircraft to enter a continuous rolling motion. To prevent a total loss of control, the pilot deployed the aircraft's emergency parachute. The descent lasted roughly one minute, and the aircraft reached the ground with a low vertical velocity. The aircraft was destroyed in the accident.
The investigation
Investigators examined the wreckage to determine the cause of the wing failure. The inspection revealed that the left wing root was deformed and that the spar had failed due to an upward static bending force.
While the aircraft was a kit-built version of the Zenair CH 601 XL, the components were sourced from a Polish manufacturer unrelated to Zenair. Although the flight documentation for both the original design and the kit specified a flight envelope between -2 and +4 g, investigators could not verify if this specific aircraft met those structural specifications. The pilot noted a habit of performing maneuvers that frequently reached load factors of approximately 3 g, as recorded by an onboard accelerometer; however, the exact load factor at the moment of failure could not be determined because the device had been reset following the event.
Findings
- The primary cause of the accident was the execution of maneuvers exceeding the structural strength of the wing.
- The left wing spar failed under upward bending stress.
- The aircraft's structural integrity relative to the manufacturer's stated load limits had not been verified.