In December 2000 the US Army grounded its entire AH-64 Apache
helicopter fleet as a precautionary measure, following the
discovery of a faulty tail rotor swashplate assembly. Failure of a
tailrotor swashplate assembly, which produces yaw control, could
result in the loss of an aircraft and crew injuries. The Army
ordered an inspection of all 742 AH-64A and D aircraft to locate
specific swashplate assemblies identified as being potentially
faulty, which would be replaced.
Most likely the swashplate assembly got detached and sliced off
the tail section. 
