This document sets forth functional, procedural, and design criteria and recommendations concerning human engineering of data link systems. recommendations are based on limited evidence from empirical and analytic studies of simulated data link communication, and on experience from operational tests and actual use of data link. However, because data are not yet available to support recommendations on all potentially critical human engineering issues these recommendations necessarily go beyond the data link research and include requirements based on related research and human factors engineering practice. It is also recognized that evolution of these recommendations will be appropriate as experience with data link accumulates and new applications are implemented.