NTSB Factual Report

On August 9, 2017, about 0730 central daylight time, an Air Tractor AT-802A, N528MB, sustained substantial damage during a forced landing near Galesburg, Illinois. The commercial pilot was not injured. The airplane was registered to and operated by Lesco Aviation Inc. under the provisions of 14 Code of Federal Regulations Part 137 without a flight plan. Day visual meteorological conditions prevailed for the local aerial-application flight that departed at 0630 from Monmouth Municipal Airport (C66), Monmouth, Illinois.

The pilot reported that the accident occurred about an hour into his first aerial-application flight of the day. He stated that he felt a slight "thud or bump" that he initially believed was the airplane flying through its own propeller wash during a turn. The pilot stated that the engine gauges were indicating normal parameters as he continued to line-up for another spray pass; however, before his next spray pass the engine experienced a similar "thud" that the pilot identified as a compressor stall. The pilot entered a climb to gain safe altitude and maneuvered the airplane away from nearby homes. The pilot reported that the engine experienced several more compressor stalls and observed sparks departing the engine exhaust ducts before it experienced a total loss of power. The pilot stated that a forced landing was made in a nearby agricultural field, and that the airplane ground-looped upon landing in the dense crop. The landing gear collapsed and there was substantial damage to the outboard right wing and aileron.

The engine, a Pratt & Whitney PT6A-67AG, serial number PCE-RD0221, was retained for a teardown examination.