The engine fan hub that broke apart as a jetliner was accelerating for takeoff had an inch-deep pre-existing crack that probably caused the accident which killed two passengers, federal officials said Monday.

The hub had been used on another engine and then was installed seven months ago during repair of an oil leak on the engine involved in the accident, National Transportation Safety Board officials said.

Although no final determination has been made, the crack - evidence of metal fatigue - appears to have been the cause of the hub’s failure, said Michael Marx, senior metallurgist for the safety board.

“The crack is fairly substantial in size as it is now. It’s approximately one-inch deep,” Marx said at a news conference. “A crack of that size probably is sufficient to cause the separation of the disk.”

A Delta metallurgist did his own inspection and came to the same conclusion about the crack, said George Black, a safety board member.

“I don’t know that I’d call it ‘used,’ but it was a part of an engine that was sold to Delta Air Lines, I believe, in 1987,” Black said. “But it is not uncommon, I am told, to switch major components on engines when there’s maintenance work done.”

Anita Saxton, 39, and her son Nolan, 12, of Scottville, Mich., were killed in the accident Saturday.