The carrier did not alert passengers that they could leave the plane while it sat at the gate for a long period of time with the door open, the DOT said.
"Airlines may not leave passengers stranded indefinitely aboard an aircraft, whether on the tarmac or at the gate, and passengers have a right to know if they are able to leave the plane," said Transportation Secretary Anthony Foxx.
On March 21, Qantas' flight to Brisbane was scheduled to depart at 10:00 p.m. but returned to the gate three times after receiving mechanical alerts. The first time it returned to the gate, the plane sat there for over an hour and the second time the plane sat there for a little over two hours. The DOT says that during both of the delays the aircraft door was open and passengers could have deplaned. The flight ended up being cancelled with passengers disembarking the plane at 3:05 a.m.