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Effective Use of Guard Frequency

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Jarrett I. (1016071)


You're flying along from Miami to Chicago talking to various air traffic control centers while en route. About halfway to Chicago, you notice radio silence; you try calling air traffic control with no answer. You check your microphone settings, everything seems to be working normal. What do you do? 

Another day, you're flying a Cessna 172 VFR in your local practice area without talking to air traffic control when all of the sudden you notice black smoke coming out of the engine. You see an airport in the distance and you head towards it but you have no idea what airport this is. You need assistance from air traffic control, but have no time to figure out the proper frequency to contact, obviously, you are handling an emergency. What do you do?

In both of these scenarios, GUARD frequency (VHF 121.5 and UHF 243.0) can be an effective tool. This is a frequency reserved for emergency transmissions as well as for aircraft that have missed a check in with ATC or not sure what frequency they should be on. 121.5 is used all over the world and nearby air traffic controllers are always monitoring this frequency.

In the first example we described, you could switch to 121.5 and transmit: "Delta 123, on GUARD, I lost contact with Memphis Center, can someone advise which frequency I should be on?" On the reverse side of things, air traffic controllers can use GUARD to locate an aircraft they were expecting to hear from or that have not been responding. For example, an air traffic controller could say: "American 123, Memphis Center, on GUARD, if you hear this message, switch to my frequency on 132.4." Sometimes an aircraft may be unresponsive because they are out of range of an air traffic controller's radio transmitter. Since there are often aircraft positioned in different parts of a center controller's airspace, a controller may ask another pilot for assistance to relay a message on GUARD in the hopes that their location will transmit a better signal to the unresponsive aircraft. In this scenario, GUARD provides an excellent resource in ensuring all aircraft are accounted for.

In the second example, we see the potential use of GUARD in an emergency scenario. The pilot could switch to GUARD and state that they have an emergency and are landing at the nearest airport. Since all air traffic controllers monitor GUARD, a radar controller can transmit on GUARD and provide better assistance to the pilot by issuing radar vectors, recording important information pertaining to the emergency, and coordinate for crash fire and rescue to be ready at the diversion airport. 

Interesting to know as well, when an ELT beacon goes off, it transmits an aural signal on the GUARD frequency. Organizations like the Civil Air Patrol actually practice triangulating and locating a beacon to find the location to prepare for search and rescue missions in the event an aircraft crashes. The beacon signal from ELTs almost sounds like a siren.

IMG_20190822_233444109.thumb.jpg.293aef94bbac8c698c0c9e620c31ca82.jpgOne final example worth mentioning is the DOD (e.g. Air Force, Coast Guard) monitor GUARD as well. Aircraft crossing over our international borders without following proper ADIZ entry procedures can be intercepted by military aircraft who will use GUARD frequency in an attempt to establish communication with the violator. If two-way communication is established on GUARD, the intercepting aircraft can provide further instructions to the pilot as necessary.

In conclusion it is strongly recommended, and in most instances required, for pilots to always monitor GUARD 121.5 on their second radio. In fact, airlines require crews to monitor 121.5 on a second radio when the radio is not needed for other operational reasons. Monitoring GUARD provides an extra layer of safety and if you accidentally transmit on GUARD, don't worry, there are plenty of pilots that will key up in a funny voice to remind you "You're on GUARD"... hopefully that doesn't happen during a time when you really need it.

On POSCON, we simulate the GUARD frequency on both VHF and UHF frequencies to provide an ultimate realistic experience. Next time you find yourself on the network in one of these scenarios, try the GUARD frequency. For more information, check out the AIM 6-3-1.

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    1. Network Technology

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      Recent Entries

      Andrew Heath
      Latest Entry

      By Andrew Heath,

      On April 1st, 2020 we officially began approving invites to the POSCON Invite-Only Beta. We are now almost two months into our release and it still brings me great excitement every time I see a new user experience POSCON features for the first time. We learned a great deal in the first few days and weeks after the initial release. One thing that became abundantly clear was that we need to have a central location to refer users to in regards to what features are functional, what features are still in development, and what features are planned for the future. In addition, there still seems to be some confusion surrounding the invite process, so I am going to attempt to clarify all these items in this development update.

