The pilot reported that there were no observed anomalies with the left wing prior to the flight. During the flight, which was conducted as a local parachute operation, the pilot performed a descending turn. The left wing’s aileron bound when the pilot attempted to level the bank. The pilot declared an emergency. The pilot and a passenger were able to exert enough force to the control wheel to regain control of the airplane and land safely. An on-scene examination of the airplane revealed damage to the left wing flap and aileron consistent with an overload event; however, the investigation could not definitively pinpoint the cause of the damage. Probable Cause: Undetermined.