The chairman of the National Transportation Safety Board says an investigation into a deadly amphibious tour boat crash in Seattle found it was caused by a mechanical failure. NTSB Chairman Christopher Hart said Tuesday the Ride the Ducks vehicle had a fractured left axle housing. Five people died and 69 people were injured in the Sept. 24, 2015, accident. Hart said in his opening statement at a meeting of the agency that the chain of events leading to the crash began years before it happened. He says there were missing layers of safety oversight in the way amphibious passenger vehicles were manufactured, operated and maintained.