History of Flight
On August 5, 2013, at approximately 1015 central daylight time, an Air Tractor AT-400, registration N3159B, collided with a meteorological tower southwest of Balko, Oklahoma. The commercial pilot was fatally injured, and the airplane was destroyed. The aircraft was registered to and operated by Terhune Flying Service, Inc., of Perryton, Texas, under 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, located in a road grader about half a mile north of the accident site, reported that the airplane was flying straight and level when it struck the tower.
Personnel Information
The pilot, aged 34, held a commercial pilot certificate with airplane single-engine and multiengine land ratings. He also held a second-class airman medical certificate issued January 24, 2013, with no restrictions or limitations. His most recent flight review was completed on March 8, 2012. According to his employer, the pilot had accumulated 1,750 total flight hours, of which 600 hours were in the Air Tractor AT-400.
Aircraft Information
N3159B, serial number 400-0462, was a model AT-400 manufactured by Air Tractor, Inc., in 1982. It was powered by a Pratt & Whitney PT6A-15AG turboprop engine (serial number PCE-PD0130) rated at 680 shaft horsepower, driving a Hartzell HC-B3TN-3D/T10282N four-bladed propeller. A Federal Aviation Administration inspector reviewed the maintenance records and reported that the last annual inspection was performed in April 2013, and the last 100-hour inspection was dated July 23, 2013.
Meteorological Conditions
At 1035, the Perryton Ochiltree County Airport's Automated Weather Observing System, located about 10 miles southeast of the accident site, recorded the following conditions: wind from 240 degrees at 14 knots; visibility 10 miles; sky clear; temperature 33°C; dew point 14°C; altimeter setting 29.99 inches of mercury. A survey of the accident site indicated that at 1015, the sun would have been located just to the right of the airplane's flight path.
Wreckage and Impact
The wreckage was found in a field east of County Road NS119, between County Roads EW330 and EW340. The airplane had struck the 197-foot-tall guy-wire-braced meteorological tower about 35 feet from its top. The tower, used for wind measurements to evaluate potential wind farm construction, had its upper portion painted orange and white, with orange balls attached to the guy wires. Three sections of the tower lay on the ground near its base. Approximately 7 feet of the outboard right wing was located near the tower base; the leading edge bore orange paint transfer marks consistent with the tower's paint. The right aileron was crushed near mid-span. The airplane impacted the ground in a nose-down attitude and came to rest about 1,200 feet away on a magnetic heading of 015 degrees. A 350-foot ground scar strewn with aircraft parts led to the main wreckage, which lay inverted. The hopper and firewall had separated from the fuselage. The center portion of the wing structure was with the primary wreckage. The right wing had lost its nose ribs, and the spar showed multiple wire strike marks. The left wing flap and aileron were crumpled; leading edge skins and ribs were crushed downward, and the wing outboard of the fuel tank was severely damaged. The flap actuator was fully retracted. The empennage remained attached to the aft fuselage, with damaged stabilizers and control surfaces in place. The vertical stabilizer's leading edge was torn along the main spar rivet line. The rudder remained attached at all three hinge points. Elevator controls were properly installed and intact. The engine was found near the tail with the mount partially attached. The propeller hub and planetary gears were about 115 feet from the main wreckage; the reduction gearbox was adjacent to the engine. Most aft-mounted accessories had separated and were nearby. The propeller was severely damaged, with blade pieces scattered throughout the area; many smaller pieces were deformed into an almost cylindrical shape. No propeller or engine parts were found near the tower. The meteorological tower remained standing with five sets of guy wires attached. Three pieces of the upper tower, measuring 13 feet 8 inches, 7 feet 3 inches, and 13 feet 7 inches, lay near the base with some guy wires still attached. Yellow paint transfer marks, consistent with the airplane's color, were found on two of those pieces; meteorological instruments remained attached to one.
Additional Information
According to a spokesman for Apex Wind Energy, the meteorological tower was erected on July 13, 2012. The spokesman stated that Apex Wind Energy has contracts with property owners in the vicinity for tower installations. One property owner reported seeing the airplane fly over the area many times previously and, on the day of the accident, observed the airplane flying back and forth along the same route several times.
The FAA's Aeronautical Information Manual, Section 7-5-3, warns pilots about obstructions to flight, noting that many structures exist that could affect safety when operating below 500 feet above ground level, particularly below 200 feet AGL, where power lines, antenna towers, and similar unmarked and unlighted obstructions may not be seen in time to avoid collision.
The National Transportation Safety Board has previously investigated three similar accidents involving inadvertent collisions with meteorological towers, which resulted in fatal injuries to four people. These structures, just under 200 feet AGL, do not require FAA notification. On May 15, 2013, the NTSB issued Safety Recommendations A-13-016 through -021 to the FAA, the American Wind Energy Association, various government departments and agencies, and the mayor of the District of Columbia.
Flight Recorders
The Hemisphere Satloc CPU of the GPS guidance system was removed from the airplane and sent to the NTSB's Vehicle Recorder Division for download. Its internal hard drive was configured to log GPS data. According to the NTSB's Vehicle Recorder Division report, the airplane was in cruise flight about 150 feet above ground level when the recording ended.
Medical and Pathological Information
An autopsy attributed the pilot's death to multiple acute blunt force traumas. The FAA's Civil Aerospace Medical Institute toxicology report found no evidence of ethanol or drugs in the liver.