WASHINGTON (AP) — Orders to U.S. factories fell in August by the largest amount on record, but the drop was heavily weighed by an expected plunge in volatile aircraft orders. A key category that tracks business investment plans posted a small increase, offering an encouraging sign that factory production will sustain momentum in the second half of this year. Core capital goods, a category seen as a proxy for business investment, managed to rise a slight 0.4 percent in August after a 0.1 percent July dip. Orders for motor vehicles and parts dropped 5.4 percent, but that weakness was expected to be temporary given the robust sales automakers are experiencing this year.