SEATTLE (AP) — After hearing reports from the NTSB staff who investigated the deadly Ride the Ducks crash in Seattle, the board determined the probable cause was a mechanical failure and improper maintenance of the amphibious passenger vehicle.

NTSB Chairman Christopher Hart also said Tuesday contributing factors to the severity of the 2015 crash that killed five and injured 69 people was a lack of protections for the passengers, including seatbelts.

Hart said "APVs, or 'Duck Boats,' provide a unique sightseeing option in many American cities, yet until now, these vehicles have been operated without any regulatory oversight when driven on our roads and highways."

The board issued 10 new safety recommendations that include requiring the use of seatbelts when the vehicles are on the road.

The board issued one urgent recommendation that requires Ride the Ducks International to order all of its franchise companies to stop using the stretch vehicles until their axle housings can be repaired or replaced.

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