AD NUMBER: 2005-22-01
MANUFACTURER: Sikorsky SUBJECT: Airworthiness Directive 2005-22-01 SUMMARY: This amendment adopts a new airworthiness
directive (AD) for the Sikorsky Aircraft Corporation (Sikorsky)
Model S-76A, B, and C helicopters. This action requires certain
inspections of the main rotor lower bifilar arm assembly in the
attachment area around the lower bifilar lugs for a crack.
If a crack is found on any bifilar lug, this AD requires
replacing the bifilar arm assembly with an airworthy bifilar arm
assembly. If no crack is found, this AD requires a one-time test
for the required torque on the lug nuts and, if necessary, applying
the required torque and conducting the torque stabilization tests.
This amendment is prompted by four reports of cracked bifilars. The
actions specified in this AD are intended to prevent failure of a
bifilar lug, damage to the main rotor control system, and
subsequent loss of control of the helicopter.