Summary
We propose to adopt a new airworthiness directive (AD) for certain Rockwell Collins TDR-94 and TDR-94D Mode select (S) transponders that are installed on airplanes. This proposed AD was prompted by instances where the TDR-94 and TDR-94D Mode S transponders did not properly respond to Mode S Only All-Call interrogations when the airplane transitioned from a ground to airborne state. This proposed AD would require inspecting the setting of the airplane type code category strapping and require either modifying the airplane type code category setting or installing the software upgrade to convert the affected transponders to the new part number. We are proposing this AD to correct the unsafe condition on these products.