Summary
We propose to adopt a new airworthiness directive (AD) for Eurocopter Deutschland GMBH (ECD) Model MBB-BK 117 C-1 and C-2 helicopters. This proposed AD would require installing a placard that corresponds to the maximum permissible flight altitude, amending the Rotorcraft Flight Manual (RFM) to revise the maximum permissible operating altitude, and inserting revised performance charts into the RFM. The proposed AD would also require a repetitive maintenance "MAX N1 CHECK'' to determine the appropriate maximum altitudes. The AD would also require, if the engine or a fuel control unit (FCU) or module 2 or 3 is replaced, repeating the maintenance "MAX N1 CHECK.'' Finally, the proposed AD specifies that modifying both engines would provide terminating action for the proposed AD requirements. This proposed AD is prompted by the failure of a "few'' engines to reach the specified one-engine-inoperative (OEI) rating at altitudes above 10,000 feet. The proposed actions are intended to prevent flights at altitudes where the full OEI engine power cannot be reached and subsequent loss of control of the helicopter if an OEI operation is required.