N4004K

On June 20, 2024, about 0706 eastern daylight time, an Ayres Corporation S2R-600 airplane, N4004K, sustained substantial damage when it was involved in an accident near Stanwood, Michigan. The commercial pilot was uninjured. The airplane was operated as a Title 14 Code of Federal Regulations (CFR) Part 137 aerial application flight.

The purpose of the flight was to apply agricultural fungicide to a potato field in a rural area. The airplane departed earlier in the morning from the operator’s facility at Lakeview Airport (13C), Lakeview, Michigan.

The airplane was flying to the west, about 10 ft above ground level, traveling about 130 mph. The pilot had completed applying the liquid chemical to the potatoes and momentarily and partially turned his head and body to the left to view the spray boom pressure gauge that was located outside of the cockpit. Shortly after viewing the spray boom pressure gauge, the main landing gear impacted terrain. The pilot immediately pulled up to gain altitude. The left main landing gear was pushed up into the left wing from the impact and fuel leaked from the left wing fuel tank. The pilot performed a forced landing to a flat grass field, during which the airplane came to rest upright on the nose and forward fuselage. The pilot performed an emergency shutdown and egressed from the airplane without further incident.

The airplane sustained substantial damage to the fuselage and both wings. The pilot reported there were no preimpact mechanical malfunctions or failures with the airframe or the engine that would have precluded normal operation.

The pilot, who was wearing a flight helmet with a visor, reported that he did not feel fatigued during the accident flight.

The pilot reported that, in order to view the spray boom pressure gauge located aft of the left flap (about mid flap) and mounted on the left spray boom, he needed to look to the left and down, to about an 8 o’clock position. The pilot reported that it took 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 was about 8 ft. The pilot added that he could partially turn and view the spray boom pressure gauge while utilizing the four-point restraint system. The airplane was equipped with an Electronics International MVP-50T engine monitor system; however, this system was not configured to show spray boom pressure. The pilot, who was also a mechanic, classified the location of the spray boom pressure gauge as a “bad design.”

All the operator’s airplanes, which include five Thrush S2R series airplanes, were equipped with a spray boom 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 were located on the spray booms because that location provided the most reliable reading.

The Federal Aviation Administration (FAA) Type Certificate for the airplane, A4SW, is currently held by Thrush Aircraft, LLC, Albany, Georgia. The restricted category airplane was originally certified to Civil Air Regulations, Part 8. A review of the FAA Type Certificate Data Sheet A4SW (revision 44) and the FAA Advisory Circular 137-1B, Certification Process for Agricultural Aircraft Operators (published on August 21, 2017), did not reveal any guidance listed about the location of the spray boom pressure gauge.

According to Thrush Aircraft, airplanes manufactured since 2012 are equipped with an Electronics International MVP-50T engine monitor system that is configured to show spray boom pressure. A review of the Thrush Aircraft digital publications directory (containing service bulletins and service letters) did not reveal any guidance listed about the location of the spray boom pressure gauge.

A review of the Thrush Aircraft Model S2R Illustrated Parts Catalog, applicable to the airframe serial number, showed the spray boom pressure gauge being located on the instrument panel in the cockpit. A review of the Thrush Aircraft spray boom pressure gauge installation drawing 80809-9 showed the spray boom pressure gauge as being located outside of the cockpit, just forward of the windshield, on the hopper, and in the pilot’s forward-looking line of sight.

The operator reported that, when the airplane was purchased, it was not equipped with a spray boom system, nor was a spray boom pressure gauge located in the cockpit. The operator installed and configured the current spray boom system from another aerial application airplane.

In 2003, an Ayres Corporation S2R-T660 airplane (serial number T660-102), which was manufactured in 2000, impacted transmission wires during a low-level spray run and was subsequently destroyed (NTSB accident number CHI03LA273). The pilot, who sustained minor injuries, reported that during the spray run, he "looked down to check pressure gauge on spray boom [and] when I looked up [the] wires were in my face."