The National Transportation Safety Board has determined that a punctured tire caused the bus crash that killed 17 members of Houston’s Vietnamese Catholic Community last year.

The August 2008 accident happened when a charter bus carrying 55 passengers to a retreat in Missouri plunged over a highway bridge in Sherman, about 60 miles north of Dallas.

The safety board found that a retreaded tire on the vehicle’s right front axle became underinflated and failed. Federal regulations prohibit retreads from being affixed to the front of buses. However, the fact that the tire was a retread wasn’t cited as a cause of the blowout.

The board also found that the failure of the bridge’s railing and a lack of seat belts contributed to the wreck and its casualties.