Riding a roller coaster is supposed to be thrilling, but it’s not supposed to involve actual danger. Unfortunately, one Six Flags ride in Maryland’s Prince George’s County has been proven fallible twice. In the latest incident, at about 5:45 p.m. Eastern on Thursday, 24 people got stuck on the top of the enormous coaster. As of 7 p.m., they’re still up there, and a rescue mission is underway.

Joker’s Jinx, located in the Gotham area of the park, is one of the most popular attractions at Six Flag America (the one that serves the Washington, D.C./Baltimore area). It’s a quick ride, filled with rapid twists and turns, and is over ten stories high. Folks on the ground at the park estimate that the riders are stuck 100 feet in the air at an approximately 20-30 degree angle. It’s lucky that the car didn’t stop in the middle of one of the ride’s several upside down segments.

A gigantic ladder is being used to recover the riders. The rescuers are moving slowly: securing the system, putting the riders into harnesses, and bringing them down the ladder one by one. The mission is expected to take several hours — night will have fallen by the time it’s finished — but they want to take their time to make sure that no one gets hurt on the way down.

Six Flags doesn’t yet know what caused the ride to get stuck, though they will later conduct an investigation. It is unlikely to be an operator error, as the role of operators in administering the ride is limited to pushing a single button at the start.

A similar incident occurred on Joker’s Jinx in this same exact park in August 2014. That debacle also affected two dozen people, who were stuck around 80 feet in the air and were fully rescued after about four hours. The weather was extremely hot that day, so members of the Six Flag crew used umbrellas to shield them from the sun. The riders who are currently stuck on the ride are unfortunately at a segment that is inaccessible to ride operators; luckily, the weather in P.G. County is pleasant and dry today, with light winds and a temperature in the upper 60s.

Check out a live feed of the rescue mission from NBC Washington.

These folks should be back on the ground in a few hours.

P.G. County’s Six Flags park just opened yesterday for the spring season. What a beginning. Check out what the ride is supposed to be like in the video below.

Photos via Photo via Six Flags / Duane Marden / rcdb