US NextGen Air Traffic Control

When most people think about aviation, they would associate it with highly advanced state of art technologies working together to make flying safe and efficient. While flying IS safe and efficient, the systems in use are, surprisingly, far from technologically advanced currently, especially for pilots of smaller airplanes that don’t have million dollars worth of flight computers, and navigation/communication equipment.

I’ve had about 25 hours of flight time now (trying to figure out how to record my flights, so videos coming soon! hopefully), and I’m now at a point where I can shift my attention from flying the plane, to things like more advanced radio procedures and airspace control structures, etc. However, as an engineer, the more I study, the more I’m frustrated about how primitive these systems are, and how they can be easily (and inexpensively) improved to reduce pilots and controllers workload, and indirectly make flying safer.

Fortunately, as I’ve just found out, the ATC system in the US is getting a major overhaul in the next couple years (most of the ground infrastructure is already operational), with a lot of very cool improvements. The biggest difference, in my opinion, is now planes will be tracked.

First, some background information on how the US (sorry, I have no idea what Canadian airspace is like) airspace is laid out –

US Airspace

For pilots, the big blue sky is actually divided into a lot of different segments controlled by different controllers (controllers are people on radio and radar who keep track of where airplanes are, and tell them where to go, so they can get to where they want to go, without crashing into other planes).

In the US, there are 3 classes of controllers – control towers, TRACONs (terminal radar approach controls), and ARTCC (air route traffic control centers).

Stationed at each airport (or busier airports at least) is a control tower. They give take-off and landing clearances, as well as routing traffic around the airport’s immediate vicinity.

At high altitude, flights are controlled by area controllers (ARTCC, also known as “Centers”), who direct flights in the en-route phase to their destinations, passing them from center to center.

And then there are TRACONs that transition flights from en-route (center) to terminal area (airport control towers).

For example, in San Jose, most of the city is covered by Mineta San Jose International Airport’s airspace at low altitude, and San Francisco International’s airspace at high altitude. SFO airspace is a lot bigger because it’s a very busy airport. This can be seen on the chart here – SkyVector. The magenta lines define SJC airspace, and the big blue circles define SFO airspace.

Above the control towers is NorCal Approach, which is the TRACON that handles all low altitude traffic in northern California. I believe they are based in Sacramento. Huge concrete building with no windows.

Then on top of that is Oakland Center, which is the ARTCC that handles high altitude traffic in most of California and neighboring states.

Plane Tracking – Current System

Since air traffic controllers need to provide everyone with traffic separation service and advisories (ok, that’s not really true, but we’ll ignore that for now), they need a way to figure out where everyone is.

Right now, there are 2 types of radar in use – primary radars, and secondary surveillance radars (SSR).

Primary radars are what we normally call radars – they send out a signal, and figure out where aircrafts are based on reflections, but they can’t find out any other information about the aircraft. Notably, altitude information cannot be accurately derived, and altitude happens to be very important for separating planes.

Secondary radars, on the other hand, relies on aircrafts’ cooperation to the radar’s interrogation signals. Most aircrafts are equipped with a transponder, that, when queried by the SSR, will reply with the aircraft’s altitude, as well as a 4 digit code that can be assigned by an ATC.

There are several problems with this approach:

  1. Some planes won’t be seen on radar – planes flying too low, behind obstacles, or F-22s sneaking through (even though they are not on stealth missions).
  2. Primary radars are expensive to maintain.
  3. Airplanes cannot see each other (airliners and some advanced general aviation planes have SSRs, called Traffic Collision Avoidance Systems, but those are very expensive), and must rely on controllers to relay traffic information.
  4. No other information about planes are transmitted by the transponder – call sign (unique identifier for each airplane), type, speed, etc. To be able to uniquely identify aircrafts, ATCs need to explicitly assign identifier codes (“squawk”) to each aircraft, which is not optimal, since aircrafts all already have unique identifiers.

Plane Tracking – NextGen

In the NextGen ATC system, most of the primary radars will be decommissioned. Instead, airplanes will be required to have transmitters that continuously transmit their GPS coordinates and other information to ground radio stations.

Ground stations will then consolidate all the position reports, as well as planes detected by primary radars, and make them available to both ATCs and pilots.

This way, everyone can have reliable traffic information, with just a simple receiver and display. No expensive TCAS is needed.

With the newly established data link, ground stations will also be able to transmit weather information to aircrafts.

Current State

Currently, most of the ground stations are operational already, with a deadline of 2013. However, the ground stations are only one part of the story. The other part relies on plane owners to install compliant transmitters (ADS-B, Automatic Dependent Surveillance – Broadcast), to transmit their own information. Nowadays, about half of airliners have ADS-B capabilities, while extremely few general aviation airplanes do. FAA has set a deadline of 2020 for aircraft owners, though. After 2020, virtually all aircrafts will be required to have ADS-B.

I looked into building a simple receiver to receive traffic information, but noticed FAA did something sneaky.

Basically, they won’t send you traffic information if you don’t have ADS-B capabilities. The official reason is that knowing your position will allow them to only send you traffic in your vicinity. I believe the real reason is to encourage people to install ADS-B transmitters sooner.

It’s too bad that we can’t just build a receiver to receive traffic information, but that will change by 2020 at the latest.

Will be very exciting to fly in the US in the future!