The mystery of why two people failed to exit a burning school bus last December in Pottawattamie County, Iowa may never be solved, because the equipment that videotaped the bus’ interior was severely damaged by the fire.

That limitation will not stop the National Transportation Safety Board (NTSB) from forging ahead with its investigation into the early morning Dec. 12, 2017 incident that killed the 74-year-old driver and a 16-year-old student.

According to the NTSB, the tragedy began when the driver turned right into a driveway and picked up his first passenger.

How it happened

As the bus backed out of the driveway, its right rear tandem wheels crossed a 3-foot-wide earthen strip adjacent to the roadway and dropped into a 3-foot-deep ditch. Although still in contact with the ground, the right rear drive wheels lost traction, and the bus became stuck with about half of the vehicle positioned across the gravel roadway.

The driver attempted to move the bus forward out of the ditch. As he was doing so, a fire began in the engine compartment and spread into the passenger compartment. Sometime during this event, the grass and vegetation at the rear of the school bus also caught fire.

(Image source: Pottawattamie County Sheriff’s Office)

Why didn't they get out?

“For unknown reasons, the driver and student passenger did not exit the school bus,” says the NTSB. Both occupants died as a result of the fire.

The school bus, which was owned and operated by the Riverside Community School District, went into service in 2005. NTSB investigators found that the vehicle had been subject to three recalls that had all been performed. They involved a sensor used in the antilock brake system;  a sensor used in the side-mounted swing-out stop arm and the wiring harness to the stepwell heater blower motor.

No recoverable data

The school bus was equipped with a continuous onboard video recording system, manufactured by REI. The recording system was severely damaged by the fire, and the NTSB Recorders Laboratory determined that there were no recoverable data.

The NTSB plans to conduct additional examinations of vehicle components and post-fire evidence in order to determine the potential origin of the fire and its propagation. Vehicle inspection requirements, maintenance record requirements, and oversight of school bus operations will also be addressed, as well as human performance and survival factors issues related to the crash and fire.

“All aspects of the crash remain under investigation to determine the probable cause.”