Pilot Debrief

Robinson R44 near San Antonio, TX — 2019-12-14

Final reportERA20LA054
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Date
2019-12-14
Location
San Antonio, TX, USA
Airport
SSF
Aircraft
Robinson R44
Registration
N440AH
Category
Helicopter
Highest injury
Minor
Fatalities
0
Phase of flight
Initial climb

Probable cause

Maintenance personnel’s failure to complete all necessary steps of a service bulletin and subsequent failure to identify the loose lower actuator bearing support bracket during inspections, which resulted in the misalignment of the clutch actuator, resulted in a loss of belt tension on the main rotor drive system, and the subsequent forced landing.

NTSB narrative

After departure, the flight was uneventful as the helicopter climbed to 300 ft above ground level (agl) before turning toward a sightseeing area. As it climbed through about 650 ft agl, the pilot heard a single faint “bang” almost immediately followed by a very loud “bang.” Sound from the engine increased, and the tone changed significantly. The pilot saw the helicopter’s nose begin a yaw to the left and felt the helicopter begin to descend. He immediately entered an autorotation and began a quick briefing to the passengers encouraging them to remain calm. During the descent, the helicopter struck powerlines and came to rest on the left side, resulting in substantial damage. Postaccident examination of the upper and lower belt tension actuator support bearing brackets revealed they were separated from the fan scroll. In addition, the rivet holes in the fiberglass scroll for the upper two brackets were elongated, and the associated rivets were sheared. It is likely that the upper brackets supporting the lower actuator bearing became loose and sheared the rivets, which allowed the actuator bearing to shift, the actuator screw tube to bend, 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 main rotor drive system. Service Bulletin (SB) 94, in accordance with Service Letter 61, advised owners, operators, and maintenance personnel to inspect the brackets for looseness, to install additional rivets to the lower brackets, and to apply torque seal to the lower bracket to facilitate future inspections. The helicopter’s logbook indicated that the SB was accomplished on November 24, 2017. The extra rivets had not been added to the accident helicopter per the SB. The helicopter had been inspected in accordance with the manufacturer’s 100-hr and annual inspection programs within 3 and 10 months, respectively, of the accident. The 100 hr inspection guidance specifically indicated an examination of the lower brackets for evidence of looseness or fretting and had been completed only 59 flight hrs prior to the accident. The accident is consistent with the lower actuator support bracket loosening due to the failure of maintenance personnel to complete all necessary steps of the SB, and they likely failed to properly inspect the lower actuator bearing support bracket as directed in the manufacturer’s inspection guidance during the most recent inspection(s).

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Inspection of A185 brackets for fretting or looseness could have prevented failure.

NTSB coding

Evidence available

  • Photos
  • 9 docket documents
View NTSB final reportView NTSB docket

Docket documents9

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