Summary
This document proposes to adopt a new airworthiness directive (AD) that would apply to certain GARMIN International (GARMIN) GNS 430 units that are installed on aircraft. The proposed AD would require you to modify the unit to incorporate circuitry changes to the GNS 430 unit's deviation and flag outputs. The proposed AD is the result of reports of inaccurate course deviations caused by external electrical noise to the GNS 430 unit's course deviation indicator (CDI). The actions specified by the proposed AD are intended to prevent such external noise from causing inaccurate course deviation displays in the GNS 430 unit's CDI or horizontal situation indicator (HSI). Such displays could result in the pilot making flight decisions that put the aircraft in unsafe flight conditions.