Orders to American factories in November posted the largest increase in 14 months, but aircraft accounted for most of the gain and other industries showed signs of slowing as the new year approached.

The 2.5 percent advance to a seasonally adjusted $345.1 billion was the sixth in a row, the Commerce Department said Tuesday.

Transportation orders surged 21 percent, the most since July 1991. For aircraft alone, orders doubled. Economists said airlines around the world need to replace their aging planes.

“The fleet is getting old. It pollutes too much and makes too much noise. We know we’re going to have very strong aircraft orders for the next few years,” said economist David Orr of First Union Corp. in Charlotte, N.C.

However, excluding transportation, orders fell 0.3 percent in November, the second decline in a row. And capital goods - those such as factory machinery used to make other goods - fell 1.5 percent when transportation and defense orders are excluded.

“That may be one of the first signs that the Asian crisis is beginning to affect the U.S. markets given that about half the capital goods produced in the United States are exported,” said economist Cheryl Katz of Merrill Lynch.