On June 2, 2003, approximately 1740 mountain daylight time, an Embraer, EMB-120ER, N299UX, operated by Great Lakes Aviation as flight 5120, was substantially damaged when it struck a ramp vehicle while taxiing to its gate at Denver International Airport (DEN), Denver, Colorado. The 2 airline transport pilots, 1 flight attendant, and 24 passengers were uninjured. The scheduled domestic flight was operating under Title 14 CFR Part 121 on an IFR flight plan. Visual meteorological conditions prevailed for the flight that originated in Dickinson, North Dakota, at approximately 1530. According to the pilot, he was "following the ramp agent's marshalling signals" while parking the airplane in Zone 4 at DEN. The pilot initiated a right turn as signaled and stopped when he lost sight of the ramp agent. The ramp agent had bent down to move a set of wheel chocks. The ramp agent "came back into [the pilot's] view after a few seconds and gave [him] the command to continue [his] right turn." Once the turn was initiated, it "became difficult to move [the airplane] without having to use more power than should be required." The pilot stopped the airplane and, upon exiting, discovered that the airplane had come in contact with one of the ramp vehicles." The tug operator stated he had observed the airplane stop and thought it was finished with the parking and ready for service. He positioned the tug and baggage cart behind the airplane to unload baggage. The airplane began to move again and he was unable to move the vehicle before the collision occurred. The ramp agent did not see the tug move in behind the airplane prior to re-initiating the turn. The airplane's right aft fuselage was crushed inward puncturing the aft cabin pressure bulkhead.