Ayres Corporation S2R N4004K accident near Stanwood, Michigan

Probable cause

The pilot’s failure to maintain terrain clearance during a low-level aerial application flight, which resulted in impact with terrain and a subsequent forced landing. Contributing to the accident was the location of the spray boom pressure gauge, which required the pilot to divert his attention away from the airplane’s flight path, and the operator’s decision to locate the spray boom pressure gauge outside of the cockpit.

NTSB analysis

The pilot was performing a low-level aerial application flight when he momentarily and partially turned his head and body to the left to view the spray boom pressure gauge, which was located on the left spray boom. Shortly after viewing the spray boom pressure gauge, the main landing gear impacted terrain. The pilot immediately pulled up, then performed a forced landing to a flat grass field. The pilot performed an emergency shutdown and egressed the airplane without further incident. The airplane sustained substantial damage to the fuselage and both wings.

The pilot reported that, in order to view the spray boom pressure gauge, he needed to look to the left and down, to about an 8 o’clock position. The pilot reported that it takes one to two seconds to view the readings accurately on the analog gauge due to the distance from the spray boom pressure gauge to the cockpit, which he estimated as about 8 ft. The pilot classified the location of the spray boom pressure gauge as a “bad design.”

All the operator’s airplanes were equipped with a pressure gauge mounted on the left side spray boom, which was the only source of spray boom pressure information. The operator reported that the pressure gauges are located on the spray booms because that location provided the most reliable reading. It is likely that the pilot, while his head and body were turned to the left to view the spray boom pressure gauge, inadvertently allowed the airplane to descend and impact terrain. If the spray boom pressure was located inside the cockpit on the instrument panel, the pilot would not need to look outside of the airplane, thus diverting his attention during low-level operations.

A similar accident occurred about 21 years prior, during which an airplane impacted wires after the pilot looked down to view the spray boom pressure gauge. Research indicated that some aerial application airplanes are equipped with spray boom pressure gauges inside the cockpit, or otherwise in the pilot’s forward line of sight.

Text from the NTSB. Open the NTSB docket for CEN24LA318 for the full record.