On June 18, 2006, at 0848 central daylight time, an amateur-built Good RV-6A airplane, N86CG, was destroyed and an amateur-built Turner RV-8 airplane, N68LT, was substantially damaged during a mid-air collision at the Illinois Valley Regional Airport (VYS), Peru, Illinois. After the collision the RV-6A descended and impacted terrain. The RV-8 landed successfully at VYS. Both airplanes were part a four aircraft formation preparing to land at the time of the accident. The flight was being conducted under 14 CFR Part 91 without a flight plan. Visual meteorological conditions prevailed. The pilot of the RV-6A sustained fatal injuries. The pilot of the RV-8 was not injured. Both airplanes departed Poplar Grove Airport (C77), Poplar Grove, Illinois, about 0815. The pilots were members of the RV Blackhawk Squadron and were flying to VYS for the Illinois Valley Air Show. The group was scheduled to perform in the air show later that day. The pilot of the RV-8, who was the lead airplane in the formation, reported that the flight of four was established southbound over the approach end of runway 18 when he initiated an overhead recovery for landing. He stated that he pulled up and started a turn to enter downwind. He reported that shortly after starting his turn he felt the impact of the other airplane. He was able to maintain control and subsequently landed on runway 36. A ground-based witness reported that the four airplanes flew over his position northbound in a diamond formation at 800 - 1,000 feet above ground level (agl). He noted that the formation appeared "evenly spaced and steady." The formation proceeded to make a descending turn. As the formation was established southbound, about 200 feet agl, the lead airplane executed a climbing left turn away from the other airplanes. Approximately two seconds later the second airplane also began a left climbing turn. The witness reported that this airplane "appeared to turn and climb much more aggressively than the lead aircraft." Prior to completion of the turns, the witness stated the second airplane "merged with the lead aircraft from below and from the left." He noted seeing debris separate from the airplanes due to the collision. The second airplane subsequently entered a "near vertical, slow spiral descent in a nose down attitude." A second ground-based witness stated that the lead airplane "peeled off up and to the left," followed within 5 seconds by the second airplane in the formation. He reported that the second airplane's flight path subsequently placed it under the lead airplane's left wing. The second airplane's nose and right wing collided with the lead airplane's left wing. Post accident inspection of the Good RV-6A airplane, N86CG, did not reveal any anomalies associated with a pre accident failure. All flight control surfaces, with the exception of the right flap, remained with the airplane. Separation of the flap was consistent with impact damage. Control continuity was confirmed from the rudder and elevator to the cockpit area. Breaks in the aileron control system were consistent with impact and overload failures. The pilot of the Turner RV-8 airplane reported no failures or malfunctions with the aircraft prior to the accident. Paint transfer marks consistent with the color of the trim on the RV-6A were observed on the left wing of the RV-8 during a post accident inspection. Weather conditions recorded by the VYS Automated Surface Observing System (AWOS), at 0845, were: Winds from 220 degrees at 10 knots; 10 statute miles visibility; overcast clouds at 9,500 feet above ground level; temperature 22 degrees Celsius; dew point 20 degrees Celsius; altimeter 29.86 inches of mercury.