OMF Symphony-FAA Airworthiness Directive-Garmin transponders

    OMF Symphony-FAA Airworthiness Directive-Garmin transponders
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    • Create Date August 25, 2018
    • Last Updated August 25, 2018

    Summary: The FAA is adopting a new airworthiness directive (AD) to supersede Airworthiness Directive 2004-10-15, which applies to certain GTX 330 and GTX 330D Mode S transponders that are installed on airplanes. AD 2004-10-15 currently requires you to install GTX 330/330D Software Upgrade Version 3.03, 3.04, or 3.05. This AD applies to certain GTX 33, GTX 33D, GTX 330, and GTX 330D Mode S transponders that are installed on airplanes and is the result of observations that the GTX 33/33D/330/330D may detect, from other airplanes, the S1 (suppression) interrogating pulse below the minimum trigger level (MTL) and, in some circumstances, not reply. The GTX 33/33D/330/330D should still reply even if it detects S1 interrogating pulses below the MTL.

    Consequently, this AD would require you to install a GTX 33/33D/330/330D Software Upgrade to at least Version 3.06. No additional action is necessary for those airplanes that have transponders Software Upgrade 3.03 installed. Software Upgrade Versions 3.03 and 3.06 correct a TAS, TCAD, and TCAS I system ''whisper-shout'' problem that could potentially lead to the aircraft not being visible at certain ranges. TCAS II systems are not affected. We are issuing this AD to prevent interrogating aircraft from possibly receiving inaccurate replies due to suppression from aircraft equipped with the GTX 33/33D/330/330D Mode S transponders when the pulses are below the MTL.


    The inaccurate replies could result in reduced vertical separation.

    Affected aircraft: Symphony OMF–100–160.

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    Omar Filipovic
    Omar Filipovic is president of the Glasair Aircraft Owners Association as well as the chief tinkerer and content editor for this website. He is also the web editor for Kitplanes Magazine. Omar is building a GlaStar in Portland, Oregon.