On August 28, 1998, an Air Tractor AT-401 (registration N4543F) was involved in an aviation accident near N. Ottawa Twp., MN. Investigators recorded the probable cause as: A loss of engine power due to a worn piston ring. A related factor was the owner exceeded the manufacturer's recommended engine overhaul. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
An aerial applicator lost partial engine power shortly after takeoff. The pilot jettisoned the chemical load and attempted a forced landing, but the right wingtip and landing gear struck the ground, causing the aircraft to cartwheel and come to rest inverted.
Accident
Approximately five minutes after an aerial applicator flight departed, the pilot reported that the engine experienced a partial power loss. The pilot stated that the aircraft 'did not want to climb and began to settle down.' He jettisoned the chemical load and maneuvered for a landing. During the landing attempt, the right wingtip and landing gear struck the ground. The aircraft cartwheeled and rolled over the ground before coming to rest inverted.
Investigation
On-scene examination revealed that one engine cylinder had no compression. Further inspection showed the piston rings were badly worn and the cylinder lacked taper. At the time of the accident, the engine had been operated approximately 70 hours beyond the manufacturer's recommended overhaul time. The aircraft had received an annual inspection about four months before the accident, and the engine logbook documented that all compression readings were within the manufacturer's recommended range.
Probable Cause
The investigation did not explicitly state a probable cause.