"And more importantly, they want to make sure that no one ever dies again inside a death trap, duck boat", said attorney Robert Mongeluzzi.
The duck boat that capsized during a storm in southwestern Missouri, which left 17 people dead, was raised to the surface of Table Rock Lake on Monday in an effort overseen by the Coast Guard.
Seventeen of the 31 people on board died, including nine members of a family from Indianapolis.
Word of the investigation comes days after the filing of a wrongful death lawsuit seeking $100 million in damages from the operator of the duck boat.
He said it's unlikely duck boat operators in Branson were surprised by stormy weather July 19 because a severe thunderstorm warning was issued around 6:30 p.m. local time. The lawsuit was filed Sunday on behalf of 76-year-old Ervin Coleman and 2-year-old Maxwell Coleman Ly, two of the nine members of an in family who died in the incident.
He said duck boats' canopies trap people when the boats sink and the duck boat industry was warned about that hazard more than a decade and a half ago.
When the boat sank, the lawsuit contends it was the culmination of defective design, ignored safety and storm warnings and breaks in company protocol.
"We remain deeply saddened by the tragic accident that occurred in Branson and we are supportive of the affected families".
The NTSB investigation is focused on when operators of the duck boat chose to take the vessel into the water and when they became aware of a severe thunderstorm warning, a source with knowledge of the investigation has said.More news: Why Prince Harry and Meghan Markle Are Disregarding These Royal Rules
Mongeluzzi said canopy coverings on the duck boats make it hard for passengers to escape the vehicle in the event of an emergency.
Dozens of people have been killed in multiple accidents involving duck boats over the past 20 years. Last year, Ripley Entertainment acquired the Ride the Ducks attraction in Branson.
The lawsuit also alleges that during a safety briefing, passengers were told they would not need their life jackets.
The Indiana family's suits allege that the companies ignored warnings the National Transportation Safety Board in 2000 that the vehicles, which are created to operate on land and water, should be upgraded to ensure they remain upright and floating in bad weather.
But the NTSB, which issued its preliminary findings on Friday, said, "as such, no conclusions regarding the cause of the accident should be made from this preliminary information".
On Monday, another suit was filed by the family of William and Janice Bright of Higginsville, Missouri, a couple who was also killed in the July 19 incident.
When the waves swelled beyond 2.5 feet, the captain should have instructed passengers to put on life jackets, but allegedly did not. The estates of two other Coleman family member were named in an earlier filing.
According to the lawsuit, Ripley's hired an individual to inspect the duck boats prior to their purchase in December of 2017. Mongeluzzi said. "I've been asked 'You've said duck boats should be banned, what about the effect on tourism?' The Branson duck boats are owned by Ripley's, and, believe it or not, you don't promote tourism by killing tourists". The federal suit says 42 deaths have been associated with duck boats since 1999.
At 7 p.m., according to the NTSB, "whitecaps rapidly appeared on the water and winds increased".