MARYVILLE, Tenn. — A single bolt caused a rear axle to fall off a school bus as it was driving away from a school last week, WBIR reports.

Sharon Anglim the director of communications and special projects for Maryville City Schools, told WATE that the bus left the pickup line on the afternoon of Dec. 2, and stopped in front of Maryville High School when both of the back wheels and axle broke away from the bus. She added that no students were hurt.

Authorities said that the “ti bolt” that connects the vehicle springs was broken, according to WBIR. Sgt. Randall Martin with the Tennessee Highway Patrol told 10News that the bolt breaking started a chain reaction that led to the axle falling off the bus.

The Tennessee Highway Patrol inspects school buses at least once a year, and state law requires the buses to be inspected twice a year. The bus was inspected in April and October, and had passed both inspections, according to WBIR. Martin also told the news source that although inspectors review pieces of the bus to ensure they are intact, they do not take components apart, and that the broken bolt could not be seen during a routine inspection.

Brad Long, the owner of the bus, told WBIR that the whole rear end of the bus would have to be taken off to see the bolt. Martin added that to prevent this from happening again, a good maintenance program with mechanics who check for potential problems that troopers can’t is needed. Long also said that he is having several other buses inspected to check for similar problems, according to the news source.