Load shedding

Based on the reported weather at Carbondale, it should have been apparent that he would need electrical power to operate his radio navigation instruments on arrival since he most probably would have to execute an instrument approach to land. Therefore, to insure that he could complete the 39-minute flight to Carbondale, all unnecessary electrical loads would have to be shed in order to have residual electrical power. In addition, there was no way the captain could determine the exact charge state of the batteries when the generators failed; therefore, even with proper load shedding procedures, the captain could not have been sure that battery power would last longer than 30 minutes. Given the two options available to the captain when the generators failed, the risks involved in continuing to Carbondale were such that this option should have been rejected summarily.

Early in the SR 111 investigation, it was discovered that the Swissair MD-11 in-flight entertainment network (IFEN) was connected to aircraft power in such a way that was not compatible with the emergency electrical load-shedding design philosophy of the MD-11 aircraft. The IFEN was powered from AC Bus 2, a bus that is not deactivated when the CABIN BUS switch is selected. Use of the CABIN BUS switch, which was the first item in Swissair’s Smoke/Fumes of Unknown Origin Checklist at the time of the occurrence, is intended to remove most electrical power from the aircraft cabin.