      Before I began, I think it is worth mentioning that we created a Frequently Asked Questions (FAQ) area that may contain answers to some of the questions that may not be answered in this blog post.

      While there is no doubt that we have deviated from the FSExpo 2019 Roadmap to Release timeline, we are doing our best to keep on track. Right now, I think it is safe to say we are in Invite-Only Beta, Phase 2. Here is a quick recap on the original plan for Invite-Only Beta, Phase 2 and what may or may not have changed since the announcement was first released:

      • Pilots will require an invite code and subsequent approval in order to participate
        • Status Update: This is still the case. Currently, any approved member with access to the network also has the ability to invite two additional registered users to the service by clicking here. Once invited, those members will be placed into a holding pattern until they are approved by the POSCON staff. There is no set time frame on when these approvals are distributed - we approve people when the team feels comfortable to receive additional members. This two-step process was designed to meter the flow of incoming members and minimize the amount of support requests we receive. More information on the invite process is discussed below.
      • ATC will be hand-picked by POSCON staff and will be required to sign an NDA
        • Status Update: This is still the case. We have been testing ATC regularly now, but we rarely advertise when or where we will be conducting these testing sessions. This strategy is employed on purpose in order to not overwhelm the controllers as they test new features. On a few occasions, we have given some advance notice of when ATC will be online, but right now those instances are rare.
      • Operating times will be schedule limited
        • Status Update: This is no longer true. Before we released, we separated the network into a development environment and a production environment which enables us to minimize interruptions to the users as we add new features. With the exception of a few hot-fixes in the early days after releasing, we have made considerable effort to inform all beta testers of scheduled maintenance well in advance of a server restart. In order to facilitate this, we created a System Status Monitor page which can be used to view the status and scheduled down times of our applications: https://status.poscon.net/
      • ATC coverage will be limited to areas selected by POSCON
        • Status Update: This is still the case. ATC testing has been limited to the areas where the facility data is most developed; however, our Facility Data Team has been tirelessly working on other areas around the world as well. Here is just a brief overview of what they have done:
          • 170 FIRs have been worked on.
          • 7856 independent ATC sectors have been created.
          • 7053 independent VHF transceiver sites have been located and entered into our database.
          • 1801 independent radar sites have been located and associated with 73 different radar types.
          • In addition to the above, below are just a few images of the FIRs that have been worked on:













      • Number of users was planned at between 1000-2000
        • Status Update: This is still the case. As of May 23rd, 2020 we have invited and approved 1278 registered users.
      • NDA is not required for Invite-Only Beta, Phase 2
        • Status Update: This is still the case. You are not required to sign a non-disclosure agreement (NDA) unless you are hand-picked to be an ATC. We will continue to maintain a select group of NDA pilot beta testers to test new features in our development environment.


      Invite Process - How does it work?

      As mentioned earlier, the invite process consists of two steps: INVITED and APPROVED. Here is how it works:

      1. Lets assume you joined the POSCON Public Discord first and then realize you are interested in joining the network. If this is the case, you are considered an "Enthusiast" and will be assigned that tag automatically in our Discord server.
      2. Now you decide to register at https://www.poscon.net and complete the checklist items which include: ensuring your birthday is set correctly and your Discord ID is connected to your POSCON account. At this point, you are now considered a "Registered User".
      3. If you are lucky, you may be invited by an approved member as their guest and you will receive an email from POSCON. If this happens, you are still considered a "Registered User".
      4. Please wait patiently until you are approved by POSCON staff. When approved, you are now a "POSCON Member" and have access to our HQ website and are able to download the Launcher Client. This is the point at which you can now connect to POSCON.

