Traffic Alert/Collision Avoidance System (TCAS)

For the last 20 years, the Traffic Alert and Collision Avoidance System (TCAS) has had extraordinary success in reducing the risk of mid-air collisions. TCAS assists pilots in visually identifying nearby traffic, directly alerts pilots that a collision with another aircraft is imminent, and provides guidance to climb or descend to avoid a potential collision (see video below). Now mandated worldwide on all large transport aircraft and voluntarily installed on many business jet aircraft, TCAS is continuing to evolve in response to monitoring feedback and to existing and anticipated airspace changes.

Video example of a TCAS encounter.
Download Video: Closed Format: "MP4" Open Format: "OGG"


Lincoln Laboratory’s involvement in TCAS dates back to 1974, when the FAA tasked Lincoln to develop the surveillance subsystem and the MITRE Corporation to develop the collision avoidance algorithms. In addition to surveillance development, in the mid-1970s Lincoln began TCAS-related monitoring of aircraft in the Boston airspace, using a Lincoln-developed prototype Mode S sensor. In the mid-1990s, Lincoln was tasked with analyzing the performance of the TCAS threat logic, and began developing simulation and analysis tools to perform specific types of threat logic assessment in cooperation with the FAA William J. Hughes Technical Center. Since the early 2000’s, Lincoln has supported safety assessment and evaluation of proposed changes to the TCAS algorithms.

The Lincoln Laboratory Mode S Experimental Facility monitors TCAS performance.

Lincoln currently supports four major activities related to evaluation and development of current and future collision avoidance systems– TCAS monitoring, surveillance performance, 1030/1090 spectrum use, and future collision avoidance logic.  The Lincoln TCAS monitoring program has been adopted by the FAA nationwide to characterize TCAS performance and proactively identify issues to be resolved by modifications to current systems and/or development of future systems.  This nationwide monitoring data also supports analysis and simulation of current TCAS surveillance performance in light of changes in the air traffic environment occurring since development of the original surveillance logic.  To evaluate TCAS use of the 1030/1090 spectrum, TCAS-TCAS coordination, and to explore the potential applicability of ADS‑B data for collision avoidance use, Lincoln is performing 1030/1090 monitoring in the Boston area.  Finally, Lincoln is developing a new approach to collision avoidance logic that builds on recent advances in mathematics and computational resources.  This approach may facilitate adaptation to various airspace environments, as well as variations in aircraft and surveillance performance.

Major accomplishments

  • Lincoln developed metrics and analysis techniques which facilitated understanding of the safety impact and the cost/benefit of proposed TCAS changes.
  • Lincoln monitored and analyzed TCAS performance in the Boston airspace and is lead for expansion of monitoring and analysis of TCAS performance across the US.
  • Lincoln developed a state-of-the-art TCAS logic simulation and airspace model, making use of the Lincoln Laboratory parallel computing facility, LLGrid, to assess the current and proposed logic in a statistically robust manner.
  • Lincoln created the surveillance simulation capability which is critical to validating and understanding the performance of TCAS surveillance logic and understanding factors that influence surveillance performance.
  • Lincoln has completed initial development and validation of a new approach to collision avoidance logic that may allow for improved, more flexible collision avoidance performance.
top of page