Rollback

A rollback occurs when a launched coaster does not generate enough speed to crest the highest point of the circuit and instead rolls backward under gravity to the launch position. On hydraulic launch coasters — the technology used by Intamin on Kingda Ka, Top Thrill Dragster, and Stealth at Thorpe Park — rollbacks happen when the hydraulic launch mechanism fails to deliver its full specified power. The train rolls back slowly and is caught by magnetic brakes at the bottom of the launch track.

Passengers are not harmed during a rollback — the catch brake system is designed specifically for this scenario — but the ride is interrupted and guests must either wait for a re-launch or disembark. Rollbacks are a known characteristic of hydraulic launch coasters and occur with some regularity at parks that operate this technology. For many enthusiasts, experiencing a rollback — and the unexpectedly gentle backward drift after the failed launch — is itself a memorable event worth noting in their park diary.