NTSB Identification: CEN10LA560
14 CFR Part 91: General Aviation
Accident occurred Monday, September 20, 2010 in Schaumburg, IL
Probable Cause Approval Date: 05/16/2011
Aircraft: SCHWEIZER 269C, registration: N34LB
Injuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

While the helicopter was hovering prior to departure for a routine training flight, a bolt and its associated hardware for the left aft cluster fitting of the tail boom assembly departed the helicopter. Subsequently, the instructor initiated a forced landing and the helicopter came to rest upright. Examination of the bolt and lock nut revealed incomplete threads at the pinch point of the locking stake due to a manufacturing defect. The bolt and lock nut assembly were installed as part of an aft cluster fitting modification that was performed about 4 months and 216 operational hours prior to the accident. As a result of the accident, the Federal Aviation Administration issued an Emergency Airworthiness Directive for owners to check the lock nuts.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The in-flight separation of the left aft cluster fitting assembly following the loss of torque on the lock nut due to a manufacturing defect.

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