Airworthiness Directives; MD Helicopters, Inc. Model MD-900 Helicopters
This amendment supersedes an existing airworthiness directive (AD) for MD Helicopters, Inc. (MDHI) model MD-900 helicopters that currently requires applying serial numbers to certain parts, increasing the life limit for various parts, maintaining a previously established life limit for a certain vertical stabilizer control system (VSCS) bellcrank assembly and bellcrank arm, and correcting the part number for the VSCS bellcrank arm. This amendment requires the same actions as the existing AD, except it reduces the life limit of the swashplate spherical slider bearing (slider bearing). It further corrects what was described as a "bellcrank arm" life limit in the current AD and correctly describes it as another "bellcrank assembly" life limit. This amendment is prompted by two reports of cracks in the slider bearing that occurred well before the previously increased retirement life of 2,030 hours time-in-service (TIS) was reached. The actions specified by this AD are intended to establish appropriate life limits for various parts, and to prevent fatigue failure of those parts and subsequent loss of control of the helicopter.