An air traffic controller’s primary responsibility is to separate aircraft flying under IFR. Yes, controllers have many other ancillary roles that include helping circumnavigate adverse weather, but it’s not their priority to provide a pilot with weather guidance. Nevertheless, controllers do make an attempt to assist pilots around weather when workload permits.
Let’s take a look at the challenges that controllers face in the National Airspace System (NAS) and how to best work with them to minimize your exposure to adverse weather.
If you're not already a subscriber, what are you waiting for? Subscribe today to get the issue as soon as it is released in either Print or Digital formats.
Subscribe Now
At the macro level, you’ll find air traffic controllers located at the 21 Air Route Traffic Control Centers (ARTCCs) and at various approach control facilities that serve one or more airports throughout the United States and its territories.
Lastly, there are controllers that spend their day in the cab at hundreds of ATC towers. Center controllers are those that typically talk to pilots in the airspace that is “in between” their departure and destination airports. They also control the high altitude sectors and fill in the gaps between approach control radars at lower altitudes. Center can “own” a much larger airspace from the surface up to and including 60,000 feet, according to the FAA. Approach control facilities, on the other hand, have a much smaller region of control, usually about 50 miles or so within the vicinity of a major airport, and a maximum altitude of 23,000 feet.
While this system between pilots and controllers normally works quite well even when stretched to its capacity, throw weather into the mix and it can bring the system to a grinding halt. Out of all of the curveballs that controllers deal with every day, weather has the most significant impact. Low ceilings and poor visibility often add stress on the system for departing or arriving aircraft.
But the real culprit is the presence of widespread areas or lines of deep, moist convection that can produce severe or extreme turbulence and low-level wind shear. These widespread thunderstorms or even building towering cumulus can gobble up high-impact airspace and shut down major airports for extended periods of time. This engenders delays in the NAS.
Throughout their shift, controllers are requested to solicit pilot weather reports (PIREPs) pertinent to flight safety during certain conditions. According to the FAA Order JO 7110.65W, these include:
- Ceilings at or below 5,000 feet
- Visibility (surface or aloft) at or less than 5 miles
- Thunderstorms and related phenomena
- Turbulence of moderate degree or greater
- Icing of light degree or greater
- Wind shear
- Volcanic ash clouds
- Detection of sulfur gases associated with volcanic activity, in the cabin
- Braking action advisories are in effect
Out of all of these, controllers are especially interested in moderate or greater turbulence, convective activity, and icing. From the FAA’s perspective, PIREPs have become a top safety item over the last few years, especially those that are associated with turbulence. In the coming decade as the skies get busier and weather gets more energized in association with climate change, turbulence injuries (and deaths) will undoubtedly be on the rise. Keep in mind, however, the FAA is mostly tuned into the heavy iron crowd and less focused on those of us flying light GA aircraft.
We all have likely heard the stories of pilots asking for deviations around convective weather and controllers denying that request. Either the pilot is flying in busy airspace and any deviation for weather will create a potential loss of separation with other IFR aircraft, or the controller sees nothing on their weather radar and does not understand why a deviation is even necessary. Both of these create an unfortunate situation for the pilot that is about to get pounded by severe or even extreme turbulence.
I asked Luke Alcorn, a flight instructor and air traffic controller at the Jacksonville, Florida, ARTCC, about the latency in the radar depiction available to center controllers. “If you have datalink weather [SiriusXM or FIS-B radar], you are pretty much seeing what center controllers see,” Alcorn said.
In other words, don’t expect the center controllers to provide you with better weather guidance than you can get with datalink weather. Of course, if you have onboard radar, you are way more informed than any controller with respect to convective precipitation. In fact, Alcorn said that center controllers cannot see light precipitation, storm cell tracking, wind shear, and echo tops, whereas these are available to most other ATC facilities.
Most importantly, don’t blindly assume that controllers can always see the weather directly in front of you. Unlike Alcorn, most controllers are not also pilots. In addition to the items just mentioned, they also can’t see clouds, and ATC radar cannot directly detect turbulence. Consequently, they don’t see that building towering cumulus cloud that you are about to penetrate that may contain severe or extreme turbulence as you fly through it.
Unless it is producing some form of precipitation, without reports from pilots, the controller sees this as perfectly clear air. Moreover, that airspace then becomes fair game for the controller even though it might be a really rough ride for you.
Essentially, they are in the dark until a pilot speaks up. In times of extreme weather or in busy airspace, the controller may have to turn down or even turn off the weather radar just to clearly see aircraft returns on their scope, so you can’t always rely on their help for weather avoidance.
If you must deviate around convective weather, Alcorn suggests not to wait until the very last minute. Ask for deviations and advice long before you need it.
Here’s a pro tip: If you find yourself regularly needing heading changes of more than 30 degrees, you are too close to the weather and making decisions too late. In most cases you should be deviating by 10 to 15 degrees while en route. Yes, if you need a 60-degree deviation to maneuver around a building cell, do it. But just keep that habit to a minimum. It will help lower your blood pressure and make the controller’s job much easier when deviations are small. And if you have onboard radar, let the controller know when you request a deviation.
