Summary
We are revising an earlier proposed airworthiness directive (AD) for certain McDonnell Douglas Model MD-90-30 airplanes. The original NPRM would have required replacement of the wire harness of the auxiliary hydraulic pump with a new wire harness, and routing the new wire harness outside of the tire burst area. The original NPRM resulted from fuel system reviews conducted by the manufacturer, as well as reports of shorted wires in the right wheel well and evidence of arcing on the power cables of the auxiliary hydraulic pump. This action revises the original NPRM by proposing to require modifying the auxiliary hydraulic power system (including doing all applicable related investigative and corrective actions). We are proposing this supplemental NPRM to prevent shorted wires or electrical arcing at the auxiliary hydraulic pump, which could result in a fire in the wheel well. We are also proposing this supplemental NPRM to reduce the potential of an ignition source adjacent to the fuel tanks, which, in combination with flammable fuel vapors, could result in a fuel tank explosion and consequent loss of the airplane.