Voice Communication and Data-Link Transmission: ACARS, CPDLC, and D-ATIS

022-10-01Pablo Asensio Martínez2026-03-272 min

ACARS (Aircraft Communication Addressing and Reporting System)

ACARS is a digital datalink system for transmitting short messages between aircraft and ground stations. Developed by ARINC in the late 1970s, it remains the industry standard.

  • Purpose:
    • AOC (Airline Operational Control): Company messages (schedules, passenger data, maintenance tech logs).
    • ATC (Air Traffic Control): Clearances, requests, weather.
  • Onboard Management: The CMU (Communication Management Unit) manages the routing of messages. It connects to the MCDU (interface), VHF, HF, and SATCOM radios.
  • Terminology:
    • Uplink: Message from Ground $\rightarrow$ Aircraft.
    • Downlink: Message from Aircraft $\rightarrow$ Ground.

Transmission Media

ACARS and other datalink systems use various radio frequencies depending on availability and location.

  1. VHF (Very High Frequency):
    • Properties: Line-of-sight operation. Terrestrial range limited by curvature of Earth.
    • Speed/Quality: Good quality, moderate speed. Standard for continental/domestic operations.
  2. SATCOM (Satellite Communication):
    • Properties: Uses UHF band. Global coverage (except sometimes Polar). No line-of-sight limitation with ground stations.
    • Speed/Quality: Highest data rate, immune to ionospheric interference. High signal quality.
  3. HF (High Frequency):
    • Properties: Long range (Oceanic/Remote) due to ionospheric reflection ("skywave").
    • Speed/Quality: Lowest data rate, poor quality due to static and interference. Used only when VHF/SATCOM are unavailable (e.g., polar regions without Iridium satcom).

Applications

CPDLC (Controller-Pilot Data Link Communications)

A text-based method for pilots and controllers to exchange messages (Clearances, Requests, Reports).

  • Benefits: Reduces frequency congestion, eliminates "hearback/readback" errors, allows complex instructions to be reviewed.
  • Examples: Oceanic Clearances, Route modifications, Frequency changes.

D-ATIS (Digital ATIS)

  • Receives the ATIS (Automatic Terminal Information Service) text message via datalink.
  • Displayed on the MCDU or printed. Eliminates the need to listen and transcribe the audio broadcast.

DCL (Departure Clearance)

  • Obtaining the pre-departure clearance via datalink before engine start.
  • Improves efficiency and reduces ramp congestion/workload.