The Firebird roller coaster came to a “controlled stop at the top of the lift hill” just after 6 p.m., Six Flags officials said in a statement, according to FOX 5 D.C.
All of the passengers were safely removed from the ride by 9 p.m.
The Firebird opened in May, replacing another roller coaster that closed last year.
The ride takes “thrill-seekers through incredible twists, drops and inversions, all while seated in state-of-the-art floorless trains,” according to the theme park’s website.
The ride will remain closed until certified ride technicians inspect it and clear it for operation, officials said, according to FOX 5.
It is the only floorless roller coaster in Maryland, the website says.