The National Transportation Safety Board (NTSB) sent a six-member team to investigate Friday’s motorcoach accident in Arizona that killed seven and injured 14 more passengers.

The single-vehicle bus crash occurred Friday on a straight stretch of U.S. 93, about 70 miles southeast of Las Vegas. The motorcoach, which was carrying 24 passengers who were returning from a trip that had left Las Vegas for the Grand Canyon earlier that day, veered right and then left across the median, rolling at least once before resting across the southbound lanes of the highway.

After inspecting the crash site, the investigators planned to head south to Kingman to evaluate the bus, according to AP reports.

The investigation is expected to take between 12 to 18 months, with Senior Highway Safety Investigator Pete Kotowski serving as the Investigator-in-Charge.