NTSB Identification: ANC06LA038.
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Accident occurred Wednesday, March 22, 2006 in Mesa, AZ
Probable
Cause Approval Date: 10/31/2006
Aircraft: MD Helicopters, Inc. MD 900,
registration: N912LH
Injuries: 2 Uninjured.

The experimental category flight was being operated by the helicopter
manufacturer under Title 14, CFR Part 91, when the accident occurred. The
commercial certificated helicopter pilot was conducting a series of climbing and
descending turns while a second helicopter, flying alongside, filmed the
maneuvers. According to a safety representative for the helicopter manufacturer,
all of the maneuvers were conducted within the normal limitations of the
helicopter. The maneuvers were completed uneventfully, with no in-flight
anomalies noted, and the helicopter returned to the manufacturer's base. While
conducting a routine daily inspection of the helicopter in preparation for the
next scheduled flight, maintenance technicians discovered damage to the main
rotor hub's five pitch case assemblies, slightly aft of the upper damper cap.
The damage was a result of the pitch cases striking the upper main rotor hub
perimeter bolts. All five pitch cases were damaged beyond repairable limits, and
were replaced. The safety representative for the helicopter manufacturer
reported that the anticipated corrective action will be to increase the
clearance between the pitch cases and the main rotor hub perimeter bolts by
trimming additional material from the inboard and upper portion of the main
rotor pitch case assemblies during the manufacturing process.

The National Transportation Safety Board determines the probable cause(s) of
this accident as follows:
The manufacturer's inadequate design clearance of
the main rotor blade grip pitch cases, which resulted in damage to the pitch
cases when they contacted main rotor perimeter bolts during maneuvering flight.

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