Airline's chief says it must "unlock new sources of revenue" after profits tumbled almost 50% in last quarter.

US aviation authorities are investigating the incident which happened outside Oklahoma City.

The Southwest Airlines flight had to return to Denver International airport shortly after taking off.

The penalty is the heftiest issued on an airline following the delays last winter for two million people.

Eyewitness video shows flames near the engine of the Boeing 737 shortly after take-off.

They are told to attend after a judge said Southwest Airlines disregarded his order in a free speech case.

The cabin filled with smoke after take-off which sparked panic on the US-bound flight from Cuba.

It comes less than a month after a similar close call between two passenger planes in New York.