      The time between steps 3 and 4 is an unknown. It could be a matter of days, weeks, or even months. It all depends on where we are at with our development and whether we are ready to accept new members.

      If you find yourself in limbo, the best thing you can do is join our Public Discord and participate in the discussions until you are invited and/or approved.


      What is working, what is in development, and what are the future plans?

      Voice System

      Working Features:

      • Ground-based transceiver locations have been added for most ATC facilities.
      • Auto gain control.
      • Propagation of transceiver locations to the Radar Client.
      • Our voice library supports the option for separate PTTs per radio (e.g. VHF #1 and VHF #2), separate volume controls per radio, and separate audio devices per radio.
        • NOTE: The pilot clients do not currently support this yet.
      • Full VHF simulation including:
        • 8.33 kHz and 25 kHz spacing.
        • Terrain line-of-sight processing.
        • Beat simulation.
        • End-of-transmission popping tones.
        • Wavelength simulation.

      In Development:

      • ATISAWOS, and ASOS automatic audio broadcasts on the proper frequencies.

      Future Plans:

      • HF and UHF.
      • There are many more features planned, but we are going to keep those a secret for now.

      Website, Training, & Administration

      Working Features:

      • Fully GDPR compliant.
      • Integrated support system.
      • Basic flight statistics.
      • ICAO 2012 formatted flight plan form includes:
        • An integrated help tutorial provided on the page.
        • The form validates while entering data.
        • Auto-fill from SimBrief output.
      • Feedback and generic points system works.
      • Live Map used to view online traffic (updates every 2 seconds).
        • Users can leave feedback about each other using the map.
        • Moderators can initiate ghosting, disconnects, and bans using the Live Map interface.
      • Pilot Client Web UI, which can be accessed on any device with an internet connection (see below for more details).

      In Development:

      • Converting HQ to a new language and framework.
      • Moving elements of the ICAO 2012 flight plan to the server.
      • Live Map version 2.0 will use custom tiles and our own tile server. The map will also contain a 2D option for performance reasons.
      • Various upgrades to user-interface and user-experience throughout the HQ.

      Future Plans:

      • Upgrades to the user profile, including notifications.
      • Pilot and ATC scheduling system.
      • Advanced statistics center.
      • Additional ways to earn and lose POSCON points.
      • Additional CBTs with progression quizzes.
      • Airport Advisory Page system. This system will allow Divisions and Sub-Divisions to create informational pages about their airports that will be viewable by all pilots.

      Pilot Clients & Web UI

      Pilot Clients

      Working Features:

      • Both pilot clients support a high refresh rate. Models will update 15 times a second for a smooth visual experience.
      • Enhanced ground-clamping using various methods for a smooth experience regardless of differences in terrain.
      • Model matching. Here is how we handle model matching with the various platforms:
        • For X-Plane, the models are distributed with the pilot client itself and contain custom model matching logic.
        • For FSX/P3D, we have integrated the FLAi model set through our Launcher Client application (see below for more details).
      • ICAO equipment and airline code validation.
      • Accurate ground speed monitoring (X-Plane Only).
      • VHF push-to-talk activation indications.
      • VHF volume sliders on the native user-interfaces.
      • AI model sounds and controls (X-Plane Only).
      • The ability to control the maximum number of AI planes that will be displayed.
      • In-game notification of ghosting and disconnects with explanations.
      • The ability to manually toggle ghost mode or request to unghost.
      • Automatic detection of change in aircraft.
      • X-Plane 11.50 Vulkan support.
      • Moderator messaging directly into the pilot clients.
      • Automatic ghosting for:
        • Sim rate increase, entering slew mode, using replay mode, or deliberate pausing (this can also sometimes be triggered by accessing a sim menu).
          • If you are on the ground and not moving, pausing is allowed.
        • Connecting on or re-positioning to a runway (through a menu) will prevent connection or disconnect the user as applicable.

