NTSB Chair Jennifer Homendy told reporters after a Senate hearing the airplane had been in for maintenance the night before the incident in which it lost the engine cowling.

The board opted not to open a formal investigation, Homendy added.

Southwest Flight 3695 returned safely to Denver International airport around 8:15 a.m. local time on Sunday and was towed to the gate.

(Reporting by David Shepardson; Editing by Chris Reese)