Background
At the time of the accident, simultaneous flight operations were being conducted at the airport. Fixed-wing aircraft were flying left traffic for landing on runway 20, while military helicopters operated in right traffic to a midfield helipad located on the west (right) side of the runway.
Sequence of Events
According to the flight instructor (CFI) in the accident airplane, the student pilot had completed three touch-and-go landings and was proceeding around the pattern for a fourth landing. During the landing approach, as the airplane neared the runway, a helicopter "suddenly lifted to a hover." Multiple witness statements and security video showed that the 2,150-pound airplane followed another airplane that had landed on the runway and then passed abeam an 18,000-pound Army utility helicopter that was on final approach to the helipad. Shortly thereafter, the airplane banked sharply to the right and impacted the terrain.
Post-Accident Examination
A post-accident examination of the airplane by an FAA inspector revealed partial separation of the right wing and substantial damage to the fuselage. The CFI reported that there were no mechanical malfunctions or failures with the airplane that would have precluded normal operation.
Regulatory Guidance
According to the FAA's Aeronautical Information Manual, section 7-3-7, helicopters in a slow hover taxi or stationary hover generate downwash producing high-velocity outwash vortices up to approximately three times the diameter of the rotor. These vortices circulate outward, upward, around, and away from the main rotors. Pilots of small aircraft are advised to avoid operating within three rotor diameters of a helicopter in such conditions. Additionally, in forward flight, departing or landing helicopters produce strong trailing vortices similar to those of larger fixed-wing aircraft, and caution is advised when operating behind or crossing behind them.