What happened
While conducting a low-level herbicide application, the pilot was flying at approximately 10 feet and 120 kt. During the run, the pilot activated the spray system to disperse herbicide from the hopper. However, the aircraft subsequently experienced an inadvertent descent, leading to the aircraft touching the ground and colliding with an irrigation levee.
The investigation
Investigators analyzed Satloc flight data, which revealed that no spray flow was recorded during the accident run. This was a unique occurrence, as ten days of previous flight data showed no such variation. The investigation determined that a visual 'no flow' warning was likely displayed on the Satloc system immediately after the spray was activated.
While the pilot had approximately 40 seconds of flight time during the run to notice the message, the investigation focused on the impact of cockpit distractions. Although the pilot's primary focus was external, the Satloc screen was within the visual scan. The investigation found that focusing on the 'no flow' message likely diverted the pilot's attention away from the external environment. Because the aircraft was flying at such a low altitude, even a momentary diversion prevented the pilot from detecting the descent, leaving insufficient height to recover before the collision.
Investigators also examined why the 'no flow' warning occurred. Due to high ambient temperatures and the lack of vegetation in the field, it was impossible to confirm if herbicide had actually been dispersed. Furthermore, the damage sustained during the impact made it difficult to determine if a spray system fault existed prior to the accident.
Findings
- The pilot's attention was likely diverted by a visual 'no flow' warning on the Satloc system.
- This diversion led to an inadvertent descent of the aircraft.
- The no flow recording could not be definitively attributed to a system fault or a lack of actual dispersal due to insufficient post-accident evidence.