Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to certain Gulfstream Model G-1159A (G-III) series airplanes. This proposal would require modification of the master caution panel by installing an additional legend labeled "BATT ON BUS" and associated wiring to indicate when the airplane batteries are powering the direct current (DC) essential bus. This action is necessary to ensure that the flight crew is aware that an electrical system failure has occurred and that the main airplane batteries are powering the essential DC bus. If the flight crew is unaware of this situation, action to stop the depletion of the airplane batteries will not be taken and critical equipment, such as communications and navigation equipment, could fail. This action is intended to address the identified unsafe condition.