WASHINGTON (AP) — Orders to U.S. factories fell in August, mostly because of a sharp drop in volatile aircraft orders. The decline offset an increase in orders that reflect corporate investment plans.

The Commerce Department said Thursday 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. That pulled down orders for long-lasting manufactured goods by 13.2 percent.

In one positive sign, orders for business equipment and software, often considered a proxy for investment plans, rose 1.1 percent, after two steep declines.

The value of orders for non-durable goods, which include food, clothing, and gas, 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. Factories received more new orders in September and also increased hiring. That indicates that factory activity may recover after a summer slowdown.