SELCAL and CPDLC

Long-haul and oceanic flights on VATSIM use two systems that you will not encounter on shorter domestic routes: SELCAL (Selective Calling) and CPDLC (Controller Pilot Data Link Communications). Both are designed to reduce the need for continuous voice monitoring over vast stretches of ocean where traditional radar coverage does not exist.

SELCAL
CPDLC (Hoppie)

What is SELCAL

SELCAL stands for Selective Calling. In the real world, it is a system used on oceanic and remote flights where pilots communicate with ATC over HF (high frequency) radio. HF radio is noisy and fatiguing to listen to for hours at a time, so SELCAL allows the crew to turn down the volume and wait for a tone.Here is how it works:

Each aircraft is assigned a unique 4-letter SELCAL code (for example, AB-CD)
When ATC needs to contact you, they send a signal matching your code
Your aircraft receives the tone and alerts the crew with a chime or indicator light
You then respond to ATC on the HF frequency

This means pilots do not need to constantly monitor a noisy HF frequency. They simply wait for their SELCAL tone to go off.

SELCAL on VATSIM

On VATSIM, SELCAL is simulated through your pilot client. The concept is the same - you provide a SELCAL code in your flight plan, and oceanic controllers can “ring” your aircraft when they need to reach you.

Getting a SELCAL Code

You have two options:

Register for a real SELCAL code at selcal.org - this gives you a unique code registered in the global database
Use a simulated code - many aircraft add-ons come with a default SELCAL code, or you can make one up using valid SELCAL characters (A through S, excluding I, N, and O)

A valid SELCAL code consists of four letters arranged in two pairs, where each letter within a pair is in alphabetical order. For example: AB-CD, DM-FS, or EK-GQ.

Adding SELCAL to Your Flight Plan

Include your SELCAL code in the Remarks section of your flight plan using the format:

SEL/ABCD

For example, if your SELCAL code is DM-FS, your remarks would include SEL/DMFS.

SimBrief has a field for SELCAL codes in your aircraft profile. Set it once and it will automatically appear in every flight plan you generate.

SELCAL Check

When you enter oceanic airspace, ATC may perform a SELCAL check to verify that your code is working.Once confirmed, you can reduce your volume and rely on the SELCAL alert to notify you when ATC calls.

When to Use SELCAL

Oceanic crossings (North Atlantic, Pacific, South Atlantic)
Long overwater segments where HF radio would normally be used
Any flight where oceanic ATC is active (Gander, Shanwick, New York Oceanic, etc.)

SELCAL is mainly relevant for oceanic flights. For domestic or continental flights, standard VHF communication is used and SELCAL is not needed.

What is CPDLC

CPDLC stands for Controller Pilot Data Link Communications. It is a text-based messaging system that allows pilots and controllers to exchange instructions, clearances, and requests digitally rather than by voice.Think of it as a structured text messaging system between your cockpit and ATC. Instead of speaking on a congested HF frequency, you send and receive typed messages.

CPDLC on VATSIM

On VATSIM, CPDLC is provided through the Hoppie ACARS system. Hoppie is a third-party service that simulates ACARS (Aircraft Communications Addressing and Reporting System) and CPDLC for the flight simulation community.

Setting Up Hoppie

Go to hoppie.nl and create an account. You will receive a logon code - this is your authentication key for the Hoppie network. Save it somewhere safe.

Configure your CPDLC client

Many modern aircraft add-ons have built-in Hoppie/CPDLC support:

PMDG 737/777/747: Built-in ACARS/CPDLC in the FMC CDU
Fenix A320: Built-in DCDU (Datalink Control and Display Unit)
FlyByWire A320neo: Built-in DCDU support
iniBuilds A310/A380: Built-in ACARS

If your aircraft does not have built-in support, you can use a standalone client like Hoppie ACARS Client or TopCat.

Enter your Hoppie logon code

In your CPDLC client or aircraft’s ACARS page, enter your Hoppie logon code in the appropriate field. This authenticates you on the Hoppie network.

Set your callsign

Your CPDLC callsign must match your VATSIM callsign exactly. If you are flying as ACA456 on VATSIM, your Hoppie callsign must be ACA456.

