A Seattle duck boat that swerved into an oncoming charter bus, killing five people and injuring dozens, did not have an axle repair that was recommended for at least some of the amphibious tour vehicles in 2013, federal investigators said.

Ride the Ducks International, which refurbished the vehicle in 2005, warned its customers two years ago about potential axle failure and recommended a specific repair or increased monitoring, National Transportation Safety Board member Earl Weener said at a Sunday news conference.

"This particular duck had not had the fix," he said of the former military landing craft repurposed as a tour vehicle.

Witnesses described seeing the duck boat’s left front tire lock up Thursday before it veered into the bus on a bridge. Federal investigators said they found the duck boat’s left front axle sheared off — though they said it wasn’t clear if the axle had broken before or after the crash. Investigators say it could take months to determine an exact cause of the crash.

Ride the Ducks International told investigators late Saturday about the warning, Weener said. It’s unclear if the company that owns the vehicle — Ride the Ducks of Seattle — was aware of it, he said.

"We’re going to be following that," Weener said.

Ride the Ducks of Seattle owner Brian Tracey did not say in a statement Sunday night whether the company knew of the warning.

"We are working to understand what happened and have completely opened our operations to NTSB investigators," he said.

Tracey said he was in "complete agreement" with calls by Gov. Jay Inslee and Seattle Mayor Ed Murray to keep the duck boats off the streets pending a state inspection of all the vehicles.

Four international college students died at the scene of the crash, and a fifth — identified as a 20-year-old woman — died Sunday, Harborview Medical Center said. They were among about 45 students and staff from North Seattle College who were on the bus when the tourist-carrying duck boat swerved into it on the six-lane Aurora Bridge with no median.

More than 50 people were taken to hospitals. At least 13 people remained hospitalized Sunday.

The amphibious vehicle tours operate around the world, including in Philadelphia; Austin, Texas; Miami; Fort Lauderdale, Florida; and London. The vehicle involved in the Seattle crash was an Army surplus craft built in 1945. It was refurbished with a General Motors engine and chassis in 2005, Weener said.

The NTSB had few details Sunday about the warning Ride the Ducks International issued. It wasn’t clear what prompted it, how the potential failure was discovered or whether it applied to all duck boats or only those that the company had refurbished, Weener said.

It wasn’t clear how many of the 100 duck boats in service nationally may have had the repair, he said.

The warning included specific instructions for inspecting the area where the shaft could fail as well as instructions for the repair, which involved welding collars around the axle shaft, Weener said.

Results of the federal investigation are not expected for a year, he said. Investigators have interviewed 11 surviving passengers, including eight who were on the duck boat, as well as first responders. They expect to interview the drivers of the charter bus and the amphibious vehicle this week.

Weener said Ride the Ducks of Seattle has been cooperative and had turned over training records and maintenance documents for the vehicle involved in the crash.

State regulators also have opened an investigation, which entails inspecting all vehicle and driver records.

The vehicle in the crash underwent regular annual examinations by a federally certified inspector, most recently in 2015 and 2014, and met federal standards, said Amanda Maxwell, spokeswoman for the Washington Utilities and Transportation Commission.

(Copyright (c) 2015 The Associated Press. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)

Join our Newsletter for the latest news right to your inbox