Incident Overview
On approach to runway 36R, an airplane descended to an altitude of approximately 10 to 15 feet above the runway surface. A witness observed the airplane yaw to the left, then roll left, subsequently colliding with the ground in an inverted position.
Investigation Findings
Examination of the airframe, engines, and propellers revealed no evidence of mechanical malfunction. Both propellers displayed twisted blades and chordwise gouges; each propeller low pitch stop exhibited an impression mark.
Radar and Wake Turbulence Analysis
Radar data for the accident airplane's approach to runway 36R indicated that an Embraer ERJ 145 had landed on runway 36C approximately 120 seconds before the accident airplane attempted to land on runway 36R. The last recorded horizontal separation between the two airplanes was 3.53 nautical miles.
A study incorporating radar data, wind data, and wake vortex characteristics developed ground track and wake vortex profiles for both airplanes. According to the study, "the wake vortex of the ... [Embraer ERJ 145] ... could have migrated toward the ... [Beech 58P's] flight path." The study also noted that Federal Aviation Administration (FAA) guidance "suggests that a separation of 120 sec[onds] is sufficient for the wake to dissipate or move away from the runway. Furthermore, wake dissipation is enhanced in ground effect."
Separation Standards
According to FAA guidelines, for wake turbulence separation purposes, runways 36R and 36C are considered as a single runway due to their proximity. The separation minima for a "small" aircraft (Beech 58P) following a "large" aircraft (Embraer ERJ 145) is four miles.