Action
Final rule; request for comments.
Summary
We are publishing a new airworthiness directive (AD) for Airbus Helicopters Model MBB-BK 117 A-3, MBB-BK 117 A-4, MBB-BK 117 B- 1, and MBB-BK 117 C-2 helicopters with a certain Metro Aviation, Inc. (Metro), vapor-cycle air conditioning kit pulley (pulley) installed, which was sent previously to all known U.S. owners and operators of these helicopters. This AD supersedes AD 2013-12-06, which required inspecting the pulley for looseness and properly installed lockwire and re-installing the pulley. Since we issued AD 2013-12-06, we received a report of a possible design and manufacturing deficiency in some pulleys wherein they did not have sufficient thread depth, allowing the pulley to detach from the rotor brake disc. This AD requires inspecting each pulley attaching bolt hole to determine if there is sufficient depth of the threads and either removing the pulley if the depth is insufficient or installing dual locking tabs under each pulley attaching bolt if the depth is sufficient. These actions are intended to prevent the pulley from detaching, resulting in damage to the tail rotor (T/R) driveshaft, and subsequent loss of control of the helicopter.