Airworthiness Directives; ATR-GIE Avions de Transport Régional Airplanes

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The FAA is adopting a new airworthiness directive (AD) for certain ATR--GIE Avions de Transport R[eacute]gional Model ATR42-500 and ATR72 airplanes. This AD was prompted by an investigation indicating that an erroneous monitoring of the travel limitation unit (TLU) could occur when the airplane is flying above a certain speed as a result of the logic input from either air data computer (ADC) 1 or ADC2 input. This AD requires modifying airplanes by installing one or two relays and associated wiring and testing of the TLU monitoring logic. The FAA is issuing this AD to address the unsafe condition on these products.