Connect to the Hoppie network

Activate or “log on” to the Hoppie ACARS system in your client. You should see a confirmation that you are connected.

Log on to the ATC station

Send a LOGON request to the controlling oceanic station. For example, if you are crossing the North Atlantic westbound, you would log on to CZQX (Gander Oceanic) or EGGX (Shanwick Oceanic).The controller will either accept or reject your logon. Once accepted, you have an active datalink connection.

Common CPDLC Messages

Message Type	Direction	Meaning
LOGON	Pilot to ATC	Request to establish a datalink connection with the ATC station
WILCO	Pilot to ATC	”Will comply” - acknowledging and accepting an ATC instruction
ROGER	Pilot to ATC	”Message received” - acknowledging receipt without compliance commitment
UNABLE	Pilot to ATC	”Cannot comply” - rejecting an instruction (include reason if possible)
REQUEST	Pilot to ATC	Pilot request (altitude change, route change, direct to waypoint, etc.)
CLEARED	ATC to Pilot	ATC clearance (oceanic clearance, altitude change, route amendment)
POSITION REPORT	Pilot to ATC	Reporting current position, altitude, and next waypoint with ETA
CURRENT DATA AUTHORITY	System	Indicates which ATC station has active control of your datalink

Example CPDLC Exchange

Here is what a typical oceanic clearance looks like via CPDLC:Pilot sends:

REQUEST OCEANIC CLEARANCE
ROUTE: NAT TRACK BRAVO
FL370 MACH .82
ENTRY POINT: DOTTY AT 0845Z

ATC responds:

CLEARED TO LONDON HEATHROW
VIA NAT TRACK BRAVO
MAINTAIN FL370
MACH .82

Pilot responds:

WILCO

Important Notes

Not all ATC positions on VATSIM support CPDLC. It is primarily used by:

Oceanic controllers (Gander, Shanwick, New York Oceanic, Santa Maria)
Some en route/Center controllers who have enabled Hoppie support

Always check whether the controller supports CPDLC before relying on it. If in doubt, use voice.

Even with CPDLC active, always monitor the voice frequency as a backup. ATC may use voice for time-critical instructions, traffic alerts, or if the datalink connection fails. CPDLC supplements voice communication - it does not replace it entirely.

Troubleshooting

CPDLC logon rejected or no response

Verify your Hoppie logon code is correct and active
Ensure your callsign matches your VATSIM callsign exactly
Check that the ATC station you are logging on to is actually online and supports CPDLC
Try logging off and on again after 30 seconds

Messages not sending or receiving

Check your internet connection
Verify the Hoppie server status at hoppie.nl
Ensure your CPDLC client is properly configured and connected
Some aircraft add-ons require the CPDLC system to be powered on via the overhead panel

Using CPDLC with no built-in aircraft support

If your aircraft does not have native CPDLC, use a standalone Hoppie ACARS client running alongside your simulator. It provides a separate window for sending and receiving CPDLC messages.

Introduction

Getting Connected

Pilot Clients

Communication & ATC

Advanced Operations

Resources

What is SELCAL

SELCAL on VATSIM

Getting a SELCAL Code

Adding SELCAL to Your Flight Plan

SELCAL Check

When to Use SELCAL

What is CPDLC

CPDLC on VATSIM

Setting Up Hoppie

Common CPDLC Messages

Example CPDLC Exchange

Important Notes

Troubleshooting

Next Steps

Oceanic Procedures

Radio Phraseology

​What is SELCAL

​SELCAL on VATSIM

​Getting a SELCAL Code

​Adding SELCAL to Your Flight Plan

​SELCAL Check

​When to Use SELCAL

​What is CPDLC

​CPDLC on VATSIM

​Setting Up Hoppie

​Common CPDLC Messages

​Example CPDLC Exchange

​Important Notes

​Troubleshooting

​Next Steps

Oceanic Procedures

Radio Phraseology

What is SELCAL

SELCAL on VATSIM

Getting a SELCAL Code

Adding SELCAL to Your Flight Plan

SELCAL Check

When to Use SELCAL

What is CPDLC

CPDLC on VATSIM

Setting Up Hoppie

Common CPDLC Messages

Example CPDLC Exchange

Important Notes

Troubleshooting

Next Steps