Event Description
Shortly after takeoff, the pilot reported having "a problem...an overboost situation" and indicated a desire to return for landing. Instrument meteorological conditions were present, and air traffic control cleared the pilot for an ILS runway 26 approach. A witness on the ground saw the airplane appear from the low overcast in a wings-level descent. The aircraft then pitched over to a near-vertical attitude and struck a shopping center sign.
Wreckage Examination
Post-accident examination of the propulsion system revealed the left turbocharger wastegate in the open (low boost) position and the right turbocharger wastegate in the closed (high boost) position. The right turbocharger butterfly valve was severely eroded, its retaining pin was missing, and the valve was free to rotate on the shaft. A hole had been burnt through the right engine's number 1 cylinder exhaust valve. Both propellers were found in the low pitch–high rpm range. Additionally, both engines and their turbochargers were original equipment and had not been overhauled in the 21 years since manufacture.
Toxicological Findings
A toxicology test performed on the pilot detected 0.564 micrograms per milliliter of sertraline, an antidepressant medication, in the blood. According to the investigation, sertraline was not approved for use while operating an aircraft.
Probable Cause
The probable cause of the accident, as determined by the investigation, was the pilot's failure to maintain aircraft control. Factors contributing to the accident were the instrument weather conditions and the excessive workload imposed on the solo pilot while attempting to manage an emergency situation during flight in instrument meteorological conditions.