This time the problem occurred when a US military flight strayed into disputed airspace near the islands, a senior US defense official told CNN on Friday.
The United States did not intend to get within 12 nautical miles of the land, the official said, and the flight was not part of a "freedom of navigation" mission like the one that occurred in late October.
Washington angered Beijing in October when a US warship sailed close to artificial islets that China is building out into military bases, in what the US called a "freedom of navigation" exercise.
Washington has said China's transformation of the geographical features in the Spratly Islands poses a threat to freedom of navigation in the critical area.