Accident Details
On September 8, 2008, at approximately 1147 mountain daylight time, a single-engine Diamond DA-20-C-1 airplane, registration N939DA, sustained substantial damage upon impact with terrain near Pueblo Memorial Airport (PUB) in Pueblo, Colorado. The flight instructor and student pilot on board were seriously injured. The aircraft was owned by Doss Aviation Incorporated and operated under contract by the United States Air Force. The local instructional flight had departed from PUB under visual meteorological conditions, operating under 14 Code of Federal Regulations Part 91 as a public use flight.
Flight History
According to statements from the flight instructor and student pilot, while entering the traffic pattern for runway 8L using an overhead approach, the tower controller advised them to follow a C-130 and be cautious of wake turbulence. Following the flight instructor's directions, the student pilot turned and entered the downwind leg. The instructor observed the C-130 on a wider pattern and chose to extend the downwind leg, initiating a turn to final approximately 1 nautical mile past the runway threshold. Both pilots reported that engine and airspeed indications appeared normal. On final approach, the student pilot attempted to maintain a higher altitude, noting that the glide slope indicators showed two red and two white lights. At about half a mile from the runway threshold, the airplane encountered wake turbulence from the preceding C-130. The aircraft experienced an uncommanded pitch-up, rolled left, and began to descend. Full throttle and opposite flight controls were applied. Despite efforts by both pilots to regain level flight, the airplane continued descending until it struck the terrain.
Aircraft and Engine Examination
An examination of the airframe and engine was conducted by the NTSB with assistance from Diamond Aircraft and Teledyne Continental Motors. Flight control continuity was confirmed to the ailerons, elevators, and rudder. The flaps were found in the landing position. No anomalies were identified that would have precluded safe operation. Engine examination revealed valve train continuity, accessory gear continuity, compression, and suction. The fuel manifold contained traces of fuel, and the fuel screen was clear. Both magnetos produced spark at all terminals. The throttle was at approximately full throttle position, and the mixture control was near full rich. The fuel inlet screen and oil filter were free of debris. No issues were found that would have prevented normal engine power production.
Radar Data and Weather
Review of tower radar data showed that the accident airplane flew 56 to 62 seconds behind and within 1/4 to 1/2 nautical miles downwind of the preceding C-130's flight path. At 1153, the automated weather observation facility at PUB recorded winds from 120 degrees at 7 knots, visibility 10 miles, ceiling broken at 2,500 feet, overcast at 3,900 feet, temperature 54 degrees Fahrenheit, dew point 39 degrees Fahrenheit, and barometric pressure 30.30 inches of mercury. Federal Aviation Administration Advisory Circular 90-23F, Aircraft Wake Turbulence (February 20, 2002), notes that an aircraft's ability to counteract wake vortex-induced roll depends on wingspan and control responsiveness.