Mechanical failure caused the fatal Ride the Ducks Seattle crash in 2015. The National Transportation Safety Board issued that formal ruling Tuesday.
The NTSB ruled the left axle housing on the Ride the Ducks amphibious tour vehicle broke. That caused it to veer into a tour bus filled with international students. Five students died, and 69 other people were injured in the crash on the Aurora Bridge.
The NTSB says workers performed inadequate repairs on that axle 10 years earlier. NTSB chair Christopher Hart also says the vehicles, known as APV's, have operated nationwide without any federal oversight.
Hart: "A tourist who travels on a commercial vehicle enjoys many safety protections. Upon boarding the APV however, those protections are lost. We also saw that these loopholes can have tragic effects on occupants of any other vehicles that happen to be nearby."
The National Transportation Safety Board has issued an urgent recommendation that the company stop using the vehicles until their axle housings are completely repaired. The board also wants the company to install seatbelts, and require passengers to wear them while the vehicles travel on land.
Another recommendation: that tour guides, not drivers, conduct the tour.
In a statement, Ride the Ducks Seattle said it has voluntarily taken many of the steps the transportation board recommended, and is working to become the safest commercial fleet in operation.