Riders hang over the Strip on the Stratosphere's X Scream thrill ride on Oct. 31. A power outage Tuesday night left six tourists stranded. Photo by John Gurzinski.

There will be no X Scream activity at the Stratosphere until safety inspectors examine the circumstances that left six tourists stranded on the world's third highest thrill ride during a power outage Tuesday night.

Las Vegas inspectors shut the ride down early Wednesday morning, said Paul Wilkins, Las Vegas director of building and safety.

Recreation Engineering Inc., which specializes in amusement ride safety issues, has been asked to conduct the investigation, which began late Wednesday afternoon.

"Right now, we are conducting a thorough and complete investigation," Stratosphere spokesman Mike Gilmartin said. "We won't have any comment until it's complete."

The X Scream incident is the second time this year that tourists have been left hanging by a thrill ride at the Stratosphere. In April, two cousins were stuck on the Insanity ride for about 80 minutes when high winds triggered a safety feature that caused a shutdown.

"For whatever reason, we've now had two retrieval operations that malfunctioned in a row," Wilkins said. "...I really want someone to do a test on this and find out why."

The X Scream ride abruptly halted about 5:45 p.m. when the resort went dark after power and telephone lines became somehow entangled, officials said.

Visitors from Japan were aboard the ride, which is shaped like a giant teeter-totter, moves riders 27 feet over the edge of the Stratosphere observation deck, 866 feet above the Strip.

The tourists were stuck in that position in the chilly night winds for about 90 minutes before workers were able to return them to the platform. At least five of the tourists were taken to UMC to be checked out after they were rescued.

When the outage occurred, Gilmartin said, employees first secured the ride with straps and cables to safeguard passengers. What followed is what inspectors will review. The X Scream has an emergency retrieval system that is supposed to allow workers to return it to the observation deck manually. That system either malfunctioned or was not used before the power came back on.

Wilkins said that in the past, the Stratosphere has complied with requirements for regular inspections and maintenance of ride features. His concern centers on the retrieval systems, which either were not used or did not work properly. Wilkins said that while the trapped passengers may have been frightened, he believes they were safe.

"There are no doubts in my mind about the structural stability of the rides," Wilkins said.

Kathy Fackler, president and founder of Saferparks, a California-based non-profit group that lobbies for amusement ride safety, said she was pleased that no one was hurt in the incident.

She also said Clark County and Las Vegas have strong regulations in place to secure rider safety. If a problem exists, Fackler said it will be identified.

"That's the good news. I feel there's a good, strong technical oversight program in place."