On August 8, 2020, about 1845 central daylight time, a Robinson Helicopter Company (RHC) R44II helicopter, N89LA, sustained substantial damage when it was involved in an accident near Logan, Iowa. The pilot sustained serious injuries. The helicopter was operated as a Title 14 Code of Federal Regulations (CFR) Part 137 aerial application flight. The pilot was assigned to spray a 380-acre cornfield. The pilot had just completed several spray runs and was turning to line up for another run, when he heard the engine emit a "pop" noise. The helicopter yawed “violently,” the engine rpm increased, and the rotor rpm decreased which caused both the low rotor rpm horn and light to activate. The pilot lowered the collective, entered “pedal correction,” and slightly pitched the nose of the helicopter back without “bleeding much airspeed off.” The helicopter continued to glide forward and descended toward a corn field. The pilot initiated a gradual flare and as the helicopter began to settle, he increased the flare. The helicopter impacted an area of rising terrain and came to rest on its right side. The helicopter sustained substantial damage to the fuselage. The RHC R44 Series Pilot’s Operating Handbook states that a drive system failure may be indicated by an unusual noise or vibration, nose right or left yaw, or increasing engine rpm with decreasing rotor rpm. A postaccident examination of the airframe revealed that all four V-belts that drive the rotor system were displaced from their grooves. Small areas of damage were visible in one belt. The lower and upper belt tension actuator support bearing rotated smoothly. The lower bearing brackets (also known as A185 brackets) were separated from the scroll and the belt tension actuator had rotated out of position. The mating surface of the brackets and the scroll were polished smooth, and the edges of the brackets had dug into the scroll. The attaching rivets were sheared flush with the mating surface of the brackets. The rivet holes in the scroll were elongated in the direction of engine rotation. The bracket backing plates were not present. The belt tension actuator had fractured just below the upper gear housing. RHC SB-94, dated June 8, 2017, is addressed to R44 series owners, operators, and maintenance personnel. RHC SB-94 directs the inspection of the A185 brackets for evidence of fretting or looseness. According to the SB, “loose brackets can allow lower bearing to misalign resulting in belt-tension actuator damage.” The compliance procedure is to visually inspect the A185 brackets and attaching rivets for evidence of fretting or looseness, and on the lower A185 bracket, apply torque seal in a vertical stripe across both outboard rivets to the lower scroll to highlight movement for future inspections. RHC SL-61A, dated July 21, 2017, is addressed to R44 series owners, operators, and maintenance personnel. The RHC SL directs actions to be performed whenever looseness of an A185 bracket is detected and whenever the upper or lower scroll was removed. To comply with SL-61A, a third middle rivet is to be placed on each upper bracket. The RHC R44 Series Maintenance Manual, states that a 100-hour inspection is required of the lower actuator bearing, including inspection of the fiberglass scroll area at the bearing attachment brackets for signs of cracking, and the lower bearing brackets for signs of looseness and wear. A review of the airframe maintenance logbooks showed no compliance with RHC Service Bulletin (SB)-94 nor RHC Service Letter (SL)-61A. Compliance with RHC SB-94 and RHC SL-61A is not mandated by the Federal Aviation Administration for 14 CFR Part 91 and 14 CFR Part 137 operations.