The Graphical Weather Service (GWS) is a data link application that will provide near-real-time graphical weather information to pilots in flight. To assess the effect GWS, as well as to aid in the proper design, implementation and certification of the use of GWS in aircraft, two human factors studies have been conducted. The second study conducted (Phase Two) is the topic of this report. Phase Two was conducted to determine the maximum level of compression-induced distortion that would be acceptable for transmission of weather images to the cockpit. To make this determination the following data were collected and analyzed: pilot subjective ratings of the perceived amount of distortion of a compressed image, pilot subjective ratings of the acceptability of a compressed image for use in the flight task, and pilot route selections as a function of the amount of compression presented in an image. Results indicated that images of low to moderate compression levels were generally acceptable for transmission to the cockpit, while images that were highly compressed were generally unacceptable. In addition, computed measures of image quality have been identified to enable the establishment of a criteria for transmitting images to aircraft.