Accident Sequence
The accident occurred when a twin-engine airplane, operating under FAR Part 135 as an on-demand passenger flight, crashed into a harvested cornfield about 2.5 miles northeast of the airport. The airplane was returning to the airport after reporting an oil leak in the right engine. Radar track data showed the aircraft flew over the airport at about 550 feet above ground level (agl) at 97 knots calibrated airspeed (CAS), continued south, then turned north. The last radar return was at 1,116 feet mean sea level (msl) (344 feet agl) heading north at 99 knots CAS. The impact site was 2.5 miles north of that point. The airplane was found in a steep nose-down attitude, landing gear down, flaps at 20 degrees, and neither propeller feathered.
Preflight and Departure
The flight had been scheduled for a 0900 departure but was not confirmed, so no pilot was initially assigned. The accident pilot arrived at the airport about 1005 and reportedly spent less than two minutes in the office before grabbing the status book, walking directly to the airplane, and boarding. A lineman had serviced both engines with oil at 0930 but failed to replace the dipstick in the right engine oil filler tube, leaving it on the right wing. Witnesses did not see the pilot perform a preflight. After taxiing about 5 feet, the pilot stopped, shut down both engines, and exited. A lineman reported that the pilot closed the right engine oil flap door, stating it had been left open. The pilot then restarted the engines and departed about 1008.
Witness Observations
A witness about 1/4 mile from the crash site reported seeing the airplane flying "really low" and noted the engine was not cutting out or sputtering. Another witness stated the airplane lifted over power lines then crossed a field about 50 to 80 feet off the ground. The airplane impacted the cornfield at a steep angle and traveled 45 feet before stopping.
Post-Accident Inspection
Examination of the engines and airframe revealed no preexisting anomalies that could be associated with a pre-impact condition. The absence of preflight allowed the pilot to remain unaware of the missing dipstick, leading to an oil leak. The subsequent in-flight decisions and low airspeed resulted in an inadvertent stall.
Probable Cause
The probable cause, as determined by the official investigation, was the pilot's failure to preflight the airplane, the pilot's improper in-flight decision not to land on the runway when he had the opportunity, and the inadvertent stall when the pilot allowed the airspeed to get too low. Contributing factors were the lineman's improper servicing (leaving the oil dipstick out) and the subsequent oil leak.