What happened
The pilot was conducting an instrument approach when reaching decision altitude at the middle marker. At this point, the runway environment was in sight, allowing for a visual transition. As the airplane crossed over the runway threshold, the pilot began the flare maneuver to initiate landing.
Immediately following the flare initiation, the aircraft entered a dense bank of fog that had not been anticipated or visible earlier in the descent. The pilot recognized the deteriorating visibility and immediately initiated a missed approach procedure. Despite the go-around attempt, the airplane touched down on the runway surface. Shortly after touchdown, the aircraft swerved off the paved surface and descended down an embankment adjacent to the runway.
The investigation
The investigation focused on the sequence of events surrounding the missed approach and the subsequent departure from the runway. Examination of the flight path indicated that the transition from visual reference to instrument flight was compromised by sudden local weather conditions. The structural damage sustained was consistent with a high-energy impact with terrain after leaving the runway environment.
Findings
The primary factor in this incident was the unexpected loss of visibility during the critical phase of landing. The pilot had met the minimums for the approach and had visual contact, but the rapid onset of fog obscured the runway environment just as the flare began. This sudden degradation of weather conditions prevented the pilot from completing a safe landing or executing a successful go-around with adequate terrain clearance.