NTSB Factual Report

On February 5, 2015, about 1510 central standard time, an Air Tractor AT-602, airplane, N602PB, impacted terrain shortly after departing the Slaton Municipal Airport (F49), Slaton, Texas. The commercial rated pilot was not injured and the airplane was substantially damaged. The airplane was registered to Neal Aircraft, Inc., Slaton, Texas and operated by Frontier Ag Inc., Oakley, Kansas, under the provisions of the 14 Code of Federal Regulations Part 91 as a cross country flight. Visual meteorological conditions prevailed at the time of the accident.

The pilot reported that prior to departure the airplane was filled with fuel. After engine start, he taxied to runway 18, and conducted an engine run-up with no anomalies noted. The initial takeoff appeared normal; however, about half way down the runway, he noticed a "lack of airspeed" and the engine monitor was flashing "several red lights". About this time, the airplane became airborne. The pilot added that he was able to climb to about 150 feet, before he noticed an additional power loss. He kept adding throttle and even with full power selected, the airplane lost altitude. The pilot was able to land in a field south of the airport; however, the landing gear dug into the soft dirt and the airplane nosed over, coming to rest inverted. The pilot added that the engine never developed full power, even after adding full throttle.

Examination of the airplane by the responding Federal Aviation Administration (FAA) inspector revealed the vertical stabilizer and wings were substantially damaged, and the engine was fractured at the propeller reduction gearbox. The airplane was equipped with an AmSafe airbag system; however, the airbags did not deploy during the accident.

The airplane was recovered to a nearby hangar for further examination. The engine was removed from the airframe and sent to Pratt & Whitney, Service Investigation Center, in Bridgeport, West Virginia, for further examination. The associated engine pressure line (Py) line was retained for examination, at Air Tractor's facility in Olney, Texas. The Electronics International, MVP-50 Engine Monitor, which was recently installed, was downloaded for review. Pratt & Whitney, along with Air Tractor under the supervision of the FAA conducted an engine examination on April 1, 2015. The engine a PT6A-65AG had accumulated 273 hours, per the engine maintenance record, dated January 30, 2015. The gas generator module was deformed and had contact signatures with internal components. The compressor and power turbine rotational signatures were indicative of rotation at impact; however, the level of engine power produced could not be determined. Examination and bench testing of the fuel control unit, fuel pump and flow divider valve, did not reveal any defects. Additionally, a visual examination and disassembly of the propeller governor did not reveal any anomalies.

The flexible air signal line (Py) is a reference pressure line runs from the propeller governor on the forward end of the engine to the Fuel Control Unit (FCU). The line pressure is used by the FCU to regulate fuel flow to the engine. Complete loss of this pressure results in the FCU reducing fuel flow. The flexible line was installed by Air Tractor during aircraft production under Supplemental Type Certificate (STC) #SE8652SW and is a replacement for the Pratt & Whitney rigid Py line. Examination of the Py line was conducted by Air Tractor, on September 9, 2015, under the supervision of the NTSB. The line was pressurized using standard shop air pressure (approximately 125 psi) and was submerged in water to check for leaks. No air leakage was noted during the test.

The engine examination did not reveal any pre-impact anomalies that would have precluded normal engine operation.

A review of the aircraft maintenance records revealed that the Electronics International Inc., MVP-50T, engine monitor's installation, was completed on January 30, 2015. The log entry noted that the monitor was installed under STC # SA02135SE. The entry noted that ground runs and leak checks were completed and no defects noted. The STC installation of the monitor included instructions, an initial setup, and installation checklists. A completed copy of either the setup or installation checklists, were not found in the records. The accident flight was the airplane's first flight after installation of the engine monitor. Review of the monitor's setup revealed the unit's clock was set to one hour earlier then local time, and the fuel flow calibration factor, was off by a factor of 10, meaning the monitor would indicate fuel flow ten times the actual fuel flow.

Each time electrical power is applied to the engine monitor a file is created. Download of the data revealed 32 data files, with dates ranging from January 19, 2015 to February 5, 2015. Only two of the files contained engine starts; February 2, 2015 and the accident flight on February, 5, 2015. The data for the February 2nd file, logged a maximum reading of 950 rpm for the engine propeller.

Reviewing the February 5 data obtained from the engine monitor, showed propeller rpm increasing at 14:10:27 (engine monitor time), consistent with start of the takeoff roll. The rpm reading went to zero (propeller stops) at 14:11:41; about a one minute and fourteen second flight.

During the takeoff run, the propeller rpm reached 1,730 rpm at an engine torque of 1,304 ft-lbs. About 21 seconds after power was applied for the takeoff, the torque reached 1,492 ft-lbs, and was the maximum seen for the entire flight. The torque then dropped to about 1,200 ft-lbs and remained there for about 20 seconds before further reduction was noted. The propeller rpm remained at 1,730 rpm for about 32 seconds after maximum torque was reached, then dropped below 1,700 rpm, with a torque reading of 736 ft-lbs, The torque then dropped into the 500 ft-lbs range, before a slight increase was noted about 10 seconds before the crash; the rise was followed by a decrease in the torque.

The engine's maximum torque was 3,245 ft lbs, with a propeller maximum limit of 1,700 rpm. The maximum rpm would have been set on the propeller governor at Air Tractor, using the standard airplane's analog instruments.

The engine monitor's engine operating range for the propeller was correctly set at 1,700 rpm. Rpm readings above the maximum of 1,700 would have been indicated to the pilot by red warning light.

The pilot held a commercial pilot certificate and ratings for single engine-land and instrument- airplane. The pilot reported that he had 561 total flight hours and 3 hours in the accident airplane make and model.

NTSB Probable Cause

Maintenance personnel’s improper installation of the engine data monitor (EDM), which was not in accordance with the supplemental type certificate instructions and resulted in engine warning indications and the pilot’s subsequent reaction to the warning indications due to his lack of experience with the EDM and airplane.