Keeping you safe is a big deal for us—the biggest. Air Traffic Control exists to separate aircraft from each other, from terrain, and from obstacles. We work from dawn to dawn, 24/7, 365 days a year, watching the skies and making decisions that protect you in our National Airspace System (NAS).
We have tools and rules to accomplish this? That control is based on many factors, including radar procedures, non-radar procedures, rules and regulations, plus a strong infrastructure that supports each of these techniques.
From the moment you get your clearance to the moment you make your landing, ATC watches and works with you to make your flight as safe as it can be. Your every move and our every clearance is in furtherance of this goal. In this article we’re going to explore the radar tools we use to accomplish our jobs in the radar environment and some of the different types of separation.
Separation Standards
Every action and every move made by ATC is governed by one rule: Don’t lose separation.
This prerogative is king amongst all things air traffic control. When we clear you off the ground, there is separation built into the clearance. When we you climb you to a new altitude, there is separation. When we reroute you or turn you, there is separation.
At all times when you are in the sky and receiving ATC services some, or many, rules are applied to assure you’re separated from all other air traffic. We use a myriad of separation standards to accomplish this. Some are based on radar information depicted on our radar scopes and some are considered “non-radar” which use specific rules to ensure separation.
Separation standards are governed by the FAA Order 7110.65, or “Point Sixty-Five” as we ATC’ers call it. The Point Sixty-Five contains every rule and requirement for air traffic control. It outlines all controller responsibilities, including off-shore/oceanic procedures, emergency procedures, handling of Special Flights, traffic management procedures, Canadian Airspace Procedures, weather dissemination, and every rule that relates to separation. The Point Sixty-Five is the holy bible of ATC.
Since we can’t go into every single topic of separation, we’re going to focus on the main standards of radar separation.
ATC Radar
Before we talk about the details of radar separation we should talk about the primary tools we use to accomplish this method of separation.
ATC radar is a rather complex and boring topic to really dig into from a technical perspective, but it is an interesting topic to discuss in general. Radar sites are peppered throughout the United States. Currently there are over 750 ground-based radar systems that serve as the backbone of surveillance in the NAS. These short-range surveillance radar systems are comprised of “cooperative radars” that identify and track aircraft with the help of on-board aircraft transponders, and “non-cooperative radars” that identify and track an aircraft’s position independently, without the use of on-board transponders.
We call cooperative radar “secondary radar,” while we call non-cooperative radar “primary radar.” The reason for this is that primary radar is the default kind of radar that ATC uses to see aircraft in the sky. Primary radar relies on a broadcasted signal being reflected, or “bounced back” by aircraft. This is a physical radar return that is depicted on ATC radar scopes. Secondary radar “cooperates” with aircraft using transponder technology that sends out interrogation pulses from the ground station which are received by the aircraft transponder, causing the aircraft to automatically send a reply signal containing identification and altitude information.
Additionally, you have the more modern types of systems that provide radar data to air traffic controllers. The most prolifically used of these are ADS-B and WAM (Wide Area Multilateration). WAM is a cooperative aircraft surveillance technology based on the same time difference of arrival principle that is used on an airport surface. WAM is a technique where several ground receiving stations listen to signals transmitted from an aircraft; then the aircraft’s location is mathematically calculated—typically in two dimensions, with the aircraft providing its altitude. If this sounds familiar, that’s because it is a type of secondary radar, like transponders. ADS-B, on the other hand, sends out more detail about an aircraft than your standard transponder.
Despite the prolific adoption and use of ADS-B and radar and WAM, the need for primary radar systems still remains crucial. Unfortunately, structural deficiencies and maintenance-related issues are becoming more frequent and apparent with primary radar systems. This obviously introduces more risk to the system. Older radar systems require more frequent repairs, leading to increased costs and periods when the system is not operational. This increases the risk of delayed or cancelled flights.
The FAA recently (August 7th, 2024) initiated a “Radar Modernization Proposal” that plans to enhance the safety and efficiency of the National Airspace System by avoiding costly and inconvenient delays, consolidating radar systems to reduce costs, providing continued support for Department of Defense and Department of Homeland Security missions, continuing support General Aviation aircraft that haven’t adopted ADS-B technologies, and also (perhaps most important in this day and age) provide an increase in cybersecurity capabilities. The President’s FY 2025 FAA budget proposal calls for a dedicated capital investment of $8 billion over the next five years to replace aging facilities and modernize 377 critical radar systems that average 36 years of age.
Radar Separation
Under the current rules and regulations in the Point Sixty-Five, radar separation depends largely on how close aircraft are to the radar site and the type of radar surveillance that the site provides.
For terminal radar controllers (Terminal Radar Approach Control or “TRACON”), the radar rotates or “sweeps” at a faster rate. This makes the radar returns more accurate because of the reduced time between sweeps. There is less lag and a tighter margin of variance. Therefore, TRACON controllers are able to get aircraft closer together and provide a more efficient flow of traffic. The standard lateral separation for TRACON controllers is three miles. Vertical separation is 1000 feet.
En-route controllers (Center controllers) typically receive radar information that is older due to the slower radar sweeps and length of time it takes for the signals to return to the radar site. This requires them to maintain at least five miles of lateral separation between aircraft. Vertical separation for enroute controllers is also 1000 feet.
The Point Sixty-Five includes many “non-radar” rules that are based on time, distance, divergence, and a number of other very particular factors to ensure separation. This method of separation is more commonly used in Towers by using timed departures and runway separation, but they are also used in the radar environment to ensure separation from uncontrolled airport departures and arrivals.
