Perhaps some of you are familiar with "The Praxis Foundation". If not, I invite you to meander your way over to one of my adjacent sectors on the right column. You may note the seemingly paradoxical subject of their article about ADS-B and the required ground stations required for what is being sold to the public as a more efficient space-based airplane tracking system. The new trend in aviation technology development (aka: NextGen) is to fund the heck out of idea and then wait around a decade or two for the results. The hardest part is not being disappointed by the end.
Disappointment is inevitable, however. The companies who bid for the initial development funding are naturally going to promise the world to us on a silver platter. They probably even intend to deliver what they promise. But I'm not here to talk about promises. I'm here to talk about expectations and results. I actually don't even want to talk about expectations, but I have no choice than to bring them up to frame the subsequent, inevitable disappointments.
ADS-B - What I expected and how reality stacks up:
Let me start by saying that most controllers, myself included, do not see radar as a limitation to capacity. Now that I write that, I bet you couldn't find a controller who would think that. ADS-B is in use in Louisville, KY with UPS, but I don't know anywhere who works there.... Ok, let me rephrase: I don't think you can find a Center controller who thinks radar is a limitation to capacity.
In Boston Center, we have a significant portion of our airspace, below FL180, certified for reduced lateral (3NM instead of 5NM required) separation. A lot of work goes into getting 3NM airspace. It gets justified by saying "but we can run planes that much closer, which means we can run more in the same amount of space!". Three miles is great when you're on a small range running a bunch of planes in a straight line (like, say, an approach control). In my area, the scope is generally configured to be 200 miles from one side of the scope to the other. The computer symbol that displays the location of the airplane is about 1 mile wide. So you want me to run 3 miles apart!? At 450 knots ground speed!? Nobody does that intentionally. Very often, the wind at one end of my sector will be significantly different speed and from a different direction than the other end. And its changing at the speed of the wind (50-200 mph). There needs to be a buffer so when one plane enters the area of more headwind and slows down, he doesn't get run over by the plane still goes much faster right behind. The point is, we don't need less than 5NM in the en-route environment. So, I don't expect ADS-B to help me increase capacity. I am obligated to bring up the point that the MAIN factor in increasing capacity and reducing delays is adding runways that we can land on every day.
I won't just dismiss this as a waste of time, however. As a controller who isn't completely under-layed by approach controls (I "own to the ground") I am acutely aware of the limitation of my radar and where I have no coverage at low altitudes. So, when I heard about "space-based tracking" (ADS-B), I was excited that one day I'd be able to see all of my planes all of the time. I expected that such a space-based system would look down over the world, send a signal down to the planes, receive a reply back, and then the satellite would beam down the data to our scopes. It would be able to see everyone with an operating transponder. This assumed system would not be able to fully replace radar, since planes in distress sometimes loose their transponders in some form. We wouldn't be able to assist planes when they needed our help the most.
But, that isn't how it currently works.....
As of right now, I am getting mixed messages. Boston Center ran a test a few months ago to see how our ADS-B coverage compared to our normal radar coverage. ADS-B is required to have coverage that is the same or better as radar. But ADS-B is not certified to be used in places we currently don't have radar coverage or within areas we use 3NM. It is also not designed to see places radar can't. If we show an improvement, that is strictly convenient. Currently, ADS-B is used in Alaska and over the Gulf of Mexico (these places don't have good radar coverage). If you are confused, join the club. But what about those damn satellites!? Can't they see everyone!?
Well, my expectation don't meet the reality. Did you read the Praxis article about all of those ground based sensors? The "space-based" part isn't anything other than good ole' GPS that the airplanes use to navigate today. So, how it works:
Step 1 - The plane's GPS figures out where it is and converts that data into coordinates.
Step 2 - The new, super-awesome, transponder in the plane takes those coordinates, throws in pressure altitude data, aircraft ID info, and maybe even some other data that ATC isn't going to use, and, every second, beams it down to a ground based sensor. Think cell phone tower........
