On August 30, 1996, an Air Tractor AT-401 (registration N1558N) was involved in an aviation accident near Plains, TX. Investigators recorded the probable cause as: failure of the pilot to maintain control of the airplane, while maneuvering after a swath run, which subsequently resulted in a collision with the terrain. A factor relating to the accident was: the adverse wind condition (gusty wind and possible windshear). This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
While maneuvering for a swath run, a pilot experienced the left wing snapping over during right turns. On the third turn, extended with airspeed, full left stick and rudder prevented inversion. The aircraft descended rapidly, stalling just before impact. No mechanical anomalies found.
Incident Description
The pilot was conducting agricultural aerial application operations and had completed a swath run. While maneuvering to begin another swath run, the pilot encountered difficulties controlling the aircraft during a right turn. He described that the high (left) wing abruptly went over the top, comparable to a snap roll, and this had previously occurred during the two preceding right turns.
Pilot Report
On the third right turn, the pilot executed an extended turn while maintaining what he described as 'plenty' of airspeed. To prevent the left wing from completely rolling over, he applied full left forward stick and left rudder. Subsequently, the aircraft descended rapidly. The pilot stated that the aircraft stalled just before impact but clarified that it did not stall during the turn itself. He also reported that the wind was from the northeast at 5 knots gusting to 10 knots, and suggested that wind shear might have been encountered.
Examination Results
Post-incident examination of the airframe and engine revealed no mechanical anomalies. Control continuity was established to all flight control surfaces.