TCAS I provides pilot information on the position of nearby aircraft as aid to see and avoid. TCAS I also issues traffic alerts on aircraft that may be a collision threat. This includes traffic advisory information indicating the range, bearing, and altitude of nearby aircraft. This information is obviously useful to visually acquire intruders and maintain separation. TCAS II provides the information of TCAS I and also provides resolution advisories in the vertical plane of the aircraft. The system analyzes the projected flight path of approaching aircraft and indicates maneuvers such as CLIMB for collision avoidance. ACAS will ultimately be implemented in place of TCAS to decrease the risk of mid-air collisions. ACAS is based on the RTCA TCAS standard which includes the Change 7 logic. This change includes more than 300 detailed modifications to the surveillance and collision avoidance algorithms and displays in TCAS equipment. These changes were deemed necessary by the industry and users for continued safe operation of TCAS. Some of these changes include vertical tracking of threats by using altitude data quantified to 25 ft. when available for Mode S equipped aircraft. Resolution advisories issued for vertically converging aircraft will now usually call for a level off rather than a reversal of rate or action. Radio altitude input information will be used more accurately to prevent TCAS from issuing inappropriate command at low altitudes TCAD is a traffic avoidance system produced by Ryan International. Although it does perform some similar functions as TCAS, it is not currently an acceptable system to meet the current TCAS requirements for commercial aircraft.