N4843JAir Tractor AT-402B · 2008

On July 17, 2012, about 1630 central daylight time, an Air Tractor AT-402B, N4843J, impacted terrain during an aerial application flight near Britt, Iowa. The pilot sustained fatal injuries. The airplane was substantially damaged by impact forces and a postimpact fire. The airplane was registered to and operated by Friesenborg & Larson Custom Spraying under the provisions of 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed for the flight, which was not operating on a flight plan. The flight departed the Forest City Municipal Airport (FXY) at an unconfirmed time.

A witness reported observing the accident airplane spraying corn about 2 miles south of his farm yard. He noted that the airplane was turning within 1/2 mile of his position during the application runs. He heard the engine start to “sputter” and looked south to see if he could see the airplane. At that moment, he observed a “large ball of fire go up” and subsequently called 911 to report the accident. He added that there were two separate “large” explosions; the first was about 1 minute and the second was about 3 minutes after the accident. These were followed by 2 or 3 “small” explosions about 15 minutes later.

The airplane came to rest inverted in a corn field located about 3 miles northeast of Britt, Iowa.

The pilot held a commercial pilot certificate with single-engine land airplane and instrument airplane ratings. He held a flight instructor certificate with a single-engine airplane rating, issued on March 10, 2012.

The pilot was issued a second class airman medical certificate on April 5, 2012, with a restriction for corrective lenses. On the application for that medical certificate, he indicated a total flight time of 2,890 hours, with 30 hours within the previous 6 months.

The accident airplane was a 2008 Air Tractor AT-402B, serial number 402B-1207. The airplane was a single-engine airplane equipped for agricultural application operations. It was powered by a Pratt & Whitney Canada PT6A-15AG turbine engine, serial number PCE-PD0102, and a Hartzell three blade, adjustable pitch propeller. The airplane was issued a restricted category airworthiness certificate on June 8, 2008.

A review of maintenance records revealed that the most recent annual inspection was completed on June 1, 2012, at 734.0 hours total airframe time. The records contained no subsequent maintenance entries.

The accident airplane was painted yellow, with blue trim. A similar paint scheme is displayed on AT-402 airplanes depicted on the airframe manufacturer’s website.

The Mason City Municipal Airport (MCW) Automated Surface Observing System (ASOS) was located about 19 miles east of the accident site. At 1553, the MCW ASOS recorded conditions as: wind from 250 degrees at 12 knots, gusting to 17 knots; 10 miles visibility, clear skies, temperature 36 degrees Celsius, dew point 18 degrees Celsius, and altimeter 29.84 inches of mercury.

At 1653, the MCW ASOS recorded conditions as: wind from 220 degrees at 9 knots; 10 miles visibility, clear skies, temperature 36 degrees Celsius, dew point 18 degrees Celsius, and altimeter 29.84 inches of mercury.

The airplane came to rest inverted in a corn field about 3 miles northeast of Britt, Iowa. A set of power transmission lines bordered the east edge of the field. About 1/2 mile from the north edge of the field, the lines turned 90 degrees and proceeded west across the corn field. The power transmission lines consisted of three transmission lines and two static lines, supported by a double set of poles and crossbeam configuration. The transmission lines were estimated to be about 60 feet high. At the point the transmission lines turned 90 degrees, the individual lines were mounted vertically on a single pole. The lower line had been severed at this point, and showed yellow marks on the line consistent with paint transfer. There was also an area of burned vegetation along the roadway ditch adjacent to the support pole.

A second set of power distribution lines, about 20 feet high, were located along the east side of the north-south road bordering the east edge of the field. These lines consisted of two distribution cables supported by a single pole configuration.

A depression in the corn was located about 300 feet west of the severed power line. The intact corn was about 9 feet high, with up to 2 feet having been cut from the corn in the depressed area. The transmission line support about 260 feet west of the corn depression was damaged. The north vertical support pole and the crossbeam were broken, and the north transmission line was down. Yellow marks consistent with paint transfer were observed on the power line and insulators. Fragments attributed to the left wing were located in the vicinity, which included wing skin and rib fragments, portions of the outboard main spar, and the wing tip.

The airplane came to rest about 600 feet west-northwest of the broken transmission line support pole. The airplane was inverted and oriented on an approximate 022-degree magnetic bearing. The postimpact fire consumed a majority of the fuselage skin to the empennage. The fuselage frame was deformed consistent with impact forces and thermal effects.

The left wing was fragmented. Some fragments, located up to 50 feet from the main wreckage, exhibited crushing damage. The main spar remained attached to the fuselage and was deformed aft about 30 degrees. The rear spar had separated from the fuselage. The inboard portion of the left wing flap remained with the wing; however, the outboard portion of the flap appeared to have been consumed by the postimpact fire. The left aileron had separated from the wing. Components of the left aileron were not identified with the main wreckage; however, portions of the left wing were located near the broken transmission line support pole.

The right wing had separated from the fuselage; although, the wing itself remained intact with the exception of damage due to impact forces. The fracture surfaces of the wing attachment bolts appeared consistent with overstress failure. The right flap and aileron remained attached to the wing. Portions of the entire right wing structure sustained postimpact thermal damage.

The vertical and horizontal stabilizers remained attached to the fuselage. The right stabilizer exhibited leading edge crushing damage near mid-span. A section of the right elevator, outboard of the trim tab, was separated, which was recovered from the debris path. The rudder remained attached to the vertical stabilizer.

Elevator and rudder control continuity were confirmed from the flight control surfaces to the cockpit controls. The cockpit control stick support structure and the rudder pedals were consumed by the postimpact fire. Damage to the aileron control system appeared consistent with impact forces and the postimpact fire. The wing flap actuator was positioned consistent with a flaps-up configuration at the time of the examination.

The engine remained in position relative to the fuselage. The engine and engine mount exhibited damage consistent with impact forces. Engine control continuity was confirmed. The propeller assembly remained secured to the engine. One propeller blade exhibited S-bending, with a portion of the blade tip being separated. The second blade was bent forward over the length of the blade, with a portion of the blade tip being separated. The third blade was separated, with the inboard 8-inch portion of the blade remaining attached to the hub. The remaining portion of this blade was recovered near the main wreckage. The blade was curled aft near the tip and exhibited trailing edge gouges. The fracture surfaces on all three blades appeared consistent with overstress separations.

The pilot was critically injured in the accident. He was subsequently transported to a local hospital and died about 8 hours later. An autopsy of the pilot was conducted on July 18, 2012, at the University of Iowa Hospitals and Clinics in Iowa City, Iowa. The pilot’s death was attributed to injuries initially sustained in the accident.

The FAA Civil Aerospace Medical Institute toxicology report noted:

Etomidate detected in Liver;

Etomidate detected in Blood (Heart);

Midazolam detected in Liver;

Midazolam not detected in Blood (Heart);

No carbon monoxide detected in Blood (Heart);

No ethanol detected in Vitreous.

The medications noted are commonly administered in an emergency medical setting.

A review of call records related to the pilot’s cellphone number revealed that two calls occurred near the time of the accident. An outbound call was initiated at 1614, which was 9 minutes, 29 seconds in duration. An inbound call was received at 1625, which was 2 minutes, 7 seconds in duration. All subsequent calls to the pilot’s cellphone number went to voicemail.