Alcorn also offered some additional tips for pilots when needing a deviation around weather. First and foremost, be assertive. That is, don’t just say, “I need a deviation around weather.” Tell the controller how far you need to deviate left or right of course during your first transmission. Also, let them know how long you will need this deviation (e.g., 15 miles). Your call should sound something like this, “Jax center, Cessna 34B needs 10 degrees left for weather for the next 15 miles.”
Even better, look at your multifunction display or iPad and find a fix ATC can use. For example, “Jax center, Cessna 34B needs 10 degrees left for weather until passing the Chesterfield VOR in 15 miles.” This helps ATC coordinate your route with other facilities, and it may require that your route be amended in the system or handed off to another controller if the deviation places you outside of its sector.
One important tip that is worth emphasizing: You are the PIC. If for some reason you strongly feel that you must deviate to avoid an encounter with severe or greater convective turbulence and the controller denies your initial request to deviate, then you must take action, even if that means a potential loss of separation with other IFR aircraft. Simply broadcast, “PAN-PAN, Cessna 34B needs an immediate 10-degree deviation to the right for severe weather ahead,” and make the deviation you need if you feel there’s a potential for a significant encounter with injury-causing turbulence.
Again, this should be done as early as possible so that the facility can coordinate this with other facilities or move other aircraft around to avoid any loss of separation. In high-impact airspace, this can be a very stressful situation for both the pilot and controller. Due to the extremely transitory nature of convective weather, buildups from deep, moist convection occur quite often and are fundamentally impossible to predict where they will develop along your route of flight. Therefore, learning how to work with ATC in these situations is an important skill to master.
Centers primarily use NEXRAD to show precipitation on their sector suite displays. Essentially an external company contracted with the FAA creates the mosaic, and that is sent to En Route Automation Modernization (ERAM) and can be displayed by controllers. This is the system that replaced the 40-year-old En Route Host computer and backup system.
Back in 2017, the ARTCCs updated their NEXRAD product referred to as the Selectable Mosaic Generator (SMG). It has a 1-kilometer horizontal resolution. The update rate has a range from 30 seconds to five minutes and provides controllers with better altitude filtering.
The latter is primarily so controllers can reduce clutter on their scope especially for high altitude sectors. The legacy Baseline Mosaic Generator (BMG) produced precipitation mosaics that had a five-to-10-minute latency, limited coverage range, and fixed altitude strata. Center controllers also enjoy the luxury of having the Center Weather Service Units (CWSUs) looking over their shoulders. The CWSUs monitor and provide weather forecasts and advisories to the nation’s 21 ARTCCs mentioned earlier.
Colocated with air traffic controllers, these face-to-face, on-the-spot briefings convey a variety of weather information to controllers and are vital in helping them safely and efficiently route traffic. No, meteorologists at the CWSUs don’t literally look over a controller’s shoulders but are able to issue Center Weather Advisories (CWAs) to capture the adverse weather threats that evolve within their airspace. These forecasters also collaborate with the Aviation Weather Center (AWC) to provide a consistent weather message to pilots and controllers alike.
Approach control radars have a much greater refresh rate and are not dependent on an outside contractor to provide their precipitation mosaic. All of this weather data comes through the Airport Surveillance Radar (ASR) system installed at many airports. These radars are typically located on the field at the primary airport and are a dual fan-beam Doppler radar. They not only are good at identifying the location of aircraft, but they also have a weather data channel, optionally integrating six-level precipitation reflectivity data onto the controller’s display.
The rotation speed of an ASR-9 for weather detection is 12.5 revolutions per minute or 4.8 seconds for each revolution. This means the approach controller is looking at a fairly recent depiction of the precipitation falling from the base of the cloud with a refresh rate of 30 seconds (Note: A Weather Systems Processor upgrade has been made to some ASRs, adding Doppler wind velocities and an improved update rate). The effective range of these approach radars is 55-60 nm.
In addition to the ASR-9, some approach control facilities have access to the Terminal Doppler Weather Radar (TDWR). These are located near airports susceptible to low-level wind shear events such as those from microbursts and gust fronts. For example, a microburst alert can automatically be generated by the radar, and that becomes available to the controller through a ribbon display that can be passed along to pilots approaching the airport (including satellite airports).
In the end, remember that air traffic controllers are on your team. They really do want you to get to your destination as safely and efficiently as possible. Keep in mind, however, when there’s a disruption in the usual flow of air traffic due to weather, separation workload is generally greater than normal, and controllers can quickly become task saturated and unable to provide timely advisories with respect to weather.
The environment can change rapidly, forcing high-impact airports to alter the direction of their operation when surface winds shift. Something as simple as this can have a ripple effect throughout the NAS.
This feature first appeared in the May Issue 958 of the FLYING print edition.
