Acars Shortly

Short, clear, explanation of ACARS during a flight:

ACARS – Simple Flight Flow

1. CMU / ATSU

• The brain/router of ACARS
• Chooses VHF / HF / SATCOM
• Sends and receives all messages

1. On the ground (preflight)

• Crew receives clearance, weather, NOTAMs
• Messages appear on CDU / DCDU
• Alert light/caption turns on
• Messages can be printed

1. Taxi & takeoff

• ACARS automatically sends OUT and OFF times
• Maintenance data may be sent to the ground

1. Climb & cruise

• FMS provides position data
• ACARS sends position reports
• ATC and airline send messages (CPDLC / AOC)
• Crew reads and replies via CDU / DCDU
• Some messages can be loaded into the FMS

1. Maintenance

• Faults are downlinked automatically
• Ground can request diagnostics
• Results are sent back via ACARS

1. Descent & landing

• Crew receives arrival weather / instructions
• ACARS sends ON and IN times

Component Roles (one-line each)

• CMU/ATSU: routes messages and selects network
• FMS: flight data source (route, position)
• CDU/MCDU: pilot interface for ACARS
• DCDU: dedicated ACARS display (older aircraft)
• Printer: prints uplink messages
• Maintenance computer: sends faults/diagnostics
• ATC annunciator: alerts crew to ATC messages