Transponder AD Requires Software Upgrade

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Owners of a popular brand of Mode S transponder must ensure they're running the proper software. The FAA has issued an Airworthiness Directive for Garmin GTX 330 and 330D Mode S transponders after it was discovered that, under certain circumstances, they don't always reply to the interrogation pulse of another aircraft. "The inaccurate replies could result in reduced vertical separation or unsafe TCAS resolution advisories," the AD says. The fix is to install Software Upgrade Version 3.03, 3.04 or 3.05. The transponders are installed in hundreds of different types of aircraft.