ACARS CMU Emulator



The SPCI CMU Emulator replaces the ACARS Communications Management Unit for end-to-end testing of the ACARS system.  It communicates with an Inmarsat Classic Aero or SB-Safety Satellite Data Unit (SDU) via ARINC-429 to generate and receive ACARS traffic.

The CMU Emulator is implemented as a Physical Layer Tester script, and can run on either a BPLT or a GDU.  In addition, it can run on a standard PC using a special version of the GDU or BPLT software.  In all cases, a suitable ARINC-429 interface must be present.

For local testing, a GDU hosting the CMU Emulator can also run the GES Emulator facility to act as the ground side of the ACARS network (see Local Operation under CMU Emulator Configuration). In this case the ACARS messages sent by the CMU Emulator are displayed in the Link Service User window of the GES Emulator. Uplink messages can also be sent to the CMU Emulator from this window.

The CMU Emulator provides flexible control over the content and timing of the ACARS messages sent.  Messages can be entered interactively or read from files, and can be sent individually or periodically at a specified rate.  Traffic statistics are calculated, and the messages sent and received are logged.

  • CMU Emulator Configuration for over-the-satellite operation


    CMU Emulator Configuration for local operation using Classic Aero



  • Functions


    Set up link to SDU and send media advisory
    Send downlink blocks
    Send Ack or Nak
    Send UTC request, display UTC report
    Display SDU and ACARS status
    Display messaging statistics
    Log ACARS blocks sent and received
    Log ARINC labels sent and received

    Configurable Parameters


    Tail #
    Flight #
    ACARS Label


    Automatic or manual MSN selection
    MSN pool for automatic selection
    MSN for manual selection


    ETX or ETB

    BCS validity

    Correct or incorrect

    Message text

    Automatically generated, manually specified, or read from file
    Max and min length for automatic generation

    Downlink blocks

    Number to send, or total duration


    Automatic or manual Ack of uplinks
    Use last received or manually specified UBI for Ack of uplink
    Timeout for Ack of downlink

    Link setup

    Automatic or manual link setup
    Automatic or manual media advisory

    Logging enable

    ACARS blocks sent
    ACARS blocks received
    ARINC labels sent
    ARINC labels received


    Blocks sent/received
    Acks sent/received/missed
    Max/min/avg Ack latency


    CMU state
    SDU state
    GES ID
    Sat ID
    Service type
    Last DBI sent
    Last UBI received
    Last MEN sent

  • Host platform

    BPLT, GDU, or PC with BSCR software

    ARINC-429 interface

    Abaco CEI 520A, RCEI-530, or RAR-USB

  • The Aircraft Communications Addressing and Reporting System (ACARS) allows text messages to be communicated between aircraft and ground systems for air traffic control, aeronautical operational control, and airline administrative control

    The airborne equipment consists of an ACARS Management Unit (MU) or a Communications Management Unit (CMU) operating as an ACARS MU.  The MU or CMU can be connected to ancillary equipment such as the Flight Management System (FMS), Digital Flight Data Acquisition Unit (DFDAU), or cockpit printer.

    ACARS messages are transmitted over one of three air-ground subnetworks: HF, VHF, or Satcom.  The router function built into the MU/CMU determines which subnetwork to use when routing a message from the aircraft to the ground. The airline operator provides a routing table that the CMU uses to select the best subnetwork.

    The Satcom interface provides a satellite-based data link capability.  To access the Satcom subnetwork, the ACARS CMU is connected to the Satellite Data Unit (SDU) by a pair of ARINC-429 data buses.

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