The Mode S Beacon Replacement System Program

The FAA is safely integrating new types of technology into the National Airspace System, or NAS, while rebalancing existing services and modernizing our infrastructure to enable reduced costs and increased efficiency. The Mode Select Beacon Replacement System, or MSBRS, program supports that effort while providing safe and efficient air navigation services as part of the Air Traffic Organization, or ATO, mission. 

The main objective of the MSBRS program is to update outdated and unsustainable components of the current Mode Select, or Mode S, radar system. The legacy Mode S systems are more than 25 years old and suffer from a shortage of replacement parts and repair capabilities. MSBRS program goals include a new design that integrates contemporary surveillance interfaces, safeguards against cyber security risks, and includes necessary modifications to maintain the system's support and longevity. The program will replace rather than refurbish the legacy systems below the rotary joint. Additionally, the MSBRS initiative provides the opportunity to replace additional cooperative surveillance radar systems, such as the Air Traffic Control Beacon Interrogator Model 5, or ATCBI-5, and the Model 6, or ATCBI-6, thus improving overall cooperative radar service availability. 

Ground-based cooperative radar systems, such as Mode S, continue to be required for air traffic surveillance for the FAA to:

  • Detect aircraft not transmitting Automatic Dependent Surveillance-Broadcast, or ADS-B, due to improperly installed avionics, transponder failure, or non-equipped ADS-B aircraft
  • Complement ADS-B surveillance coverage areas (in rule and non-rule airspace)
  • Provide surveillance back-up service to ADS-B as needed for service resilience and safety

Cooperative surveillance radar systems identify and track transponder-equipped aircraft in en-route and terminal airspaces. The systems provide aircraft position and altitude information to air traffic control automation systems that is critical for maintaining safe and efficient flight operations for the flying public. The NAS currently has four different types of cooperative surveillance radar systems deployed as a backup to ADS-B. These include the following:

  • Mode S Beacon System Sensor – collocated with Airport Surveillance Radar Model 9, or ASR-9, ASR Model 8, or ASR-8, and Common Air Route Surveillance Radar, or CARSR, non-cooperative radar systems, and as a standalone Beacon Only System, or BOS.
  •  ATCBI-5 – collocated with ASR-9 and ASR-8 non-cooperative radar systems and as a standalone BOS.
  • ATCBI-6 – collocated with CARSR and Air Route Surveillance Radar Model 4, or ARSR-4, non-cooperative radar systems, and as a standalone BOS.
  • ASR Model 11, or ASR-11, Monopulse Secondary Surveillance Radar, or MSSR, collocated with ASR-11 non-cooperative radar systems.

Each of these cooperative surveillance radar systems have their own challenges and need long term sustainment or replacement. The MSBRS has been designated as a candidate to replace any cooperative surveillance radar system that is currently operational and provides an opportunity to consolidate the number of cooperative radars in the NAS.


The program is currently in the solution implementation phase of the FAA procurement cycle and aims to begin installing MSBRS units into the operational environment within the NAS at the end of calendar year 2025 or the beginning of calendar year 2026.

Program Components

  • Mode S
  • Air Traffic Control Beacon Interrogator Model 5 (ATCBI-5)
  • Air Traffic Control Beacon Interrogator Model 6 (ATCBI-6)

The quantity and timing of MSBRS procurements depend on:

The MSBRS program staff is actively engaged with the aviation industry. See the most recent Surveillance Service Industry Day presentations and the NAS Infrastructure Roadmaps for Surveillance Services for more information. 

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Last updated: Tuesday, January 9, 2024