Testers & Simulators

ACARS CMU Simulator

ACARS CMU Simulator

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

The CMU Simulator 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.

The Aircraft Communications Addressing and Reporting System (ACARS) 

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.

Configurable Parameters
  • 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
  • Tail #
  • Flight #
  • ACARS Label
MSNAutomatic or manual MSN selection
MSN pool for automatic selection
MSN for manual selection 
TerminatorETX or ETB
BCS validityCorrect or incorrect
Message textAutomatically generated, manually specified, or read from file
Max and min length for automatic generation
Downlink blocksNumber to send, or total duration
AckAutomatic or manual Ack of uplinks
Use last received or manually specified UBI for Ack of uplink
Timeout for Ack of downlink
Link setupAutomatic or manual link setup
Automatic or manual media advisory
Logging enableACARS blocks sent
ACARS blocks received
ARINC labels sent
ARINC labels received
StatisticsBlocks sent/received
Acks sent/received/missed
Max/min/avg Ack latency
StatusCMU state
SDU state
Sat ID
Service type
Last DBI sent
Last UBI received
Last MEN sent
CMU Simulator Configuration for over-the-satellite operation
CMU Simulator Configuration for local operation using Classic Aero
Host platform BPLT, GDU, or PC with BSCR software
ARINC-429 interface Abaco CEI 520A, RCEI-530, or RAR-USB
Square Peg Communications Inc.
4017 Carling Avenue, Suite 200 
Ottawa, ON, Canada K2K 2A3
Tel + 1 613 271 0044
Fax+ 1 613 271 3007
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