Communications datalink, the transmission of messages as screen-displayed text between cockpits and ground stations, appears to offer both advantages and disadvantages compared to conventional VHF voice communications. The study reported here examines both the communication and performance of integrated communications datalink in single pilot instrument flight operations. Sixteen pilots flew two cross-country instrument flights in an AST complex-aircraft flight simulator with a moving map, traffic, and datalinked message display. In the conventional voice condition experimenters played the role of ATC controllers speaking over the radio. In the datalinked condition, controllers operated a computerized ‘ground station’, sending and receiving text messages on screen. Pilot communications, control and performance data were monitored for each phase of flight, as well as the interaction of pilot expertise and workload. The results suggest that communications datalink may widen the performance gap between experienced and inexperienced aviators, and that delayed responses are such that operational difficulties could occur, not least in busy airspace.