Background
The flight originated from Jones (Riverside) Airport. The pilot had filed an IFR flight plan and the aircraft operated under instrument meteorological conditions (IMC).
Flight
After departure, the airplane climbed to its assigned altitude while on course. At one point, air traffic control (ATC) asked the pilot about the ride conditions, and the pilot responded that it was "smooth so far." Shortly thereafter, the aircraft began veering to the right of its assigned heading. ATC advised the pilot of the deviation, and the pilot acknowledged. A correction was initiated but not completed. The aircraft again veered right, entered a steep descent, and disappeared from radar. The pilot did not respond to further radio calls from ATC.
Accident
The aircraft crashed in a steep nose-down attitude while at a high rate of speed during a heavy rainstorm.
Post-Accident Examination
Examination of the wreckage revealed no evidence of preimpact mechanical failure or malfunction. Pathological and toxicological examinations of the pilot found no evidence of a human factors problem.