Airworthiness Directives; MD Helicopters, Inc. Model MD900 Helicopters

This amendment supersedes an existing airworthiness directive (AD) that applies to MD Helicopters, Inc. (MDHI) Model MD900 helicopters. That AD currently requires turning ON both Vertical Stabilizer Control System (VSCS) switches and turning OFF the autopilot (AP/SAS) switch; pulling certain AP/SAS circuit breakers; installing a placard near the AP/SAS master switch; installing an airspeed limitation placard on the instrument panel; and making changes to the Rotorcraft Flight Manual (RFM). This amendment retains those requirements and provides an option of replacing each affected tube adapter with a newly-designed tube adapter, which provides terminating action for the unsafe condition. This amendment is prompted by the manufacturer introducing an improved, newly-designed tube adapter. The actions specified by this AD are intended to prevent loss of yaw control and subsequent loss of control of the helicopter.