Airworthiness Directives; LITEF GmbH Attitude Heading System (AHRS) Unit Model LCR-92, LCR-92S, and LCR-92H

This amendment adopts a new airworthiness directive (AD) that is applicable to LITEF GmbH Attitude and Heading Reference System (AHRS) Unit Model LCR-92, LCR-92S, and LCR-92H installed on but not limited to Sikorsky Aircraft Model S-76 helicopters, McDonnell Douglas Helicopter Systems Model MD-900 helicopters, Bell Helicopter Textron, Inc. Model 412 helicopters, and Pilatus Model PC-12 airplanes. This action requires either installing a placard adjacent to each primary attitude indicator which states that flight is limited to Visual Flight Rules (VFR) operations only, or modifying and inspecting the AHRS wiring cables, requiring a repetitive inspection of the cable shielding, and inserting a statement into the aircraft flight manual. This amendment is prompted by a field report and verified by laboratory tests that shows there is an unusual AHRS reaction to certain radio frequency signals. The actions specified by this AD are intended to prevent reliance on or to correct the cause of misleading roll and pitch information produced by the AHRS when encountering certain radio frequency signals.