AD FAA-2013-0018

We are adopting a new airworthiness directive (AD) for Eurocopter Deutschland GmbH (Eurocopter) Model MBB-BK 117 C-2 helicopters. This AD requires determining if a certain serial-numbered bevel gear is installed in the tailrotor intermediate gear box (IGB). If such a bevel gear is installed in the IGB, this AD requires recording the bevel gear's reduced life limit in the Airworthiness Limitations section of the maintenance manual and on the component history card or equivalent IGB record. If the bevel gear's life limit has been reached or exceeded, this AD requires, before further flight, replacing the bevel gear with an airworthy bevel gear. This AD is prompted by the discovery that the tooth foot fillets in certain bevel gears fall below the minimum dimensions required in the design documents to ensure safe functioning of the bevel gear until it reaches its approved life limit. This AD's actions are intended to prevent failure of a bevel gear before it reaches its currently approved life limit, failure of the IGB, and subsequent loss of helicopter control.