A flight planning system for obtaining flight plans and/or weather information is provided with a portable computer having a display unit, keyboard, memory, built in modem and a built in disk drive that can be connected via telephone lines to a ground based data center. The basic flight planning data and/or weather request data is input in response to menu driven prompts and reviewed on the display by the pilot. The portable computer is then connected to the data center which generates a series of optimized flight plans and provides desired weather information. After the desired flight plan and/or weather information has been selected by the pilot, it is loaded onto a floppy disk in the disk drive. The aircraft is provided with a data transfer unit which accepts the floppy disk and downloads the flight plan and requested weather information into the onboard computerized navigation system. In addition the aircraft is provided with a VHF radio system for inflight communication with the data center so that the flight plan and/or weather information can be updated.