Impact Sequence
The aircraft struck marshy terrain while in a very shallow descent with wings level and at a relatively high speed, described as cruise speed. After impact, it cartwheeled and slid to a stop. Evidence indicated substantial engine power was being developed at the moment of impact.
Aircraft Configuration
The aircraft was equipped with extended range fuel tanks added to the wing tips, along with an in-cabin tank that provided an extra fuel capacity of 75 to 80 gallons. All tanks had apparently been filled prior to the accident. The aircraft was carrying contraband cargo. The autopilot's altitude hold function was engaged at the time.
Circumstances
The points of departure and intended landing are unknown, as is the time of the accident. No radar track of the aircraft was found, likely due to low altitude flight.
Probable Cause
The aircraft most probably descended due to a change in barometric pressure while the pilot was asleep or inattentive, leading to impact with the terrain.