Bell UH-1V accident near Cordes Lakes, Arizona, September 21, 2013

The NTSB's narrative final · quoted from the NTSB record

About 5 months before the accident, the pilot purchased the former military helicopter, which he was operating as an experimental aircraft in the exhibition category, and had flown it about 33 hours. On the day of the accident, during cruise flight, about 2,000 ft above ground level, the main rotor (MR) mast failed, and the MR hub and blade assembly separated from the helicopter. The primary debris trail was relatively linear and extended a distance of about 2,000 ft. Examination of the recovered wreckage revealed that five components of one MR blade's pitch control system, including a rotary damper assembly, were missing. Several subsequent searches of the accident site were unsuccessful in locating the missing components. The inability to locate these five components, combined with the damage patterns on neighboring components that were recovered, suggested that the components' separation was the precipitating event in the accident sequence. It is likely that one or more of the missing components either failed or otherwise became detached, which resulted in a loss of MR blade pitch control, mast bumping, and mast failure. For most of the 9 years before its purchase, the helicopter had been on display in a museum and was flown infrequently. After acquiring the helicopter, the pilot contacted several people who were knowledgeable about this make and model helicopter to solicit maintenance advice and/or services. Interviews of these people and review of available records indicated that the pilot, who was not an FAA-certificated aircraft mechanic, conducted a majority of the maintenance activity on the helicopter. The pilot purchased multiple used components of unknown airworthiness and at least one of these components, a rotary damper assembly, was installed on the MR blade pitch control system by the pilot about 2 months before the accident. However, incomplete component purchase and aircraft maintenance records prevented the investigation from determining whether that damper was still installed on the day of the accident and exactly what maintenance the pilot had performed on the MR blade pitch control system. The pilot's limited maintenance qualifications and experience decreased the likelihood that he would detect nonairworthy conditions or components and increased the risk of improper repairs. It is likely that the inflight separation of the MR hub and blade assembly was precipitated by the pilot's improper maintenance actions on the MR blade pitch control system.

The complete narrative as the NTSB published it. The NTSB's docket holds the report as a PDF and any photographs, statements and other documents from the investigation.