A discussion on voice CTAF

All those AFV updates you've been waiting for!

Posted by The BoG - May 5, 2019


It has been a while since we have given you an update on VATSIM’s technical development. This is primarily because we have been very busy preparing for the rollout of Audio for VATSIM (AFV), our new voice technology. We will provide an update on AFV as well as other technologies currently in development to enhance your VATSIM experience.

Technical development on VATSIM

Technical development on the network has seen a steep change in the past 12 months. We’ve had everything from limited interventions by small groups of people all the way to much larger improvement projects involving large teams from our community of developers. Most of these projects have been back-end and thus are largely invisible to you, the members, outside of a more stable online flight simulation experience. Over the past year, we have been through a journey, striving to make our development cycle more transparent, and we have learned a lot of things the hard way. Thankfully, one development cycle is nearing completion and that one is the most major advancement in VATSIM’s history, “Audio for VATSIM”.

We want to find ways to streamline our development cycles and find ways to not only be more visible and transparent to the community but also owned by the community as well. One of our ideas for the future is to make it easy for VATSIM members to submit technical items to a wish-list through a single point of contact. We also want to make it easier for volunteers to develop for VATSIM without all the red tape we have had in the past.

Audio for VATSIM

Over 3,000 of you signed up to be part of the first public test and we are excited to show off the new product to as many of you as possible! The primary focus of the beta test is to stress the infrastructure and receive feedback from our users. We hope to announce dates within days.

Over last weekend, significant work was done by our development team to complete native integration of AFV with the vPilot pilot client. This first public beta test will run as an event on a dedicated VATSIM FSD server instead of a general one you currently use to connect. This is because the old and new voice architectures are not able to be run side by side on the same server without causing problems for VATSIM pilots who are not part of the beta.

We have been working hard server-side as well to make sure everything is in place for the network-wide launch. Since the two voice architectures can not run together, when we launch network-wide, it will have to be done all at once. We will turn off the current voice codec and switch over to AFV.

We will give you plenty of time prior to the launch as you will have to update your pilot clients or download the external client to use AFV, as this will be required to continue to use voice on VATSIM.

We know the whole community is eager for news and, of course, a release as soon as possible. This is what we’re working towards, and this project is our #1 priority.

Now for some technical details.

VHF simulation incoming

The new voice system incorporates a range of cool features; VHF range simulation, VHF radio simulation, over-transmission simulation, etc.

Here is how the VHF range, and therefore our 'simulation' works:

There are numerous calculations for VHF range, but the primary variable is altitude. The higher the altitude, the further the range. A common formula to find VHF range is, find the square root of the altitude and multiply that number by 1.5. If you can follow that formula, you can then work out that the VHF range at 30,000FT is approximately 260NM and that VHF range at 10,000FT is 150NM. Two aircraft MUST be within range of one another to send and receive (TX/RX) transmissions between them. Take a look at this picture:

However, if the orange aircraft moved to the east, the aircraft would not be able to hear one another as their transceivers are not within range. See here:

If the orange aircraft climbs, they may find themselves back within range to allow the black aircraft to RX them. Does that make sense? Have I confused you? I hope not, but I will admit that when Gary and I talked through the initial concept I confused myself on this very topic. So when you do start using voice CTAF on VATSIM, please remember these quirks with VHF range/coverage and maybe that's the reason why you can hear your friend, but they can't hear you!

Voice CTAF!

A number of you will be wondering what CTAF means. Common Traffic Advisory Frequency (CTAF) is a frequency used by pilots for air-to-air communications at non-towered aerodromes. CTAF may also be known as a MULTICOM or UNICOM but these terms actually have slightly different meanings. UNICOM is actually an air-to-ground station at uncontrolled aerodromes and MULTICOM means a 'multitude of CTAFs grouped together' - very similar to the purpose that 122.8 has served for many years. Pilots use the CTAF to ensure a safe flow of departures and arrivals by giving position reports and acknowledging other aircraft in the vicinity of the aerodrome. VATSIM is globally adopting the word ‘CTAF’, to accurately describe our air-to-air communication systems!

VATSIM will start by supporting global, restricted range, voice CTAF (frequency 122.800 or as otherwise defined). However, after the initial rollout, we'll be hard at work readying the next phase for rollout, which includes developing training, policies, and procedures that support global discrete (real-world) frequency, voice CTAF!

The global voice CTAF frequency will be 122.8 (as it always has been) and this frequency will be limited to a maximum range of 15NM (enough for negotiating arrival and departure sequences in and around airports). We believe that 15NM will be a suitable limit, however, this may need to be adjusted.

CTAF will be limited to a maximum range of 15NM (enough for negotiating arrival and departure sequences in and around airports). We believe that 15NM will be a suitable limit, however, this may need to be adjusted.

Before you say it, I know what you are thinking. Yes – AFV absolutely introduces the capability of individual CTAF frequencies worldwide. However, we believe a staggered approach to this is necessary. Here’s why:

- VATSIM is a network for aviation enthusiasts (both pilots and ATC).
- We do not require you to undertake a ‘Private Pilot Licence” before flying on the network.
- We do not require you to purchase charts and maps.

We want VATSIM to be as accessible to as many people as possible and the reality is that not everyone has the knowledge and resources to operate a (simulated) aircraft in the same way – remember that VATSIM members have varying levels of experience, from enthusiasts all the way to real-world pilots (like me).

That said, we know that ‘discrete’ or ‘real-world’ individual CTAF is the path that we want VATSIM to head down. So, we’ll give ourselves some time to see how we, as a community, deal with voice CTAF on 122.8 and that time also gives us the opportunity to develop a training system for those less-experienced members. We are also developing a VATSIM Aeronautical Information Service, which will provide users with (ideally) charts, frequencies, airspace information, navigation information and provide a global source for division sector files and mapping services.

Here’s a tip – keep the CTAF (122.8) in COMM 2 at all times!

Global ATIS/AWIS Bots

Another cool feature that AFV has is ATIS (Aerodrome Terminal Information Service) or AWIS (Automated Weather Information Service) bots. The bots will be broadcasting at airports, when there is no controller online, using preferential runways/rules (as set by the division) and real-world weather. A very cool feature to facilitate and coordinate movements at uncontrolled aerodromes. The ATIS bots even have accents, from British to American, Indian and Australia (the possibilities are endless!) The photo below shows the bots ... wait for it ... in the UK only!

Well – this blog has gotten reasonably lengthy and we need to get back to work on more important things. I hope this was informative and I look forward to providing more updates very soon.

Thank you for reading and thank you for your continued support!