What happened
Prior to departure, a flight service station specialist in McAlester provided a preflight briefing to the pilot of a Cessna 421. The briefing included warnings regarding instrument meteorological conditions (IMC) along the intended route and advised that flying under visual flight rules (VFR) was not recommended. At the time, cloud tops were reported at 12,000 feet, with a freezing level at 1,600 feet. A subsequent pilot report indicated light mixed icing between 6,400 and 9,000 feet near Oklahoma City.
The aircraft departed Tulsa under VFR, after which radar services were ended. The aircraft's last known position showed it climbing westward to 9,800 feet. Shortly thereafter, radar tracking indicated the plane began to deviate in both altitude and heading, eventually descending through 3,200 feet. Witnesses on the ground observed the aircraft exiting low clouds in a flat spin before impacting the ground. There was no evidence of mechanical failure prior to the impact.
Findings
Investigation into the accident revealed several contributing factors. The aircraft was operating at a gross weight approximately 150 lbs above its permitted maximum limit. While the aircraft was equipped for IFR and icing conditions, the pilot's training records from 1995 indicated significant difficulty maintaining altitude and heading when operating under IMC.
Additionally, postmortem toxicology results identified the presence of several substances in the pilot's system, including metabolites of Valium and Imipramine, as well as Diphenhydramine. These specific medications are not FAA-approved for use during flight operations.