History of Flight
On July 17, 2012, at about 1630 central daylight time, an Air Tractor AT-402B, registration N4843J, impacted terrain while conducting an aerial application flight near Britt, Iowa. The airplane was operated by Friesenborg & Larson Custom Spraying under 14 Code of Federal Regulations Part 137. Visual meteorological conditions prevailed, and the flight was not operating on a flight plan. The departure from Forest City Municipal Airport occurred at an unconfirmed time.
A witness reported observing the airplane spraying corn approximately 2 miles south of his farm. During the application runs, the airplane was turning within half a mile of his position. He heard the engine sputter and then saw a large fireball. He called 911 and reported two separate large explosions, followed by smaller ones. The airplane came to rest inverted in a corn field about 3 miles northeast of Britt.
Personnel Information
The pilot held a commercial pilot certificate with single-engine land and instrument ratings, as well as a flight instructor certificate issued on March 10, 2012. His most recent second-class medical certificate, issued April 5, 2012, required corrective lenses. On that application, he reported 2,890 total flight hours, with 30 hours in the previous 6 months.
Aircraft Information
The accident airplane was a 2008 Air Tractor AT-402B, serial number 402B-1207, powered by a Pratt & Whitney Canada PT6A-15AG turbine engine and a Hartzell three-blade adjustable-pitch propeller. It was issued a restricted category airworthiness certificate on June 8, 2008. The most recent annual inspection was completed on June 1, 2012, at 734.0 hours total airframe time, with no subsequent maintenance entries. The airplane was painted yellow with blue trim.
Meteorological Information
Weather conditions recorded at the Mason City Municipal Airport ASOS, about 19 miles east of the accident site, included at 1553: wind from 250 degrees at 12 knots gusting to 17, 10 miles visibility, clear skies, temperature 36°C, dew point 18°C, altimeter 29.84 inches of mercury. At 1653: wind from 220 degrees at 9 knots, with other conditions similar.
Wreckage and Impact Information
The airplane came to rest inverted in a corn field. A set of power transmission lines bordered the east edge of the field, with lines about 60 feet high. At a point where the lines turned 90 degrees, the lower line was severed and showed yellow paint transfer. Burned vegetation was noted near the support pole. A second set of 20-foot power distribution lines ran along the east side of the north-south road.
A depression in the corn was located about 300 feet west of the severed line, where intact corn was about 9 feet high and up to 2 feet cut in the depressed area. The transmission line support about 260 feet west of the depression was damaged, with yellow marks on the line and insulators. Fragments of the left wing were found in that area.
The main wreckage was about 600 feet west-northwest of the broken support, inverted on an approximate 022-degree magnetic heading. A postimpact fire consumed most of the fuselage skin to the empennage. The left wing was fragmented, with the main spar attached and deformed aft about 30 degrees; the rear spar separated. The right wing separated from the fuselage but remained mostly intact, with attachment bolts showing overstress failure. The tail surfaces remained attached; the right stabilizer had leading edge crushing and a section of the right elevator separated. Control continuity was confirmed for elevator and rudder; the aileron system was damaged by impact and fire. The wing flap actuator indicated a flaps-up configuration.
The engine remained in position, with control continuity established. The propeller assembly was secured; one blade exhibited S-bending with a separated tip, another bent forward with tip separation, and a third separated at the inboard 8 inches, recovered near the wreckage. Fracture surfaces were consistent with overstress.
Medical and Pathological Information
The pilot sustained fatal injuries in the accident. He was transported to a local hospital and died approximately 8 hours later. An autopsy on July 18, 2012, attributed death to injuries from the accident. The FAA toxicology report detected etomidate in liver and blood, and midazolam in liver, but not in blood; no carbon monoxide or ethanol was found. These medications are commonly administered in emergency medical settings.
Additional Information
Cellphone records showed an outbound call at 1614 lasting 9 minutes 29 seconds, and an inbound call at 1625 lasting 2 minutes 7 seconds. Subsequent calls went to voicemail.