Help with an acceleration mission

Could someone kindly tell me how to change from the helicopter to the DC 3 in the "save the rhino" mission. I've the landed the copter in the little helipad and the copilot tells me to get in the DC3 and fly it to the next airport, except I cant get out of the copter and into the goonie!!
I cant find a command anywhere. Or is there maybe something wrong with the program? Thanks in advance, bigfoot.
