Robinson R44 N89LA

Summary

On 8 August 2020 at about 23:45 local time, a Robinson R44 registered N89LA, operated by Cedar Ridge Aviation, LLC, was involved in an accident near Logan, Iowa, United States. One person was on board and one was seriously injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

8 August 2020 at 23:45

Classification

Accident

Location

Logan, Iowa, United States

Coordinates

41.6317, -95.7935

Aircraft

Robinson R44

Registration

N89LA

Category

Helicopter

Year built

2005

Engines

1

Operator

Cedar Ridge Aviation, LLC

Operating rule

Part 137: Agricultural

Purpose of flight

Aerial Application

Phase of flight

Not recorded

Route

Logan → Unknown

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

CEN20LA330

1 person was seriously injured.

The failure of the lower actuator bearing support brackets, which resulted in the misalignment of the clutch actuator, a loss of belt tension on the main rotor drive system, and a subsequent forced landing.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

The commercial pilot had just completed several spray runs in the helicopter 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 initiated an autorotation to a cornfield, where the helicopter impacted an area of rising terrain and came to rest on its right side. The helicopter sustained substantial damage to the fuselage. 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 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. It is likely that, over time, the lower brackets supporting the lower actuator bearing became loose during flight operations and sheared the rivets, which allowed the actuator bearing to shift and led to a subsequent misalignment of the clutch actuator. The misalignment of the clutch actuator resulted in the loss of belt tension between the engine and the main rotor drive system. The pilot’s report of an unusual noise, the nose yaw, and an increase of engine rpm and a decrease in rotor rpm was consistent with a drive system failure. A review of the airframe maintenance logbooks showed no evidence of compliance with the helicopter manufacturer’s service bulletin RHC SB-94 and service letter RHC SL-61A. RHC SB-94 directs the inspection of the A185 brackets for evidence of fretting or looseness. RHC SL-61A directs actions to be performed whenever looseness of an A185 bracket is detected and whenever the upper or lower scroll was removed. The FAA does not require compliance with RHC SB-94 and RHC SL-61A for 14 CFR Part 91 and 14 CFR Part 137 operations.

Quoted verbatim from the NTSB record.