Accident Overview
At 1350 CST, a McAlester Flight Service Station specialist provided a preflight briefing to a Cessna 421 pilot concerning instrument meteorological conditions (IMC) along the intended route and advised that VFR flight was not recommended. Cloud tops were reported at 12,000 feet, and the freezing level was at 1,600 feet. A pilot report (PIREP) at 1416 CST indicated light mixed icing from 6,400 to 9,000 feet near Oklahoma City.
Flight and Radar Data
The pilot departed Tulsa at 1424 CST under visual flight rules (VFR). Radar service was subsequently terminated, and no further communication was received from the airplane. Radar data showed the aircraft climbing westward, reaching 9,800 feet at 1440 CST. Over the next 88 seconds, heading and altitude deviations occurred until the aircraft descended through 3,200 feet.
Witness Accounts and Crash
Ground witnesses observed the airplane descending out of low clouds in a "flat spin" before crashing. No preimpact mechanical failure was found.
Aircraft and Pilot Information
The airplane's gross weight was approximately 150 pounds over its maximum limit. The aircraft was equipped for flight in icing and IFR conditions. In November 1995, the pilot completed 10 hours of Cessna 421 simulator training. The instructor noted in training records that the pilot met minimum standards for VFR, but "under IMC conditions," he "could not maintain altitude within 1,300 feet or heading within 40 degrees."
Post-Accident Toxicology
Postmortem toxicology tests detected Nordiazepam (a metabolite of Valium) at 0.079 mcg/ml in kidney fluid, Desipramine (a metabolite of Imipramine, an antidepressant) at 0.044 mcg/ml in spleen fluid, and Diphenhydramine (Benadryl) at 0.733 mcg/ml in spleen fluid and 0.353 mcg/ml in lung fluid. These medications are not approved by the FAA for use while flying.
Probable Cause
The National Transportation Safety Board determined the probable cause was the pilot's continued VFR flight into IMC and his failure to maintain control of the airplane after encountering adverse weather conditions, resulting in a stall/spin. Contributing factors were pilot impairment due to a medication not approved by the FAA for use while flying, the adverse weather conditions, and the pilot's lack of instrument proficiency in the Cessna 421 airplane.