The plane is making a sharp descent, but from the camera's POV, the scenes inside are still level.
They are flying a DC-3 from Geneva, Switzerland to Havana, Cuba a distance of 5,000 + miles. They make no mention of any stops. The DC-3 had a range of less than 1,600 miles and a max speed of 230 MPH. even if the plane had had enough range, the single pilot flying would have been at the controls for approximately 22 hours non-stop.