      In Development:

      • We are fixing various issues with models and model matching (X-Plane).
      • A new multiplayer library is being integrated (X-Plane).
      • A new native user-interface is being added (X-Plane).

      Future Plans:

      • We plan to make full use of the voice system by adding separate PTTs per radio (e.g. VHF #1 and VHF #2), separate volume controls per radio, and separate audio devices per radio.
      • HF and UHF integration.
      • There are many more features planned, but we are going to keep those a secret for now.

      Here is an Easter egg for those who have gotten this far in the blog: If you can name all the FIRs (the colored ones) depicted above correctly, then you can get an instant invite and approval to use POSCON. DM your answers to me directly. Offer expires May 27th at 2359 UTC.

      Web UI

      Working Features:

      • Some functions of CPDLC (Controller-Pilot Data Link) are operational such as the login function and automatic squawk code assignment.
      • Real-world FAA D-ATIS (Digital Automated Terminal Information Service) broadcasts are integrated and can be requested in real-time by pilots.
        • The voice portion of D-ATIS is not working yet, only the text portion.
      • METAR and TAF reports can be requested in real-time by pilots.
      • Radio syncing.
      • Ghost and unghost toggle.
      • Disconnect.

      Future Plans:

      • Additional CPDLC functions, including heading, speed, and altitude changes.
      • Full pilot report functionality.
      • Approaching online ATC awareness messages.

      Launcher Client

      Working Features:

      • The ability to download, install, launch, and update all available network software.
      • Token authentication. Once you enter your username and password once, the Launcher Client will take care of the rest.
      • image.png.f38b09c14b39359d078f8229fff838cf.png We added some new functionality to these buttons. The button on the left refreshes the Launcher Client, the middle button minimizes the Launcher Client, and the button on the right will send the Launcher Client to the system tray.
      • Once in the system tray, right-clicking on the Launcher Client icon will bring up a menu that will allow users to: reload, clean temp files, and quit the application.

      In Development:

      • Adding libraries that will utilize a new content delivery method through a download server.
      • Converting the application to a different framework.
      • Working on moving away from our web dependent set up.
      • User-interface changes such as adding a download progress bar, information display, and a direct link to Discord from the title bar.
      • Working on integrating Live Map version 2.0 through the Launcher Client.

      Future Plans:

      • The plan is to embed the Pilot Client native user-interfaces directly into the Launcher Client. There will be no need to launch a the Pilot Clients anymore after this is completed.
      • Once the back-end work is completed for the above, a new user-interface will be needed to accommodate the integration.


      Next steps?

      The next step for the POSCON team is simple: we will continue to work hard on bringing you the next-generation flight sim network.

      While we do that, we encourage you to join our Public Discord and participate in the discussions there. Typically, the most up-to-date information about the project is released on our Discord first.

      That's it for now! If you have any questions that have not been answered in the FAQ or in this blog post, feel free to comment below.


    2. Jarrett I. (1016071)
      Latest Entry

      By Jarrett I. (1016071),

      I'm sure you've seen those four letters before - RVSM - and you may have a fundamental knowledge about the airspace, but do you know why it exists? Here are the answers to the most basic questions:

      1. Where do we find RVSM airspace? Higher cruising altitudes.
      2. What happens in RVSM airspace? Airplane separation is reduced vertically.
      3. Why does RVSM airspace exist? To allow more aircraft in the sky.

