The 13 former employees sued the airline over the July 14, 2014 flight, which they say was preparing for takeoff at the San Francisco airport when workers discovered the six-inch-tall graffiti written on the tail about 30 feet off the ground.
In the wake of the disappearance of Malaysia Airlines Flight 370 four months earlier, Lam and the crew said they perceived the message as a serious threat.
But according to the 26-page complaint, United Airlines refused to deplane Flight 869, and the ground crew inspected only the auxiliary power unit, or APU, near the drawings, and said it was a "joke."
The flight attendants refused to fly without a full security sweep, and the trip that was was canceled since United had no crew.
Two months later, they were all fired for insubordination.