All safety benefits to be derived from the Traffic Alert and Collision Avoidance System (TCAS) are dependent upon the aircraft crew understanding and reacting appropriately to the TCAS advisories. For this reason it is important to display the TCAS information so that it can be promptly and unambiguously understood by the crew. It is also important that the crew be able to integrate the TCAS advisory information with information from other sources so that TCAS becomes a compatible addition to pre-existing safety procedures and not a contending alternative. Because crew response to TCAS is strongly influenced by visual cues received from outside the cockpit, testing in actual flight has proven important. Under sponsorship of the Federal Aviation Agency (FAA), Lincoln Laboratory conducted a series of flight tests with an experimental TCAS II unit to investigate crew response issues.