Airworthiness Directive · Amendment 39-17483 · Tail rotor gearbox
Eurocopter Deutschland GmbH Helicopters
This AD applies to Model MBB-BK 117 C-2 helicopters with a bevel gear, part number (P/N) 4639 310 065, installed in the tail rotor intermediate gear box (IGB), P/N 4639 002 007, certificated in any category.
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.
You are responsible for performing each action required by this AD within the specified compliance time unless it has already been accomplished prior to that time.
Within 30 days, do the following:
(1) Determine if a bevel gear with a serial number (S/N) listed in Table 1 of Eurocopter Alert Service Bulletin MBB BK117 C-2-04A-005, Revision 2, dated April 28, 2010 (ASB), is installed in the IGB.
(i) If a bevel gear listed in Table 1 of the ASB is installed in the IGB, record the reduced life limit of the bevel gear onto the component history card or equivalent record of the IGB.
(ii) If the bevel gear life limit has been reached or is exceeded, before further flight, replace the bevel gear with an airworthy bevel gear.
(2) Revise the Airworthiness Limitations section of the maintenance manual by reducing the retirement life for each IGB bevel gear, P/N 4639 310 065, that has a S/N listed in Table 1 of the ASB to the life limit corresponding to that S/N.
The aircraft, engines and makers this AD names, by the model designations in its text. A model listed here may still be outside the AD's serial ranges.
