After takeoff, Cooper told Mucklow to join the rest of the crew in the cockpit and remain there with the door closed. As she complied, Mucklow observed Cooper tying something, possibly the money bag, around his waist. At approximately 8:00 p.m., a warning light flashed in the cockpit, indicating that the aft airstair apparatus had been activated. Rataczak offered assistance via the aircraft's intercom system. Cooper refused. This was the last communication they had with him. The crew soon noticed a subjective change of air pressure, indicating that the aft door was open.