Data recovered from a ferry that sank off the coast of British Columbia seven years ago, killing two passengers, depict a routine voyage until the ship missed a scheduled turn and sailed into an island, a crew member's criminal negligence trial has heard.

On Tuesday, an expert witness took Karl Lilgert's trial through data recorded by the ship's electronic chart system, which the court heard is akin to the ferry's "black box."

Mr. Lilgert is charged with criminal negligence causing the deaths of two passengers, Gerald Foisy and Shirley Rosette, who have not been seen since the Queen of the North passenger ferry sank in the early hours of March 22, 2006.

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Lee Alexander, who teaches at the University of New Hampshire and is an expert in electronic marine navigation, was asked by the RCMP to analyze data from the ferry's electronic chart system.

Prof. Alexander reviewed that data numerous times. He said the only thing that appeared out of the ordinary during the sailing was a single, missed course alteration, which occurred shortly after midnight as the ferry entered Wright Sound after passing through a narrow strait known as Grenville Channel.

"As the vessel approached midnight, there should have been a turn. This did not occur and the vessel proceeded on a straight course to Gil Island."

The Crown has pointed to the chart system to support its claim that Mr. Lilgert failed in his duties as navigational officer when the ship missed the turn and sailed directly toward Gil Island. The Crown has told the jury the ferry took no evasive action before striking the island.

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Mr. Lilgert's lawyers have said the electronic system was frequently inaccurate, sometimes placing the ship's position high up on land as it sailed down the coast. They've said crew members referred to it as a "box of lies."