Trona Airport, Trona, CA
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Airport Area Accident History:
Accident occurred Saturday, September 03, 2005
in Trona, CA
Probable Cause Approval Date: 2/26/2007
Aircraft: Goodlett Safari, registration: N912TT
Injuries: 1 Minor.
The experimental helicopter impacted terrain
after experiencing a failure of a
flight control connecting rod. According
to the pilot, he was maneuvering the helicopter
about 50 feet above the ground when he heard a
loud bang followed by a whirring or buzzing
noise. The helicopter rolled to the left, which
the pilot was unable to counter with control
inputs, and impacted terrain on the left side. A
post-accident examination of the helicopter by
the pilot/builder revealed that a 27.875-inch
aluminum
control rod was fractured near the middle
of the rod. The control rod was connected
between the collective-cyclic mixing assembly
and a walking beam that connected to the
stationary swash plate of the left side (pilot
side) of the helicopter. The break in the
control rod was perpendicular to the
longitudinal axis of the rod. Examination of the
control rod by a
metallurgical laboratory revealed the
failure was a result of a fatigue crack that had
propagated through nearly 75 percent of the
control rod. A portion of the break was polished
indicating that the crack had been present for
quite some time. The pre-existing crack in the
control rod reduced its strength to a point that
allowed the
flight control forces to fail the
remaining material. According to the
pilot/builder, a break in the control rod would
result in flight characteristics consistent with
that experienced by the pilot during the
accident flight. The control system has been
redesigned by the kit manufacturer as a result
of this accident and now incorporates steel
control rods as opposed to aluminum ones.
The National Transportation Safety Board
determines the probable cause(s) of this
accident as follows:
the in-flight fatigue failure of a control
system connecting rod, which resulted in a loss
of helicopter control.
Trona
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