Communication System

ARINC, ACARS & CPDLC — ATPL Quick Guide

ARINC Aeronautical Radio Incorporated is a company and standards body. It defines aviation data formats and protocols (e.g. ARINC 424 for nav databases) and originally designed ACARS. ➡️ ARINC sets the rules; it is not a communication service.

ACARS Aircraft Communications Addressing and Reporting System. A datalink network/protocol that sends text messages between aircraft and ground.

• Uses VHF, HF, or SATCOM
• Used for AOC (company, maintenance) and some ATC messages
• Basis of early FANS (FANS 1/A) ➡️ ACARS is the “pipe” that carries data.

CPDLC Controller–Pilot Data Link Communications. An ATC text-messaging application for clearances, requests, and reports.

• Messages are pre-formatted and standardised (ICAO)
• Often runs over ACARS (sometimes over ATN B1 or SATCOM)
• Voice remains primary, CPDLC is secondary ➡️ CPDLC is the ATC messaging application.

• ARINC = standards & ACARS designer
• ACARS = datalink network
• CPDLC = ATC text communication application

Below is a clean, structured explanation of ARINC, ACARS, and CPDLC, keeping the distinctions precise and operationally accurate.

ARINC

What it is

Aeronautical Radio Incorporated (ARINC) is a private aviation company that:

• Designed ACARS
• Acts as a de-facto global standards body for avionics data formats and communications

Key point: ARINC defines how aviation data is structured and exchanged — it is not itself a communications network.

Role

ARINC publishes widely used avionics and data standards, including:

• ARINC 419-3 – Digital Data System Compendium
• ARINC 424-21 – Navigation System Database
• ARINC 428 – Avionics Network Design Considerations

These standards define:

• How navigation data (SIDs, STARs, approaches) are coded
• How avionics systems store, interpret, and exchange data

Summary: ARINC = standards provider and original ACARS designer, not a communications service

ACARS

What it is

ACARS (Aircraft Communications Addressing and Reporting System) is:

• A first-generation aircraft datalink system
• Developed by ARINC
• A network + protocol, not an application
• Based on telex-style text messaging

Media / communication methods

ACARS can use multiple physical links:

• VHF (line-of-sight, ~2.4 kb/s)
• HF (HFDL) – long-range, lower reliability
• SATCOM (e.g. Inmarsat)

Modern systems automatically switch between VHF, HF, and SATCOM based on availability.

What it is used for

ACARS carries messages between aircraft and:

• AOC (Airline Operations Control)

  • Dispatch
  • Engineering
  • Maintenance

• ATC (in some regions and early datalink implementations)

Typical message content:

• Weather data
• Flight plans
• Administrative / commercial messages
• Engine and maintenance reports
• Event-triggered system reports

Message formats:

• Pre-formatted reports (position, faults, requests)
• Free-text messages

Place in FANS

ACARS underpins first-generation FANS (FANS 1/A) and was later adapted to:

• Carry CPDLC messages
• Support ADS-C position reporting

Summary: ACARS = the transport layer that moves aviation text data over VHF / HF / SATCOM

CPDLC

What it is

CPDLC (Controller–Pilot Data Link Communications) is:

• A software application
• Enables text-based ATC–pilot communication
• Part of the global CNS/ATM modernization concept

CPDLC defines what the messages mean, not how they are physically transmitted.

How it communicates

CPDLC can run over multiple datalink paths:

• ACARS (most common worldwide)
• ATN B1 (notably Europe)
• SATCOM

All CPDLC-equipped aircraft have VHF datalink; HF and SATCOM are optional.

Message definitions are standardized by International Civil Aviation Organization (ICAO) in the GOLD (Global Operational Data Link Document).

What it is used for

CPDLC handles structured ATC communications, including:

• Requests (e.g. climb, route change)
• Clearances
• Reports (especially in oceanic / non-radar airspace)

Pilot workflow example:

1. Pilot enters request (e.g. CLIMB DUE WEATHER)
2. System shows a VERIFY page
3. Message is sent
4. ATC replies with an uplink clearance
5. Pilot selects ACCEPT / REJECT / STANDBY

Relationship to voice and ADS

• Voice remains primary, even in Datalink Mandatory airspace

• CPDLC is secondary / backup

• ATC units may use:

  • ADS only
  • CPDLC only
  • Both together

Summary: CPDLC = the ATC messaging application that often rides on top of ACARS

Putting it all together

Conceptual stack

ARINC
 └─ Defines standards (data formats, protocols)
     └─ ACARS
         └─ Datalink transport (VHF / HF / SATCOM)
             └─ CPDLC
                 └─ ATC–pilot text messaging application

One-line definitions

• ARINC Standards body and original ACARS designer

• ACARS Aviation datalink network/protocol for operational and ATC messages

• CPDLC Structured ATC–pilot text communication application

ARINC vs ACARS vs CPDLC, with roles clearly separated.

✈️ ARINC vs ACARS vs CPDLC

Core Idea (memorise this)

• ARINC = standards & network provider
• ACARS = data transport system
• CPDLC = ATC communication application

1. ARINC

What ARINC is

• A standards body and service provider

• Defines:

  • avionics standards (e.g. ARINC 429, 702)
  • message formats
  • ground networks

What ARINC does

• Operates ACARS ground networks (one provider)
• Provides communication infrastructure for airlines and ATC

👉 ARINC = rules + pipes on the ground

2. ACARS (Aircraft Communications Addressing and Reporting System)

What ACARS is

• An air–ground data link system
• The transport layer

What ACARS does

• Carries many message types:

  • CPDLC
  • ATIS / weather
  • AOC (airline messages)
  • Maintenance data

How

• Uses VHF / HF / SATCOM
• Managed onboard by CMU / ATSU

👉 ACARS = how data is sent

3. CPDLC (Controller Pilot Data Link Communication)

What CPDLC is

• An ATC communication application
• ICAO-standardised message set

What CPDLC does

• Sends:

  • clearances
  • instructions
  • requests
  • reports

• Reduces voice radio use

How

• Runs on top of ACARS (or ATN)
• Requires ATC logon

👉 CPDLC = what ATC and pilots say

Side-by-Side Comparison (Exam Gold)

Simple Analogy (Very Effective in Exams)

• ARINC = Internet standards + ISP
• ACARS = Internet connection
• CPDLC = Email messages

ARINC provides the standards and ground network, ACARS is the data link system that transports messages, and CPDLC is the standardized ATC communication application carried by ACARS.