Step 3 - That data collected by the ground based sensor goes off to a server somewhere and distributes the data to places that need it. The aforementioned altitude, location and ID data ends up in a an FAA computer which then sends it to our scopes. (This last step may be slightly simplified)
When you drive your car to the airport using a GPS on your phone or dashboard, you are equally, if not more "NextGen", than the flight you're about to board. Luckily, you are much less likely to get lost since there are actual people making sure you don't make a wrong turn. These people also help you avoid traffic jams and accidents. Its very convenient.
Safety - Why I'm not writing it off yet....
We already have a network of ground sensors in place. They exist. We used them in February for a test. They work. So, how can we use them to make the system safer?
First, planes with ADS-B will be able to see other ADS-B equipped planes around them. Callsigns and everything. The ground sensors can transmit traffic information (TIS-B) out to planes to display on their own screens. If your plane is out of range of a sensor, some systems will be able to receive the data via relay through other nearby airplanes that are in a location or at an altitude that is within range of a sensor. Some sensors will also include FIS-B, which would transmit new NOTAMs, AIRMETS and/or SIGMETS for the area.
The push now is to give controllers the ability use high altitude planes to relay information to and from planes out of radar and sensor coverage. The concern from the developers is that all of this relaying back and forth would take up too much bandwidth. That's fine. Just give us an ERAM function to toggle the function on and off. We just need one or two at a time to fill in the gaps. We don't need all the planes to be relaying back and forth to all the other planes. We get it. Just let us switch between one, and then maybe another when we need it. If the next space-based system is supposed to razzle and dazzle us, then it should be an improvement! The next system should make us wonder how we ever lived with just radar. And I say "just radar" because you can't ever turn radar off if you want to maintain safety. And that's a controllers primary concern. Safety. We are supposed to be there when you need us. We need to be able to see you if you want our help. It's our job to think of reasons ADS-B can't be the only way or else someone who doesn't care about safety is going to make it the only way.
Reasons we can't get rid of radar:
1 - Terrorists turn off the transponder.
2 - Plane looses electrical power
3 - Attenuation.
4 - For that matter, a huge tornado takes out some sensors....
5 - ADS-B antennae get covered in five inches of rime ice.
6 - Lightning?
7 - Power outage at ground sensor
8 - Hackers
9 - Solar Flares
Got more? Leave a comment.
Reasons why ADS-B increases safety of flight:
1 - Increases pilot awareness.
2 - Allows controllers to provide expanded traffic separation and advisory services.
3 - Is a great backup to radar.
4 - Is very accurate over a larger area (radar gets less exact the farther away from the antennae you go).
Got more? Leave a comment.
As a taxpayer, perhaps your first question should be: "why didn't we design a system which met the goals of the second list, with an emphasis on safety of flight?" Surely that would be much less expensive and the project would have had a clear goal. Can't help ya there, sorry. I'm busy working planes; not enough time to alter the universe.
I will add here, before I go, that ADS-B will enable future programs to safely integrate ways to increase efficiency. Wow, I should get a job as a NextGen salesmen...... Seriously, though - there is testing in the works that will allow planes to safely run closer together and/or to sequence themselves in a fuel efficient manner using the data that is relayed back and forth between the planes as I mentioned above (Imagine the Perfect Vector, where planes always went exactly 5 miles behind another when crossing over SYR. Or, using speed, planes approach the active runway perfectly staggered on opposite base legs, ready for the final controller to put them 3 miles apart on final.) Imagine it. Some controllers would feel threatened. Others would imagine the economy recovering at some point and the task of working twice as many planes as we do now. We're gonna need some help.....
Till next time....
PS. The airlines were totally on board with this program until they realized that the government wasn't going to buy the new fancy transponders and traffic screens for them. Suddenly, it wasn't such a great money saving piece of NextGen technology. Planes equipped with ADS-B are few and far between at this point. ERAM envisions a world where almost all planes have ADS-B. When a plane doesn't have it installed or operating, a little red A appears on our scope next to the plane. Luckily, we can turn them off, since they are everywhere. So, ERAM can dream....but it is still learning how to make a handoff to New York approach. :) Due to furlough and supposedly resolved issues with NY which delayed it, ERAM at Boston Center is postponed until after the end of the year, or when furlough ends. Or whenever.....
PPS. Oh, by the way. ADS-B stands for Automatic Dependent Surveillance - Broadcast. If you asked.