Weatherly Aviation Co Inc 620B N350WR accident near Ludlow, South Dakota

Probable cause

The pilot’s failure to maintain control of the airplane while maneuvering, which resulted in an inadvertent stall. Contributing to the accident was task- and/or work-related fatigue.

NTSB analysis

The pilot had been performing aerial applications; the airplane was found crashed in a field adjacent to the area where he was applying applicant. A map of the 891.72-acre application area showed that it was asymmetrical and that it included a series of diagonally adjoining rectangular fields bounded by fences and property and an irregularly shaped field bounded by a curved highway. The fields to be treated were located north, south, and east of the accident site. According to an aerial application pilot familiar with the work site, if the accident pilot were following a north-south application path, it would have been appropriate for the airplane to fly over the accident area in straight-and-level flight without spraying any materials in that area. However, given the irregular shape of the application area, it is possible that the pilot may have been maneuvering the airplane for a different application path to another part of the field.

An examination of the airplane, the engine, and related systems revealed no anomalies that would have precluded normal operation. The damage to the airplane and ground scars were consistent with the airplane being at a high angle-of-attack, consistent with a stalled condition, at the time of impact.

According to the pilot's colleagues, he got up at 0700 the morning of the accident after sleeping about 7 to 8 hours and started flying at 0930. He flew all morning and took a 10- to 15-minute break for lunch about 1300. The pilot then continued to fly until the time of the accident. He had flown at least 9 hours when the accident occurred. The low-level aerial application flight operations would have required considerable concentration to ensure proper application to the target crop, obstacle avoidance, and precise control of the airplane while dispensing multiple loads of chemical throughout the day. Such operations can induce fatigue, particularly when they are conducted during the course of a long work day like the pilot had. Therefore, it is likely that the pilot would have been affected by task- and/or work-related fatigue when the accident took place.

Text from the NTSB. Open the NTSB docket for CEN13FA324 for the full record.