Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to all Fokker Model F27 Mark 100, 200, 300, 400, 500, 600, and 700 series airplanes. This proposal would require a one-time inspection for correct installation of the left-and right-hand fuel differential pressure (FDP) switches and for correct connection of the pressure sensing lines to the switches. It would also require corrective action, if necessary. This action is prompted by reports of incorrect installation of the FDP switches and the resulting cross-connection of the pressure sensing lines to those switches. This action is necessary to ensure that a warning light goes on when the fuel filter is partially blocked by ice, so that the blockage of the fuel filter does not increase, leading to reduced fuel flow to the engine and possibly to an engine flame-out. This action is intended to address the identified unsafe condition.