What happened
On September 8, 2008, a Diamond DA-2-C-1, registration N939DA, was conducting a local instructional flight departing from Pueblo Memorial Airport (PUB) in Colorado. The flight was operating under 14 CFR Part 91 in visual meteorological conditions.
While entering the overhead pattern for runway 8L, the tower controller instructed the crew to follow a C-130 and warned them to be cautious of wake turbulence. Following instructions from the flight instructor, the student pilot entered the downwind leg. The instructor elected to lengthen the downwind leg, turning to final approximately 1 nautical mile past the runway threshold. Both the instructor and student pilot reported that engine and airspeed parameters were normal.
As the airplane leveled on final approach, the student pilot attempted to maintain altitude but noted the glide slope indicators were at "2 red/2 white." Approximately 0.5 miles from the runway threshold, the aircraft encountered wake turbulence from the preceding C-130. This caused an uncommanded pitch up and a left roll, followed by a descent. Despite the crew applying full throttle and opposite flight controls, the airplane continued its descent until it collided with terrain. The accident resulted in 2 serious injuries and no fatalities.
The investigation
NTSB investigators, with assistance from Diamond Aircraft and Teledyne Continental Motors, examined the airframe and engine. The investigation confirmed flight control continuity for the ailerons, elevators, and rudder, and found the flaps were in the landing position. No mechanical anomalies were found that would have prevented safe operation.
Engine inspections established continuity of the valve train, accessory gear, compression, and suction. The fuel manifold contained traces of fuel, the fuel screen and oil filter were clear of debris, and both magnetos produced spark. The throttle was found near the full throttle position and the mixture was near full rich.
Radar data from the tower showed the aircraft was flying 56 to 62 seconds behind and within 0.25 to 0.5 nautical miles downwind of the C-130's flight path.