Bell UH-1H crash near Mesa, AZ, United States

HISTORY OF FLIGHTOn April 24, 2020, about 1600 mountain standard time, a Bell UH-1H helicopter, N3276T, was substantially damaged when it was involved in an accident in Mesa, Arizona. The pilot was fatally injured, and the second pilot was seriously injured. The helicopter operated as a Title 14 Code of Federal Regulations (CFR) Part 91 relocation flight. The surviving pilot stated he does not recall the accident sequence. Witnesses reported they observed the helicopter flying low toward Falcon Field Airport (FFZ), Mesa, Arizona, with white smoke emitting from the tail rotor area. Suddenly, the tail rotor separated from the helicopter and landed in a dirt lot below. The helicopter continued northeast as it started to spin and impacted the ground. The flight track indicated that the helicopter took off from Jacqueline Cochran Regional Airport (TRM), Palm Springs, California, about 1324 Pacific daylight time and turned eastbound seemingly along Interstate I-10 toward the Phoenix area. The flight track was intermittent due to the helicopter going in and out of coverage for about 2 hours before passing just north of Buckeye Municipal Airport (BXK) Buckeye, Arizona. The helicopter then turned right and tracked southeast for about 10 minutes and turned left traveling east over a mountain chain and continuing until reaching Stellar Airpark (P19), Chandler, Arizona. The helicopter performed one left hand 360° turn just west of the field before continuing across the airport and turning northeast directly toward FFZ. The helicopter continued along that heading until just before crossing Highway 60 when it began to simultaneously descend and lose ground speed. After crossing the highway, it entered a right descending turn until track data were lost about 1556. AIRCRAFT INFORMATIONAccording to aircraft records, the accident helicopter’s tail rotor gearbox (also known as the 90-degree gearbox) was removed from a different helicopter in September 2012 due to failing serviceability checks caused by metal accumulation. In November 2012, it was repaired by replacing the main input seal, painted, and installed onto the accident helicopter, about 228 flight hours prior to the accident. There was no other information regarding this installation. In January 2019, the helicopter’s tail boom, upper portion of the vertical stabilizer, and elevators were painted. Photographs from this painting activity showed that the tail boom, tail rotor gearbox, and tail rotor assembly remained installed during the painting process. The tail rotor assembly and tail rotor gearbox were masked during the painting process. The fuselage and lower tail boom were painted a white color, and the upper portion of the tail boom was painted black. The vertical stabilizer was painted black on the upper and lower portions, with a blue stripe in the middle. The elevators were removed from the tail boom and painted separately; they were painted a blue color. In April 2019, about 39 flight hours prior to the accident, the tail rotor gearbox was removed from the vertical stabilizer for a corrosion inspection; no defects were noted in the maintenance logs. The United States Army technical manuals, cited by the type certificate holder for maintenance of this helicopter, do not require a retorque and/or torque stabilization check of gearbox retaining nuts a certain number of flight hours after installation. In December 2019, about 7 hours prior to the accident, oil was drained from the tail rotor gearbox due to discoloration and samples were sent for oil analysis. The oil analysis report indicated abnormal copper and aluminum wear particles within the tail rotor gearbox oil. While no corrective action was recommended at that time, a resample was recommended at the next service interval. The accident occurred before the next oil sample was taken. AIRPORT INFORMATIONAccording to aircraft records, the accident helicopter’s tail rotor gearbox (also known as the 90-degree gearbox) was removed from a different helicopter in September 2012 due to failing serviceability checks caused by metal accumulation. In November 2012, it was repaired by replacing the main input seal, painted, and installed onto the accident helicopter, about 228 flight hours prior to the accident. There was no other information regarding this installation. In January 2019, the helicopter’s tail boom, upper portion of the vertical stabilizer, and elevators were painted. Photographs from this painting activity showed that the tail boom, tail rotor gearbox, and tail rotor assembly remained installed during the painting process. The tail rotor assembly and tail rotor gearbox were masked during the painting process. The fuselage and lower tail boom were painted a white color, and the upper portion of the tail boom was painted black. The vertical stabilizer was painted black on the upper and lower portions, with a blue stripe in the middle. The elevators were removed from the tail boom and painted separately; they were painted a blue color. In April 2019, about 39 flight hours prior to the accident, the tail rotor gearbox was removed from the vertical stabilizer for a corrosion inspection; no defects were noted in the maintenance logs. The United States Army technical manuals, cited by the type certificate holder for maintenance of this helicopter, do not require a retorque and/or torque stabilization check of gearbox retaining nuts a certain number of flight hours after installation. In December 2019, about 7 hours prior to the accident, oil was drained from the tail rotor gearbox due to discoloration and samples were sent for oil analysis. The oil analysis report indicated abnormal copper and aluminum wear particles within the tail rotor gearbox oil. While no corrective action was recommended at that time, a resample was recommended at the next service interval. The accident occurred before the next oil sample was taken. WRECKAGE AND IMPACT INFORMATIONOn scene examination by a Federal Aviation Administration inspector indicated that the debris field was about 1/2 mile long, extending along a generally northeast direction. The first identified pieces of debris were fragments of glass, which were consistent with a vertical stabilizer navigation light. About 200 yards further northeast were the tail rotor assembly and the input quill assembly. The rest of the helicopter came to rest about ½ mile further northeast in an open, slightly sloped field. The first pieces of debris in the field were the vertical stabilizer and a large portion of the right elevator. Next were two long and narrow ground strikes, consistent with main rotor blade strikes. Immediately following this area was the main wreckage; the helicopter came to rest slightly nose- and left-side low, along a heading of about 49°. The helicopter exhibited upward crushing throughout the cabin and fuselage, most extensively on the left side of the fuselage. The mast and the main transmission were displaced forward and to the left. The main rotor assembly was fracture separated and located about 20 yards northeast of the main wreckage; it was the last major piece of debris. Postaccident examination of the helicopter’s engine did not reveal any anomalies that would have precluded normal operation. Flight control continuity was mostly established throughout the airframe; some areas were inaccessible due to airframe deformation. The tail boom had been removed for recovery purposes. The vertical stabilizer was fracture-separated, consistent with main rotor blade impact. The tail rotor gearbox was fracture-separated at the attachment studs, and four of the fractured attachment stud pieces were found loose within the vertical stabilizer. A fifth stud piece remained stuck in the vertical stabilizer support casting, and the nut end of the sixth stud piece was not located. The chip detector was removed from the tail rotor gearbox and metallic debris was present. The tail rotor