Practically Speaking
I know all this separation information and semi-technical explanation of our radar systems is riveting … but let’s get real and talk about what it looks like while you’re flying along and working with the wonderous professionals on the other side of the radio.
We’ll look at two common scenarios. First, we’ll look at a departure from a Class C airport where you get radar services right after taking off. Then we’ll look at a departure from a non-towered airport where you conduct quite a bit of the departure phase before getting into radar contact with a TRACON or Center controller. Both scenarios utilize the same sort of radar identification and provide the same radar services.
The requirements for controllers conducting radar identification are outlined in the Point Sixty-Five. There are multiple methods of radar identification. This gives controllers options when they need to radar identify an aircraft. Having multiple methods is important because sometimes the most common method is unavailable.
The most common method is through identifying the aircraft by the discrete beacon code assigned to them in their clearance. This code is transmitted, received by our radar systems, and displayed on ATC radar scopes. The controller already has all the information on your flight in their system and the computer is able to process the incoming radar data and connect your beacon code to the information displayed on the radar screen.
Some of the other ways that controllers can radar identify an aircraft (according to the Point Sixty-Five) are:
Observing a departing aircraft target within one mile of the takeoff runway end at airports with an operating control tower.
Observing a target with respect to a fix (displayed on the video map, scribed on the map overlay, or displayed as a permanent echo) or a visual reporting point (whose range and azimuth from the radar antenna has been accurately determined) corresponds with a direct position report received from an aircraft, and the observed track is consistent with the reported heading or route of flight visually.
Observing a target make an identifying turn or turns of 30 degrees or more.
Observing an ident or requesting the pilot to squawk “standby” and observing the target disappear for a sufficient number of radar scans.
There is one more method that is unique to Center controllers. For Center controllers, an aircraft may be considered radar identified when the full data block is automatically associated with the target symbol of an aircraft that is squawking a discrete code.
After radar identification, a unique “data tag” will be attached to your radar target, either manually or automatically.
This data tag contains critical pieces of information about your flight. Obviously, it has your callsign. It also contains your altitude information that has been transmitted from your outgoing Mode C. There is also ground speed information that helps radar controllers anticipate your future location based on speed and trajectory.
TRACON and Center have different types of computer systems that process flight plans and radar information, so depending on which facility is working you at the moment, additional information might be displayed in the data tag. Sometimes it’s your destination, sometimes it’s your aircraft type, sometimes it’s nothing. If the controller wants to simplify the data tag display they can select the minimum amount of information. But at the very least, controllers must have the callsign and altitude information in order to utilize a data tag and radar target to conduct separation of the aircraft.
Now that you have a rudimentary understanding of radar identification, let’s take a look at the two scenarios you can encounter during two different circumstances.
Class C Airports
N13DZ is flown by a student pilot working on his insrument rating. He is flying solo from the Class C airport KCOS to KALS where he will take a short break and then fly back to KCOS. He’s done all his due diligence in pre-planning and filing his IFR flight plan. He’s consumed his mandatory multiple cups of coffee, conducted his preflight inspection, and gone through all his preflight checklists. He’s contacted clearance delivery, received his IFR clearance, and has received taxi instruction to the runway. He’s cleared for take-off and off he goes.
Shortly after departing the runway and starting his climb, N13DZ is told to “Contact departure, 134.5.” At this time, N13DZ is NOT receiving radar services. The only form of separation ensuring safety is based on visual separation and “non-radar” separation rules associated with the IFR clearance and Tower separation rules. There are pages upon pages in the Point Sixty-Five on the rules that controllers can utilize to ensure separation in these manners. Lucky for you, this is an article on radar separation and we won’t spend the next ten days talking about all of that.
Once N13DZ contacts departure, the departure controller will utilize any one of the myriad of methods to radar identify him. Only then will N13DZ begin receiving radar services.
After this, all of the radar information and technology is used to track N13DZ will be utilized to monitor and control the flight for the duration of the leg.
Non-Towered Airports
Now let’s look at the non-towered airport KALS, when N13DZ receives clearance back to KCOS.
N13DZ calls the Center controller and requests his clearance. The controller issues the clearance, including a discrete beacon code to squawk. N13DZ takes off and conducts the ODP for KALS. The ODP for KALS requires the pilot to navigate to the ALS VORTAC and continue the climb in the ALS VORTAC holding pattern until reaching 16,000.
This is a unique procedure that is based almost entirely on the limited primary radar coverage for the San Luis Valley. This limited coverage has been all but erased by ADS-B, but when ADS-B is unavailable ATC cannot see the aircraft on radar until they are (nearly) at or above 16,000 feet. The radar site that services the area is located on the east side of the Sangre de Cristo Mountains and does not have line of sight with the aircraft departing the San Luis Valley until they are above the peaks of the mountains.
Either way, once N13DZ is in radar coverage (whether ADS-B or primary radar) he will be radar identified by ATC. Because he is squawking a discrete beacon code, the data tag will auto-acquire to the radar target and the controller will be off to the races providing radar services.
So now you know a bit about radar and standard separations in the radar environment. There are many things that go into the simple act of separating aircraft, and ATC is always vigilant in their utilization of rules and tools to ensure your safety.
Mac Lawler has been a writer for many years and enjoys the privilege of entertaining and educating with his words. He is an optimist, a romantic, and as Carl Jung would put it, a seeker.
