WASHINGTON — 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 says 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.