      There you have it... the simple definition of RVSM. Now, let's get technical:

      179238233_rvsmexample.thumb.jpg.7dec5a890cb6b0df0630858cc6783e10.jpgRVSM stands for Reduced Vertical Separation Minima and it's located between FL290 (29,000ft) until FL410 (41,000ft) inclusive. To understand RVSM, you must first understand what the vertical separation requirements were above FL290 before 2005. Prior to RVSM, aircraft were required to be separated by 2,000 feet vertically above FL290 due the possibility of altimetry errors at the higher flight levels. RVSM airspace allows for a reduction in vertical separation between qualifying aircraft in order to allow more aircraft to operate in crowded enroute airspace thereby allowing for more efficient traffic flows. Airplanes of course move a lot faster at higher altitudes though, so it is only natural that this little amount of separation may make even the most vigilant pilot a little nervous. However, it is important to note that before implementing RVSM, aviation authorities instituted a required set of parameters that must be met in order to operate in RVSM. If any of these parameters cannot be met before entering or while operating within RVSM airspace, the aircraft is required to advise ATC and exit RVSM.

      Before we get into other details about RVSM lets recall that in many countries, the East ODD and West EVEN rule applies to vertical separation. This practice ensures that two airplanes are never assigned the same altitude flying in opposite directions. In some regions that are geographically more north/south split such as Italy or Florida for example, they have elected to modify the rule to favor North ODD and South EVEN as the determining factor for vertical separation. Either way a region chooses to separate traffic, it is important to recognize that these rules exist are crucial to establishing a baseline for high altitude vertical separation.

      Now that we have covered the basic rule for opposite direction vertical separation, let's talk about what makes an aircraft RVSM approved. In order for an aircraft to operate in RVSM airspace, a certification is required from the governing agency of that nation (FAA, local CAA's, etc.), but the basic equipment that an aircraft should have operational include: an autopilot, two independent altimeters, a transponder with an altitude reporting capability, and an altitude alerting system. During flight in RVSM airspace, pilots will cross check their two independent altimeters to ensure the difference does not exceed a specified tolerance, which could range anywhere between 50ft to 200ft.  If any of these items malfunction during flight in RVSM airspace, notification to air traffic control is essential.

      Let's talk about air traffic controller's responsibilities in regards to RVSM airspace. Aircraft will have an equipment code in their flight plan assuring ATC that they are RVSM compliant and capable. If an aircraft alerts that they are no longer RVSM capable, ATC will have to either ensure separation of 2,000ft with that aircraft at all times or descend the aircraft outside of RVSM (below FL290).  However, just because an aircraft is not RVSM capable does not mean they can never fly between those altitudes. Many corporate jets are not RVSM capable but still request to cruise above RVSM airspace (e.g. FL430). In this scenario, the controller will climb the aircraft through RVSM airspace while ensuring 2,000ft separation is maintained between other traffic at all times. 

      On a final note, RVSM aircraft require a maintenance certification as well. The next time you start up your flight sim and connect to POSCON for IMG_20190825_235257469.thumb.jpg.8e83b29248a45ce99a0d2db21142efb2.jpgyour online flight simulation experience, take a look at the outside of your aircraft. Depending on the quality of the aircraft in terms of realism and study level, you should see what's called an RVSM critical area (see image to the right). Aircraft maintenance technicians must run specific tests and certify that everything located within this box meets the required RVSM tolerances, which are often stricter than in flight checks accomplished by pilots. Static ports, pitot tubes, and AOA vanes are small examples of what can be found in these boxes, of course, these are important functions that will assure RVSM tolerances when in flight. Pilots check this box during preflight inspections to ensure this critical area is free of residue, damage, dents, or other non-normal appearances on the components in the boxed lines.

      On POSCON, our air traffic controllers are well trained on RVSM procedures. When flying online, ensure your aircraft is RVSM capable and make sure you indicate it properly in the flight plan equipment code section ("W" is the letter identifying that the aircraft RVSM capable). If you do not include "W" and are offered an RVSM altitude (it happens), simply say to ATC "Negative RVSM". And of course if you are having issues with your autopilot, now you know you are required to tell air traffic control.

      After reading this article, you should be confident answering when and why the "W" equipment code is required in your flight plan. It is true, there are far too many acronyms in the aviation world, but at least you got RVSM down! See you on POSCON in RVSM and don't forget the whiskey! (get it?)


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