A paid passenger on an expedition to the Titanic with the company that owned the Titan submersible testified before a U.S. Coast Guard investigatory panel Friday that the mission he took part in was aborted due to an apparent mechanical failure.

The scientific director for the company that owned the Titan submersible that imploded last year while on its way to the Titanic wreckage testified that the sub had malfunctioned just prior to the fatal dive.