Accident
On August 8, 2020, about 1845 central daylight time, a Robinson Helicopter Company 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 Part 137 aerial application flight.
Pilot Actions
The pilot was assigned to spray a 380-acre cornfield. After completing several spray runs, while turning to line up for another run, the pilot 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.
Postaccident Examination
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.
Maintenance Findings
The Robinson 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. RHC SB-94, dated June 8, 2017, directs the inspection of the A185 brackets for evidence of fretting or looseness, noting that "loose brackets can allow lower bearing to misalign resulting in belt-tension actuator damage." RHC SL-61A, dated July 21, 2017, directs actions including installing a third middle rivet on each upper bracket when looseness is detected or when the scroll is removed. The RHC R44 Series Maintenance Manual requires a 100-hour inspection of the lower actuator bearing and brackets for signs of cracking, looseness, and wear. A review of the airframe maintenance logbooks showed no compliance with RHC SB-94 or RHC SL-61A. Compliance with these documents is not mandated by the Federal Aviation Administration for 14 CFR Part 91 and Part 137 operations.
Probable Cause
The source does not state a probable cause.