INCIDENTS involving two Duck amphibious passenger vehicles in which one sank and the other caught fire highlighted extremely poor maintenance and a failure to meet standards, an accident investigation chief has said.

It was "extremely fortunate" that none of the 33 passengers and crew on board the Duck vehicle Wacker Quaker 1, formally known as a DUKW, were drowned or injured when it sank in Salthouse Dock in Liverpool on June 15 2013, said the Marine Accident Investigation Branch (MAIB) chief inspector Steve Clinch.

In the second incident, when the London-based Duck Cleopatra caught fire on the River Thames in London on September 29 2013, the 28 passengers and two crew had to take to the water and were rescued by other vessels without serious injury.

The Wacker Quaker 1, whose passengers either swam ashore or were recovered by other crafts' crews, was the second Duck vehicle to sink in Salthouse Dock in a three-month period.

The MAIB report said that on both occasions the Ducks did not have the quantity of buoyancy foam required to provide the mandated level of residual buoyancy.

Mr Clinch said that it became clear that other DUKWs operating in the UK also did not have the quantities of foam required and that focus had shifted to ensuring that these amphibious passenger vehicles would float when flooded.

The Cleopatra's operators, London Duck Tours, made buoyancy amendments. But Mr Clinch explained that in the case of Cleopatra the "foam was so tightly packed around machinery that it caught fire, resulting in 30 passengers and crew needing to rapidly abandon the vehicle into the Thames".

The MAIB said that in the June 2013 Liverpool incident the passengers and crew were not adequately prepared to deal with the emergency situation. Also, the Maritime and Coastguard Agency's (MCA) periodic survey and inspection regimes, and their unscheduled interventions had been ineffective.

Mr Clinch said: "This has been a protracted investigation during which it has become evident that regulators in several countries have struggled with the challenge of certifying World War 2 DUKWs for commercial passenger-carrying operations.

"The sinking of two Liverpool DUKWs in quick succession highlighted extremely poor standards of maintenance, and that for nearly 14 years they had operated with insufficient buoyancy foam to keep them afloat should they suffer major damage.

"It was extremely fortunate when DUKW Wacker Quacker 1 sank in Salthouse Dock that none of the 33 passengers and crew on board were drowned or injured as they abandoned ship."

He went on: "I am encouraged that the MCA and DUKW operators are working closely together to devise a framework for safely operating amphibious vehicles in the future.

"However, I am concerned that it has required two potentially fatal DUKW accidents to stimulate all involved into taking actions that should have been completed before passenger carrying operations were first authorised."

The report said that Liverpool Duck operators The Yellow Duck Marine was no longer operating, while London Duck Tours had made various amendments.