CRJ200 flight crew departed with preliminary weight and balance numbers; discovering the error during preparation for landing. Each pilot had assumed that the other had entered final numbers during maintenance distractions at departure time.

Narrative

Just prior to departure; Captain entered the planned performance numbers into the ACARS performance page and got the preliminary takeoff data numbers. At this time; Maintenance came into the cockpit to sign off a last minute problem. This caused a distraction to the flight crew who was concerned with the approaching departure time. The mechanic left the cockpit; the door was closed and we pushed on time. Unfortunately; the First Officer saw the numbers and assumed that the Captain had set the actual takeoff data. The Captain; at the same time saw the numbers set into the Vspeed fields and assumed that the First Officer had finished what had been started. Neither was correct and the flight departed with the preliminary speeds set instead of the actual data. The flight continued to destination uneventfully. The crew realized that the error had occurred when they went to get the landing numbers. Since the ACARS had not been properly set to begin with; these numbers where unavailable. The crew made use of the Vspeed cards and some mental math and deduced an approximate landing weight. The flight landed uneventfully.