The pilot reported that while in a descent from 16,000 feet, at 1,500 feet per minute, slowing from 190 knots indicated airspeed to 160 knots, the airplane encountered extreme turbulence. The pilot reported one hard jolt up/down followed by about 15 seconds of light turbulence then one final hard jolt similar to the first. The weather was visual conditions and no turbulence was encountered prior to or after the event. A postflight examination of the airplane revealed that the extreme turbulence encountered resulted in substantial structural damage to both wings spars.

The pilot reported there were no pre-impact mechanical failures or malfunctions with the airframe or engine that would have precluded normal operation.