Accident Overview
On July 13, 2021, at 1654 central daylight time, an Air Tractor Inc. AT-401, registration N7315P, sustained substantial damage when it was involved in an accident near Carroll, Iowa. The pilot was not injured. The airplane was being operated under Title 14 Code of Federal Regulations Part 137 as an aerial application flight.
Sequence of Events
The pilot reported that he had completed half of the planned aerial application of a field when the engine lost power during a turn. The pilot executed a forced landing. The airplane impacted terrain, resulting in substantial damage to its wings.
Aircraft and Modifications
The airplane was modified by the installation of a Walter M601E-11 turbine engine through supplemental type certificate SA01281CH issued to Johnson Airspray Inc.
On-Scene Examination
An on-scene examination of the engine by a Federal Aviation Administration (FAA) principal maintenance inspector and representatives from GE Aviation revealed no mechanical anomalies that would have precluded normal operation. Subsequent removal and testing of the engine-driven fuel pump and fuel control unit found that both met test specifications.
During the on-scene examination, a crane was used to level the aircraft, ensuring the airplane header fuel tank was full. The main fuel line from the airplane fuel filters to the engine-driven fuel pump was disconnected at the fuel pump end and placed in a bucket to capture fuel. The electric-driven airframe inline boost pump was turned on, but there was no fuel flow from the main fuel line. The B-nut on the hose from the header tank to the selector valve was loosened at the selector valve end to confirm fuel in the header tank; fuel was noted to be present. After retightening, the output fuel line from the airframe boost pump was loosened, and a small amount of fuel dripped. The dripping could be started and stopped by opening and closing the airplane fuel selector valve. The airframe boost pump was again turned on; there was no steady flow output and no bypass of fuel. The airframe boost pump was removed for further testing and examination at its manufacturer.
Fuel Pump Examination
The airframe boost pump was a Weldon pump, part number 2003-B, serial number 130661, manufactured on August 6, 2007. The pump was sent to Weldon Pump for testing under the supervision of an FAA aviation safety inspector. During testing, the pump was placed on a test stand and power applied. The pump energized and turned, but there was no fuel output, and fuel leaked from the shaft seal. The pump bypass was checked with no restrictions; fuel was able to flow through the pump. Disassembly of the pump from its electric motor revealed that the motor’s slotted shaft was worn to the point that it would not engage with the pump’s rotor tang. Weldon Pump representatives stated that the company recommended a 10-year overhaul requirement for the pump, with no time-in-service requirement specified.
Logbook Records
An airplane logbook entry dated July 8, 2013, with an hour meter reading of 2,497.8 hours, stated: “R&R FUEL PUMP P/N 2003B WITH OH UNIT. OPS CHECK GOOD.” At the time of the accident, the hour meter indicated 5,136.7 hours.