Summary
We propose to adopt a new airworthiness directive (AD) for all Eurocopter Deutschland GmbH (ECD) EC 135 P1, P2, P2+, T1, T2, and T2+ helicopters equipped with a certain main transmission housing upper part. This proposed AD would require installing a corrugated washer in the middle of the main transmission filter housing upper part and modifying the main transmission housing upper part. This proposed AD is prompted by an inspection of housing upper parts that revealed the bypass inlet in the oil filter area was not manufactured in accordance with applicable design specifications. The proposed actions are intended to prevent failure of the main transmission and subsequent loss of control of the helicopter.