Orders to U.S. factories fell in August, mostly because of a sharp drop in volatile aircraft orders, a government report showed on Thursday. The Commerce Department said that factory orders fell 5.2 percent in August, the biggest drop in more than three years. The decline was largely because demand for commercial aircraft plunged 102 percent, pulling-down orders for long-lasting manufactured goods by 13.2 percent. In one positive sign, orders for business equipment and software rose 1.1 percent, after two steep declines. The value of orders for non-durable goods, which include food, clothing, and gas, also rose 2.2 percent, mostly because gas prices were higher. The manufacturing sector is sending mixed signals. The weak factory goods report suggests businesses are getting more cautious. But a survey of purchasing managers released Monday showed that manufacturing activity expanded in September after three months of declines. Also, auto sales jumped last month to nearly 1.2 million, an increase of 13 percent compared to a year earlier, signaling that consumers are still willing to spend on expensive goods, even as job growth remains weak.