WASHINGTON (AP) — Amtrak canceled all of its high-speed Acela Express service in the Northeast again after raising new concerns about a piece of equipment underneath the locomotives.

The decision was made after a more rigorous inspection of one train that had been cleared to return to service Thursday morning in the Boston-New York-Washington corridor, Amtrak spokesman Bill Schulz said.

"They found cracks that had not been previously detected," he said.

All 18 Acela Express trains, important moneymakers for Amtrak, were pulled from service Tuesday after inspectors discovered cracks in brackets that attach shock-absorbing "yaw damper assemblies" to the locomotives.

Thursday's decision represented the second cessation of all Acela trains this week.