In Chicago, pilots were forced to abort a takeoff and evacuate passengers from a burning American Airlines flight on a runway at O’Hare International Airport.

On Friday, a federal official says the airliner experienced an “uncontained engine failure” a rare and serious type of failure that happens when engine parts break off and are spewed outside the engine.

Flames and heavy black smoke poured from the side of Miami-bound flight as it sat on the runway.

Officials say the incident left 21 people injured.

The National Transportation Safety Board will conduct an investigation into the incident.