Federal investigators have released some details in the investigation into a plane that caught fire on the tarmac of Denver International Airport after making an emergency landing in March. The preliminary report from the National Transportation Safety Board shows that when investigators examined the right engine, they found some issues. 

According to the NTSB, investigators found a broken fan blade and the lockwire of a fuel fitting installed in the wrong direction. 

American Airlines Flight 1006 plane carrying 178 people, caught fire on the tarmac after making an emergency landing at Denver's airport on March 13. The incident involving the Boeing 737-800 sent 12 people to hospitals, but all injuries were minor.

The flight had departed from Colorado Springs Airport and was bound for Dallas-Fort Worth International Airport when the "crew reported engine vibrations."  

Some passengers were able to take the ramp into the concourse. Others used an evacuation slide from the rear of the plane, where the smoke was stronger. Passengers also evacuated onto the wing on the opposite side of the plane from the fire.  

The NTSB expects a final report on the incident within 12-24 months.