Airworthiness Directives; Airbus SAS Airplanes

We propose to adopt a new airworthiness directive (AD) for certain Airbus SAS Model A318 and A319 series airplanes; Model A320- 211, -212, -214, -231, -232, and -233 airplanes; and Model A321-111, - 112, -131, -211, -212, -213, -231, and -232 airplanes. This proposed AD was prompted by reports of false resolution advisories (RAs) from certain traffic collision avoidance systems (TCASs). This proposed AD would require modification or replacement of certain TCAS processors. We are proposing this AD to address the unsafe condition on these products.