Garmin issued a service alert on Wednesday warning users of some of its brand-new GNS 430 and GNS 430A units not to use them for IFR operations. It was the company’s second service alert this month to include those units. The panel-mounted units have a problem that could cause the unit to trip the aircraft circuit breaker, rendering the unit inoperative, Garmin said. Only units manufactured between Feb. 23, 2005, and March 21, 2005, are affected. If you have an affected GNS 430 unit, contact your local Garmin authorized service center immediately, and they will make arrangements to modify or replace the unit, Garmin said.