Summary
This document proposes the supersedure of an existing airworthiness directive (AD), applicable to all Fokker Model F28 Mark 0100 and 0070 series airplanes, that currently requires revising the Airplane Flight Manual (AFM) to include information that will enable the flightcrew to identify failures of the emergency direct current (DC)/alternating current (AC) bus power supply and to take appropriate corrective actions. That AD was prompted by one report indicating that a diode failed, which resulted in battery drain and loss of the emergency DC bus power supply; and another report indicating that the circuit breaker of the transformer rectifier unit No. 3 tripped, which resulted in the loss of the emergency DC/AC bus power supply. This action would require a new terminating modification for the existing AFM revisions. This action would also require a new AFM revision to inform the flightcrew that, under certain conditions, an ``EMER DC BUS'' warning on the multi-function display unit (MFDU) will occur, and to take appropriate corrective actions. The actions specified by the proposed AD are intended to prevent failures of the emergency DC/AC bus power supply, which could reduce the ability of the flightcrew to control the airplane.