An engine caught fire on a United Airlines jet during takeoff Wednesday, forcing the evacuation of 102 passengers and five crew members, authorities said. Seven people were injured. The twin-engine Boeing 737 bound for Chicago was taxiing down a runway at Little Rock Regional Airport about 9:30 a.m. when the fire was spotted and the takeoff was aborted, United spokesman Charles Novak said. Airport firefighters doused the burning engine, he said. Many of the passengers, who exited through emergency door and window exits, jumped from the wing of the plane to the ground and were injured. Seven people were treated at hospitals, authorities said. Most of the passengers caught the next flight out to Chicago. Novak said airline officials had not determined what caused the fire. Investigators from the National Transportation Safety Board were at the airport late Wednesday to investigate the accident.