VALLEJO (CBS SF) — Six Flags Discovery Kingdom on Monday is investigating what caused a malfunction on one of its roller coasters that left a dozen riders stuck 15 stories in the air on Sunday.

The Vallejo Fire Department responded shortly before 3 p.m. to the Superman Ultimate Flight roller coaster.

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Vallejo fire spokesman Mark Libby said Monday that a two-person rescue team was raised 150 feet in the air on a mobile platform to reach the jammed roller coaster.

The rescue team had the option of removing the passengers from the ride or trying to get the ride moving again, Libby said.

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They chose the latter approach and shook the cars, which dislodged the coaster from where it was stuck and allowed it to move forward again on the track, he said.

The riders were able to get off the ride safely and no injuries were reported.

The rescue team conducted training on the Superman ride before it opened in June in order to prepare for an incident like Sunday’s, Libby said.

This is not the first time a ride at Six Flags in Vallejo has malfunctioned. In August 2010, a problem on the Boomerang Coast to Coaster left 26 passengers stranded for an hour.

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