San Antonio, TX, USA
N440AH
Robinson R44
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).
On December 14, 2019, about 1656 central standard time, a Robinson R44 II helicopter, N440AH, was substantially damaged when it was involved in an accident near San Antonio, Texas. The pilot and two passengers received minor injuries. The helicopter was operated as a Title 14 Code of Federal Regulations Part 91 revenue sightseeing flight. According to the pilot, he performed the daily inspection in the morning and a pre-flight inspection before the block of tours on the day of the accident. The accident flight departed Stinson Municipal Airport (SSF), San Antonio, Texas, about 1650. The pilot stated that after takeoff he climbed to 300 ft above ground level (agl) before turning north toward downtown. He climbed through about 650 ft agl, along the San Antonio River when he heard a single faint “bang” almost immediately followed by a very loud “bang.” The engine’s sound increased, and the tone changed significantly. The nose of the helicopter began to yaw to the left and then he felt the helicopter begin to descend. He immediately entered an autorotation and began maneuvering to the safest place to land. He made a “MAYDAY” call to SSF tower and began a quick briefing to the passengers. During the descent, he could see power lines, so he manipulated the controls to gain what altitude he could to clear the tallest lines and continued toward a road intersection. The main rotor mast then contacted a small guy wire and two smaller utility lines, pulling the helicopter onto its left side prior to impacting the ground and resulting in substantial damage to the helicopter fuselage, main rotor, tail boom and tail rotor. A postaccident examination revealed that the upper and lower belt tension actuator bearing support brackets (A185 brackets) were separated from the fan scroll. In addition, the belt tension actuator remained connected to the lower bearing and drive shaft assembly but had shifted out of alignment. The actuator screw tube was bent, and the actuator over-travel safety shutoff switch was engaged. A portion of the fan scroll was removed for examination. It had been cut out from the main scroll assembly by on-scene investigators. The removed portions of the upper scroll and lower scroll, along with the A185 brackets were included in the shipment to the manufacturer for further examination. The upper brackets (A185) were separated from the scroll. There were two holes in each bracket. Both rivets in each bracket appeared to be sheared flush with the contact face of the bracket. Both bracket contact surfaces and sheared rivets had a shiny bright surface. Three of the four rivet heads were smeared. On the mating surface of the upper scroll, all four holes were elongated (see figure), and the surface was worn under each bracket and the inside back plate. The two upper scroll back plates were not recovered on-scene. Figure - Upper scroll (reverse side) closeup. The lower bracket remained attached to the lower scroll. Fiberglass damage was evident on the left side of the bracket. Non-factory backing plates had been used on the back side. The scroll area around the lower bracket appeared to have a fiberglass repair. Paint surface on the upper portion of the bracket (bracket to bearing housing surface) had worn through on the inboard edge. A review of the aircraft records revealed manufacturer service bulletin (SB) 94, Subject: Actuator Lower Bearing A185 Brackets, issued June 8, 2017, and accomplished at an aircraft total time of 2813.78 hours on November 24, 2017. SB 94 was addressed to R44 series owners, operators, and maintenance personnel and directed 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 was 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. The records also revealed the most recent 100-hour/annual inspection was completed on September 21, 2019, at a total airframe time of 3,380.27 hours. The total airframe time at the time of the accident was 3,439.00 hours. Service Letter (SL) 61A, dated July 21, 2017, was addressed to R44 series owners, operators, and maintenance personnel. The service letter directed 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. A maintenance logbook entry dated November 24, 2017, noted SB 94 had been complied with in accordance with SL 61; however, examination of the brackets revealed that a third rivet had not been installed as required. RHC MM §2.410, 100-hour inspection required an inspection 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 looseness and wear.
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.
Source: NTSB Aviation Accident Database
Aviation Accidents App
In-Depth Access to Aviation Accident Reports
