WPR19LA028

The pilot of the sightseeing helicopter flight reported that he experienced a loud thump immediately followed by vibration and that he chose to conduct a precautionary landing at a nearby airport. Postaccident examination of the tail rotor components revealed that one of the tail rotor blades’ root enclosures, along with its associated weights and attachment bolts, had separated. The other tail rotor blade sustained a 6-inch-long dent about mid-span when the root enclosure separated. About 200 flight hours before the accident, the subject tail rotor blade was removed from service due to a delamination of the root enclosure at the root block and a repair was made of the blade’s root enclosure area. Scratches were observed on the root block around the edge of one of the tail rotor blades’ root enclosure areas, consistent with surface preparation for the repair. However, while the surface preparation with the scratches created an appropriate bonding surface, the adhesive did not properly bond to the remaining area of the faying surface due to corrosion. Additionally, no adhesive was applied into the gap between the root enclosure and root block. This action would require the surface in that area to be prepped for the application of the adhesive, and no evidence of such preparation was observed. The surface of the root block to where the enclosure was bonded was corroded with paths of oxidation extending outboard, consistent with trapped moisture between the adhesive and the enclosure, which eventually resulted in the enclosure separating from the root block.

On October 27, 2018, about 1104 Hawaiian standard time, a Bell 430 helicopter, N430ST, was substantially damaged when it was involved in an accident near Kailua/Kona, Hawaii. The commercial pilot and three passengers were not injured. The helicopter was operated as a Title 14 Code of Federal Regulations Part 135 revenue sightseeing flight. According to the pilot, he was transitioning offshore to fly around the island of Hawaii. The autopilot was engaged and was commanded to climb the helicopter to 1,500 ft mean sea level (msl). The pilot reported that when the helicopter was at an altitude of 1,350 ft msl, a speed of 125 knots, and a heading of about 165°, he experienced a loud thump immediately followed by a medium-to-high-frequency vibration of significant amplitude. He further reported that he felt the vibration through the airframe more than through the flight controls. The pilot conducted a precautionary landing at Ellison Onizuka Kona International Airport at Keahole, Kailua/Kona, Hawaii. The landing was uneventful, but the vibrations increased in intensity when the throttles were reduced to idle while on the ground. The pilot performed a normal engine shutdown, and the occupants safely egressed. Postaccident examination of the tail rotor components revealed that one of the tail rotor blades’ root enclosures, along with the associated weights and attachment bolts, had separated. The other tail rotor blade sustained a 6-inch-long dent about mid-span. Components from the tail rotor blade and hub assembly were shipped to the helicopter manufacturer for examination. Examination revealed that one of the blades’ tail root enclosures had separated from the inboard edge portion of the blade. The other blade damage was consistent with impact damage from contact with the separated root enclosure. A review of the maintenance records revealed that about 200 flight hours before the accident, the subject tail rotor blade was removed from service due to a partial delamination of the root enclosure at the root block. A repair was made where the blade’s root enclosure was bonded to the root block. Scratches were observed around the edge of the repair area consistent with surface preparation for the repair; however, while the surface preparation with the scratches created an appropriate bonding surface, the remaining area where the adhesive was in contact with the blade surface was corroded, and the adhesive did not properly bond in this area. There was no additional adhesive or evidence of surface preparation observed in the gap between the root enclosure and root block. On the area opposite the root enclosure, on the leading edge of the blade, paint work was present consistent with the root enclosure being clamped to the root block during the repair. The surface of the root block to where the tang enclosure was bonded was corroded with paths of oxidation extending outboard, consistent with moisture between the adhesive and the blade enclosure. Aspectroscopy examination of the tail rotor blade root block revealed that the material was similar in composition to the specified alloy, and the hardness measured value conformed to the specified minimum hardness value. A sample of the adhesive was examined by Bell Chemical and Processes Laboratory. The material was consistent with the original adhesive used during manufacture and was determined to be chemically similar to the specified adhesive. Examination of the adhesive used to bond the enclosure at the time of manufacture revealed that the cure percentage was about 97%, which was consistent with a fully cured adhesive. The adhesive used in the repair was not located on the surface areas that were prepared. The root balancing weight plate damage was also examined. At some undetermined point, both of the end portions of the closed-end nuts used to attach the tail rotor balancing weights to the nut plate had penetrated into the honeycomb structure, leaving a 1-inch void. The investigation was unable to determine what caused voids in the honeycomb. However, this anomaly exhibited no damage beyond the 1-inch void bore in the honeycomb.