A Spirit Airlines jet whose passengers said they heard an explosion and saw flames shortly after leaving Dallas/Fort Worth Airport sustained an especially serious type of engine failure, a National Transportation Safety Board official said today.The official told The Associated Press that it was an “uncontained” engine failure, meaning that broken pieces and parts of the engine escaped the outer engine housing. The official spoke on condition of anonymity because he is not authorized to speak publicly. The plane returned to the airport Tuesday afternoon and landed safely.Passenger Fred Edwards told WGCL-TV in Atlanta that he heard an explosion before flames came up the side of the plane, lighting up the interior of the Airbus A319. He and other passengers reported that smoke then filled the cabin.“The plane started shaking violently, and after that, the plane started filling up with smoke,” Edwards said.Spirit spokeswoman Misty Pinson said no injuries were reported. She said the captain received an indication of a “possible mechanical issue” shortly after takeoff from DFW at 1:37 p.m. She said by email Wednesday that there was no fire, before adding later that Spirit is “actively investigating to confirm the specifics of what happened and the cause.” The passengers were placed on another Spirit jet for Atlanta later Tuesday.Aircraft engines are designed to contain any broken pieces within the engine during a failure. That’s because when parts are released, they often spray like shrapnel and severely severe damage fuel lines, electrical cables, hydraulic lines and other crucial aircraft systems. Airliners can safely fly with only one engine if the other engine breaks down or has to be shut off, but damage from an uncontained engine failure can jeopardize the plane.Despite the government shutdown, the safety board is recalling furloughed investigators to open an inquiry into the incident, the agency official said.Federal Aviation Administration spokeswoman Laura Brown confirmed that the agency is investigating the incident as well. Spirit has grown quickly at DFW since it launched service in North Texas two years ago. The no-frills carrier, based in Miramar, Fla., is No. 2 at the airport behind American Airlines in terms of destinations, flying to 26 cities. But it is not the second-biggest in terms of capacity, because it mostly operates one or two daily flights on each route. Spirit is known for low fares but a bevy of fees that make passengers pay for everything from carry-on bags to water. This report includes material from the Star-Telegram archives.