Robinson Helicopter R22 BETA II N4160A accident near Fillmore, California

Probable cause

An in-flight break-up while maneuvering as a result of the main rotor blades diverging from the normal plane of rotation and severing the tailboom. The underlying reason for the main rotor divergence could not be determined.

NTSB analysis

The operator reported that the pilot had rented the helicopter for a personal proficiency flight to the local practice area. No eyewitnesses to the accident sequence were located. Documentation of the accident site noted that pieces of the tailcone, tailrotor flight controls, and tailrotor driveshaft were located about 900 feet away from the main wreckage at a location consistent with the main rotor blade contacting the tailcone while in flight. Inspection of the outboard end of the main rotor blades found red scuff marks, which appeared to match the red “Danger” decal on the tailcone. Evidence of black scuff marks consistent with the paint scheme of the main rotor blades were also noted on pieces of the tailcone. During the postaccident examination of the airframe and control system, there was no evidence found that would explain the main rotor disc's divergence from the normal plane of rotation and its subsequent contact with the tailboom. No evidence of a preimpact mechanical malfunction was observed during the examination of the engine, the airframe, or control systems.

Text from the NTSB. Open the NTSB docket for WPR09FA104 for the full record.