Background
Prior to departure, the flight crews of two Shorts Brothers SD-360-300 turboprop airplanes decided to join up in flight to take video and still pictures of each other. The aircraft involved were N3735W and N372AC.
Collision
While flying in formation, the crew of N3735W announced over the radio that they would turn right, toward N372AC, and descend. During the turn, the left wing of N3735W impacted the left wing and engine of N372AC.
Aftermath for N372AC
After the collision, N372AC rolled to the left and pitched down significantly before the flight crew regained control. The aircraft was losing hydraulic fluid and eventually experienced a complete hydraulic system failure. An emergency landing was made at a nearby airport with flaps retracted and landing gear partially extended. The airplane overran the departure threshold, coming to rest about 100 feet from the start of the runway. Examination of N372AC revealed white paint transfer markings and scrapes on the left wing deice boot, the outboard side of the left engine cowling was crushed inboard, the left wing-strut leading edge was torn open and bent, and the lower fuselage skin immediately forward of the landing gear wheel wells and stub wing was torn from left to right, consistent with a propeller strike.
Aftermath for N3735W
N3735W impacted terrain and was destroyed during a subsequent ground fire. The flight crew and a passenger were killed. The outboard three-quarters of the left wing separated from the main wreckage and was not fire damaged. The upper wing surface had linear scrapes diagonally across the skin. The left aileron from N3735W was found on the runway where N372AC had landed.
Official Findings
The probable cause of the accident was the failure of the other airplane's flight crew to maintain clearance while maneuvering during formation flight. Contributing to the accident was the decision of both flight crews to fly in formation.