Airworthiness Directives; MD Helicopters, Inc. Model 500N and 600N Helicopters

This document supersedes AD 2008-18-52 and publishes in the Federal Register an amendment adopting Emergency Airworthiness Directive (AD) 2008-22-52 which was sent previously to all known U.S. owners and operators of MD Helicopters, Inc. (MDHI) Model 500N and 600N helicopters by individual letters. This AD requires turning OFF the Yaw Stability Augmentation System (YSAS); installing a placard that limits airspeed to 100 KTS or V<INF>NE</INF>, whichever is less; and revising the limitations section of the Rotorcraft Flight Manual (RFM) to reflect that limitation. Finally, replacing the adapter tubes with airworthy adapter tubes that have a production date code stamp is required. This AD is prompted by several occurrences of failed adapter tubes on the Model MD900 helicopter which uses the same adapter tubes. The actions specified by this AD are intended to prevent loss of yaw control and subsequent loss of control of the helicopter.