N3159BAir Tractor AT-400 · 1982

On August 5, 2013, about 1015 central daylight time, an Air Tractor AT-400, N3159B, collided with a meteorological tower southwest of Balko, Oklahoma. The commercial pilot was fatally injured, and the airplane was destroyed. The airplane was registered to and operated by Terhune Flying Service, Inc., Perryton, Texas, under the provisions of 14 Code of Federal Regulations Part 137 as an aerial application flight. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight originated from a private airstrip near Perryton, Texas, about 1000.

The airplane was carrying 200 gallons of herbicides --- Roundup, Sterling Blue, and Traxion --- and about 100 gallons of fuel. The pilot was en route to spray a field about 2 miles northeast of the accident site. A witness, who was in a road grader about ½-mile north of the accident site, said the airplane was flying straight and level when it collided with the meteorological tower.

The pilot, age 34, held a commercial pilot certificate with airplane single and multiengine land ratings. He also held a second class airman medical certificate, dated January 24, 2013, with no restrictions or limitations. His last flight review was accomplished on March 8, 2012. His employer reported the pilot had accrued 1,750 total flight hours, of which 600 hours were in the Air Tractor AT-400.

N3159B, serial number 400-0462, a model AT-400, was manufactured by Air Tractor, Inc., of Wichita Falls, Texas, in 1982. It was powered by a Pratt & Whitney PT6A-15AG turboprop, serial number PCE-PD0130, rated at 680 shaft horsepower, driving a Hartzell HC-B3TN-3D/T10282N 4-bladed propeller.

A Federal Aviation Administration (FAA) inspector, who examined the maintenance records, reported the last annual inspection was performed in April 2013, and the last 100-hour inspection was dated July 23, 2013.

At 1035, the following pertinent METAR (METeorological Aviation Routine) weather observation was recorded by the Perryton Ochiltree County Airport's Automated Weather Observing System (AWOS), located about 10 miles southeast of the accident site:

Wind, 240 degrees at 14 knots; visibility, 10 miles; sky condition, clear; temperature, 33 degrees Celsius (C.); dew point, 14 degrees C.; altimeter setting, 29.99 inches of mercury.

A survey of the accident site revealed that at 1015, the sun would have been located just to the right of the airplane's flight path.

N3159B, serial number 400-0462, a model AT-400, was manufactured by Air Tractor, Inc., of Wichita Falls, Texas, in 1982. It was powered by a Pratt & Whitney PT6A-15AG turboprop, serial number PCE-PD0130, rated at 680 shaft horsepower, driving a Hartzell HC-B3TN-3D/T10282N 4-bladed propeller.

A Federal Aviation Administration (FAA) inspector, who examined the maintenance records, reported the last annual inspection was performed in April 2013, and the last 100-hour inspection was dated July 23, 2013.

The wreckage was located in a field on the east side of County Road NS119, midway between County Roads EW330 and EW340.

The on-scene investigation revealed the airplane had struck the 197-foot-tall guy-wire braced meteorological (MET) tower about 35 feet from its top. The tower took wind measurements and the data was to be used to determine the feasibility of constructing a wind farm. The upper portion of the tower was painted orange and white. Orange balls were attached to the guy wires. Three sections of the tower lay on the ground near its base. Approximately 7 feet of the outboard right hand wing was located near the base of the tower. The leading edge of the wing bore orange paint transfer marks consistent with the orange paint on the tower. The right hand aileron was crushed approximately mid span. The airplane had impacted the ground in a nose down attitude and came to rest about 1,200 feet away on a magnetic heading of 015 degrees. Leading up to the wreckage was a 350-foot ground scar strewn with aircraft parts.

The main body of wreckage lay inverted. The hopper and firewall were separated from the fuselage. The center portion of the wing structure was located with the primary wreckage. The right wing was stripped of its nose ribs. The spar bore marks consistent with multiple wire strikes. The left wing flap and aileron were crumpled. The leading edge skins and ribs were crushed downward, and the wing outboard of the fuel tank was severely damaged. The flap actuator was in the fully retracted position.

The empennage remained attached to the aft fuselage. The damaged stabilizers and control surfaces remained in place. The leading edge of the vertical stabilizer was torn along the main spar rivet line. The rudder remained attached at all three hinge points. The elevator controls were found with all bolts and attach points properly installed. The elevator control system was intact and properly connected.

The engine was found near the tail of the wreckage with the engine mount still partially attached. The propeller hub and planetary gears were found approximately 115 feet away from the main wreckage. The reduction gearbox was adjacent to the engine. Most of accessories mounted to the aft end of the engine had separated from the engine and were located nearby.

The propeller was severely damaged. Pieces of the propeller blades were scattered throughout the main wreckage area, with several pieces found at the beginning of the ground scar. Many of the smaller pieces of propeller blades were deformed into an almost cylindrical shape around the spanwise axis of the blade. No parts of the propeller or engine were found near the MET tower.

The meteorological tower (MET) was still standing with 5 sets of guy wires still attached. There were three pieces of the upper most portion of the MET tower lying near the base of the tower with some guy wires still attached. The three pieces measured 13 feet, 8 inches; 7 feet, 3 inches, and 13 feet, 7 inches. Yellow paint transfer marks, consistent with the airplane's color, were found on two of the pieces. Meteorological instruments were still attached to one of the pieces.

In a telephone conversation and e-mail with an Apex Wind Energy spokesman in Charlottesville, Virginia, he stated the meteorological tower had been erected on July 13, 2012. Apex Wind Energy has contracts with several property owners in the immediate vicinity for tower installations. One of the property owners told him he had seen this airplane fly over the area many times in the past and on the day of the accident, the airplane was seen flying back and forth along the same route several times.

In Section 7-5-3 of FAA's Aeronautical Information Manual, pilots are warned about obstructions to flight. Specifically, many structures exist that could significantly affect the safety of flight when operating below 500 feet above ground level (AGL), and particularly below 200 feet AGL. At and below 200 feet AGL, there are numerous power lines, antenna towers, etc., that are not marked and lighted as obstructions and; therefore, may not be seen in time to avoid a collision.

In the past, the National Transportation Safety Board (NTSB) has investigated three similar accidents in which airplanes inadvertently collided with meteorological towers, fatally injuring four people. These structures are just under 200 feet agl and therefore do not require FAA notification. As a result, on May 15, 2013, NTSB issued Safety Recommendations A-13-016 thru -021 to FAA; the American Wind Energy Association; , the Departments of Interior, Agriculture, and Defense; the governors of 46 states and 4 territories, and the mayor of the District of Columbia.

The Hemisphere Satloc CPU (central processing unit) of the GPS guidance system was removed from the airplane and sent to NTSB's Vehicle Recorder Division for download. It had an internal hard drive that was configured to log GPS data. According to the National Transportation Safety Board's (NTSB) Vehicle Recorder Division's report, the airplane was in cruise flight about 150 feet agl (above ground level) when the recording ended.

According to the autopsy report, the pilot's death was attributed to multiple acute blunt force traumas. According to FAA's Civil Aerospace Medical Institute (CAMI) toxicology report, there was no evidence of ethanol or drugs in the liver.