Is RADAR Controller the senior position and RADAR Associate the junior position? That is, does one normally progress from Associate to Controller? How long does it take to progress from one to the next? Is it common/expected for people in your position to move to different airports?
Radar Controllers and Radar Associates are just staffing positions.
Some background information to build on…
An Air Traffic Controller's job title when they start out is Air Traffic Control Specialist. An Air Traffic Control Specialist starts out in the AG pay band (Academy Graduate). When that Controller gets certifications, they move up to the D1 pay band (Developmental), then to D2, D3, and when they get all of their certifications or "fully certify", they end in the CPC pay band and their job title changes to Certified Professional Controller.
The Radar Controller position is also called the R-side, and the Radar Associate position is also called the D-side. A trainee needs to certify on all of their D-sides before they start training on their R-sides.
So basically the answer to your first two questions is "yes". However there can be a more experienced controller working the D-side while a new controller is working the R-side. The Air Traffic Controllers rotate through the different positions throughout the day. It is based on when someone arrives for their shift, or comes back to the control room from their break, they check with the controller that has been on a position the longest, and asks that person if they want a break. If not, the Controller moves on to the next person who has been working the longest, and so forth.
ARTCCs or Air Route Traffic Control Centers or just "Centers", are divided into "specialties" (or "areas") that controllers are assigned to. Each specialty is divided into sectors. At the minimum, each sector needs to staffed by a Radar Controller. If the sector is busy with a lot of traffic or is complex due to weather events, or maybe traffic being rerouted from another sector, then a Radar Associate position will be staffed at that sector. If traffic is very light, for example in the middle of the night, sectors can be combined and one Radar Controller will work multiple sectors and talk to multiple aircraft on different frequencies.
The time it takes to get certified depends on many factors. It could be anywhere from one month, to six months. From starting out to get fully certified, can take anywhere between two years, to five years. It depends on many factors, such as personal ability, training opportunities, training backlogs, etc.
It is common for people to switch facilities at least once. Some stay at their first facility, some move several times. When a Controller graduates from the FAA's training facility (that's where "Academy Graduate" comes from), they are given a short list of facilities to chose from. The list constantly changes based on the FAA's staffing needs.
The FAA does do "direct hires" for people with previous ATC experience (usually through military) directly into certain facilities, but a new hire without experience won't know where they'll go when they start out.
The views expressed here are my own and not necessarily those of FAA.
What expertise is it that ATC folks build up in all of those years of training? Is it knowledge of plane behavior by model, familiarity with the region, radar behavior? Or is the majority of it the less tangible “getting a feel for the flow of traffic to instinctively pick out unusual behavior”?
(Edit to my parent comment: " It could be anywhere from one month, to six months" to certify on a single sector, but it's really more like one to three months.)
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All of the above.
Whenever an Air Traffic Controller transfers to a new facility, or even transfers to a new specialty within a facility, they have to train and get certified on all of the new sectors. Each sector is different due to traffic flow, types of traffic, equipment limitations, etc.
For the Houston Center Ocean specialty, equipment familiarization is very important for Controllers. There are 5 sectors: Ocean West, Ocean East, Offshore West, Offshore Central, and Offshore East. Ocean West and East deal primarily with aircraft flying between the United States and Mexico. There are different airways that aircraft can take, and each one has different characteristics (crossing airways, airways defined by RNAV fixes vs bearings off of VORTACs, radio coverage, and radar coverage).
In the Offshore sectors, radio coverage is harder to manage. There are multiple transmitters and receivers that are located on different offshore platforms, and the ocean elements and weather can affect the equipment. At our positions next to the radar scopes, there are touchscreens with many different buttons to select which frequencies we want to monitor, transmit on, use primary or backup sites, etc. Most sectors do not have to toggle between different transmitters, but in the Offshore sectors, that's a common occurrence. There are also different transmitter sites for the Ocean sectors, so we commonly get pilots saying that they're losing us on the radio when we are talking to another aircraft a hundred miles away, and we can hear the pilot just fine.
In the Ocean sectors, radar doesn't cover the middle of the Gulf of Mexico, so we have to rely on aircraft position reports unless they have ADS-B.
At HCF Center, there are mountains which block radar coverage, so it's good to know where we can expect to lose or establish radar contact with aircraft.
Yes, there is an element of becoming familiar with the routine traffic. You see many of the same flights every day, so you know where they are going. It got to the point at HCF Center, where if someone told me a flight number, I could tell them the departure and destination airports without looking.
However, just like pilots, Air Traffic Controllers cannot let routine turn into complacency. We can never just assume anything, if we are unsure, we have to ask or restate something. Safety is our number one priority.
The views expressed here are my own and not necessarily those of the FAA.