What happened
During a local instructional flight, a multiengine airplane entered a flat spin that led to an in-flight collision with the terrain. A witness holding a private pilot certificate observed the aircraft at approximately 1,500 feet agl in a flat spin before it impacted a pasture "flat on its bottom," roughly 400 yards north of the observer. Another witness also reported that the airplane was in a flat spin and unable to recover.
The crew consisted of a private pilot with a multiengine rating in the left seat and a multiengine flight instructor in the right seat.
The investigation
Investigators examining the accident site found the landing gear actuator in the extended position and the flap actuators set to 10 degrees. An examination of the right propeller revealed that blade counterweight signature markings on the blade sockets indicated the propeller was in the feathered position at the time of impact. Additionally, three separate cracks were discovered in the right propeller unfeathering accumulator at the transition between the thin-walled hemisphere of the diaphragm and the circumferential stiffener.
Toxicological analysis of the private pilot revealed several substances in the blood and urine. Detected levels included 0.462 (ug/ml, ug/g) of Citalopram (Celexa), 0.114 (ug/ml, ug/g) of N-desmethylcitapram, 0.024 (ug/ml, ug/g) of di-N-desmethylcitalopram, and 17.406 (ug/ml, ug/g) of acetaminophen in the urine. The analysis also found 0.194 (ug/ml, ug/g) of Diphenhydramine (Benadryl). The level of diphenhydramine in the pilot's blood was consistent with the recent ingestion of several times a normal dose.
Findings
Post-accident testing indicated that the pilot was likely impaired by the effects of diphenhydramine, an antihistamine with sedative properties.