Incident Overview
A flight instructor was providing commercial instruction to a dual student, who held a private pilot certificate, in an airplane. The airplane was observed flying at low altitude near Fertile Airport.
Witness Accounts
One witness reported seeing the airplane ascend from the airport and turn south. The witness stated that the airplane initiated a steeply banked left turn just above the treeline. The witness momentarily looked away and, upon turning back, the airplane was no longer visible. Another witness, located one mile east of the accident location, reported seeing the airplane perform a left, steeply banked turn before descending. This witness described the airplane as being low to the ground, comparable to the altitude of a spray plane turning after a pass over a field.
Wreckage Examination
Examination of the wreckage revealed a 3-inch-long crack in the number 5 engine cylinder exhaust pipe. The crack circumscribed the pipe approximately 1/4 inch to 1 inch below the flange where the pipe joined the cylinder. No other anomalies with the airplane were found.
Toxicology Results
State Medical Examiner's Laboratory tests on the dual student pilot showed a blood carbon monoxide level of 1.3 percent. Federal Aviation Administration (FAA) toxicology testing on the dual student pilot reported negative results for all tests conducted. According to FAA protocols, carbon monoxide is not reported as positive until it reaches a level of 10 percent. No carboxyhemoglobin tests were performed on the instructor pilot due to blood contamination.