Federal investigators say the engines of the commuter plane that crashed, killing former Sen. John Tower and 22 others, apparently were running at the time of impact.

Witnesses had reported the Atlantic Southeast Airlines plane was making unusual noises Friday before it went down in the woods.Damage to seven propeller blades suggests the propellers were spinning at the time of impact, meaning the engines were working, Susan Coughlin, vice chairman of the National Transportation Safety Board, said Sunday.

The type of plane, a Brazilian-made Embraer Brasilia 120, has a history of propeller overspeed, which Coughlin defined as running up to 50 percent faster than normal. Propeller overspeed can cause propeller and engine damage.

But Coughlin said of Friday's accident, "At this time there is no indication that propeller overspeed was a factor in this crash."

Since the craft was introduced in 1985, there have been seven or eight instances of propellers operating above maximum recommended levels, said chief NTSB investigator Barry Strauch. But he said those planes all landed safely.