ATPL Theory

Cpdlc Overview

CPDLC – Simple Explanation

CPDLC (Controller Pilot Data Link Communication) is a text-based messaging system between pilots and ATC that reduces voice radio use.

How it works

  1. Pilot logs on to the ATC unit
  2. Messages are sent via data link (VHF / SATCOM / HF)
  3. Messages appear on the CDU / DCDU
  4. Crew reads, accepts, rejects, or replies
  5. Some clearances can be loaded into the FMS

Message Types

Requests (Pilot → ATC)

  • Altitude request
  • Speed request
  • Route request
  • Clearance request
  • Emergency request
  • Position report
  • Free text

Responses (Pilot → ATC)

  • Replies to ATC questions
  • Uses pre-formatted options (e.g. ABLE / UNABLE / STANDBY)

Reports (Pilot → ATC)

  • Mainly position reports
  • Can be automatic or manual

Key Characteristics

  • Messages are pre-formatted (global standard)
  • Reduces radio congestion
  • Reduces misunderstandings
  • Used mainly in oceanic, remote, and high-density airspace

CPDLC = standardized text messages between pilots and ATC for clearances, requests, and reports.

Position Reports and Handling Uplinked Clearances:

Position Reports (CPDLC / ADS-C)

  • A position report sends the aircraft’s:

    • current position
    • level
    • speed
    • time
    • next waypoint

  • Can be automatic or manual

  • Most common CPDLC report

  • Often triggered by:

    • ATC request
    • ADS-C contract
    • a clearance (e.g. “REPORT LEAVING FL340”)

Example:

  • ATC: CLIMB FL380. REPORT LEAVING FL340. REPORT REACHING FL380

  • Aircraft automatically sends:

    • report leaving FL340
    • report reaching FL380

Handling Uplinked Clearances (Airmanship)

Uplinked clearances must be treated exactly like voice clearances.

Standard crew process:

  1. Both pilots read and understand the message independently

  2. Both pilots confirm it is achievable

  3. Clearance is correctly set in:

    • FMS and/or
    • MCP / FCU

  4. Crew checks the aircraft is responding correctly

    • verify modes on the FMA

  5. Acceptance and compliance are sent back to ATC

    • both pilots check the downlink before sending

Crew Handover (long-haul)

  • Outgoing crew briefs:

    • CPDLC / ADS-C status
    • expected messages or contracts

Key Exam Lines

  • Position reports = automatic or manual aircraft status messages
  • Uplinked clearances require full cross-check, setup, mode confirmation, and ATC acknowledgement
  • Data link clearances are never “actioned blindly”