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Primus II Radio System

Primus II Radio System

Stay in touch with a versatile radio system to meet your needs.

Primus II Radio

Primus II radio system is a complete system featuring integrated navigation and communication, combined control and blended audio systems. The key benefits are:

  • Integrated communication unit
  • Integrated navigation unit and the associated antennas
  • Very high frequency communication
  • Air traffic control transponder capability
  • Mode A/C, S, and Mode S w/diversity
  • Elementary surveillance

ADS-B Mandate – Primus II Radio System Upgrade

The ADS-B Out Mandate requires 1090 Extended Squitter (ES) Mode S capabilities in 2020. The 1090 ES transmits your aircraft’s position, direction of flight, velocity, vertical climb / descent to air traffic control computers allowing controllers to track your position / path with greater accuracy.

If you’re flying an aircraft equipped with older, non-compliant Primus II radios, you can cost-effectively upgrade to new, fully compliant Primus II radios now.

Overview information about the ADS-B Out upgrading to the Primus II communications units RCZ-833XRCZ-851XRCZ-854X, the GPS/GNSSU, and radio management unit upgrade is included.

Primus II Communication Unit ADS-B Out Upgrade

Due to the large variety of Primus II configurations fielded, and to the variations found in the configurations, some units may require significant upgrades to reach the ADS-B configuration. Some of the fielded Transponders and Cluster Modules may not be upgradeable and will have to be replaced with a compliant new module. Contact your Honeywell representative or qualified service facility for specific information.

RM-855 Radio Management Unit Upgrade

The RM-855 Radio Management Unit (RMU) is mounted in the cockpit panel and is the primary interface used to control the radio system functions. The RMU software will need to be upgraded to either the -97X or -98X versions in order to provide the control, testing, and additional failure indications of the ADS-B Out functionality (ADS-B FAIL and ADS-B DGR). The RMU software upgrade will allow for additional communication to the RCZ cluster module on the radio system bus and display of the additional RCZ configuration straps in the maintenance pages.

Global Positioning System (GPS) Requirements

To be DO-260B ADS-B compliant, a GPS “Selective Availability Aware” (GPS SA) capable sensor (developed to TSO-C145b or TSO-C146b) must provide the position, velocity, altitude, figure of merit, and integrity limit data for the Mode S Transponder.

A Global Positioning System (GPS) upgrade is part of the ADS-B Out requirement. Honeywell’s GPS units provide highly accurate global positioning satellite navigation information for the full range of flight to meet the C-145b / -146b requirement. The upgraded GPS unit will retain Departure, Climb, En-route, Descent navigation and add the SBAS correction for required ADSB three-meter accuracy and the GPS-based LPV approach.

KGS-200 Global Positioning System / SBAS

The KGS-200 Mercury PX GNSS is a small, remote-mount 24-channel GPS receiver that includes Satellite Based Augmentation System (SBAS) capability. SBAS provides GPS position corrections that result in highly accurate lateral and vertical position information necessary for LPV approaches. There are various SBAS systems around the world and the GNSSU is compatible with all currently defined systems.

Global Positioning System Active Antenna/ SBAS

The GPS antenna will need to be replaced with one that meets DO-301 and TSO C-190. The new antenna shares the same fit characteristics as existing GPS antennas, it is just slightly taller.

Honeywell Global Navigation System Sensor Unit (GNSSU)

Compliance to the current Australian and EASA mandates may be achieved withHG2021GD02/GD03 GNSSUs, but for full compliance to DO-260A or B, upgrade to the HG2021GD06 or later, or replacement with a KGS-200 is recommended.

  • For aircraft equipped with Honeywell HG2021GD04 or HG2021GD06 GNSSU, there is no need to upgrade the GPS required as these GNSSUs meet the SA Aware requirement.
  • For aircraft equipped with Honeywell HG2021GD03 GNSSU, the GD03 may be upgraded to HG2021GD06. The antenna will also need to be replaced with an Active Antenna.
  • For aircraft equipped with HG2021GD02 GNSSUs, new SBAS GNSSUs (HG2021GD06 or KGS-200) and Active Antennas will be required to be purchased as there is no direct upgrade path.

In addition to supporting the GPS SA requirement for ADS-B Out, the HG2021GD06 GNSSU and KGS-200 are capable of supporting SBAS procedures.


The HG2021GD06 GNSSU is a 24-channel Satellite Based Augmentation System (SBAS) enabled receiver. SBAS provides GPS position corrections that result in highly accurate lateral and vertical position information necessary for LPV approaches. There are various SBAS systems around the world and the GNSSU is compatible with all currently defined systems.

Primus II Upgrade Supplemental Type Certificates

Several business jet maintenance, repair and overhaul centers have received Supplemental Type Certificates (STC) to upgrade your communication units and controllers.

The centers with certificates for Primus II upgrades include:

  • Duncan Aviation: Hawker 800 / 800XP, Citation 560 / 560XL
  • Flightstar: Learjet 40 / 45
  • Pro Star Aviation: Challenger 601, Citation 550 (II), 560 (V, Encore, Ultra), 560 XL (Excel), 650 (III, VI, VII), 750 (X), Learjet 40 / 45, Global Express (5000, 6000), Hawker 800 & 1000 series
  • TECHNICAir: Hawker 800 / 800XP
  • Capital Aviation: Hawker 800 /800XP
  • Emery Air: Hawker 800 / 800 XP