Tracking airliners from space
By Tom Risen|July/August 2017
The FAA-mandated Automatic Dependent Surveillance-Broadcast network will track aircraft more accurately than today’s radars, but this approach of equipping planes to broadcast their GPS coordinates comes with an Achilles’ heel. An aircraft must be flying in range of an FAA ground station and tower for these ADS-B messages to enter the air navigation network. One of the technologists working to solve that problem is Vincent Capezzuto, the chief technology officer of Aireon, the Virginia- based joint venture of Iridium and Nav Canada. Aireon plans to plug those gaps by installing ADS-B receivers on Iridium’s next generation satellites and relaying the ADS-B messages from one satellite to the next and down to a customer’s tracking network. Capezzuto has unique perspectives on the history and status of aircraft surveillance, having worked at the FAA for nearly two decades. I spoke with Capezzuto on the phone after Aireon unveiled flight tests with Nav Canada that vetted its new surveillance data.
IN HIS WORDS
This space-based surveillance model arose from a series of opportunities that came together. Iridium happened to be changing their infrastructure and had space to put an Automatic Dependent Surveillance-Broadcast receiver on each Iridium NEXT satellite. Why is that important? I don’t think anyone would have deployed a satellite infrastructure with just an ADS-B function. The business case would have been very difficult.
Surveillance coverage gaps
Space-based ADS-B offers a bird’s-eye view looking down. We will see through the nooks and crannies; we will fill the gaps. Those are critical nooks and crannies in a lot of places. If you can’t deploy an ADS-B ground station and tower, like in the Rocky Mountains or up in Alaska, this is a solution set that provides you a service that can create surveillance where it never was before.
Automatic Dependent Surveillance-Broadcast versus ADS-Contract
The flight management system integrated with FANS-1/A [Future Air Navigation System-1/A] coupled to the aircraft communication and reporting system ACARS, provides the mechanism for transmission of messages to the ground. These transmissions can be accomplished with VHF, HF or satellite communication links and the message types are either air traffic control or airline operational. The ADS-C message is an automated pilot report of position and would be considered an air traffic control type message that would share the communication pipe with airline operational data. It’s automation of pilot reporting over a multipurpose communication link.
Why is ADS-C important? Just imagine a train going by my office right now as we’re talking; I’m yelling into the phone and you’re catching every other word. That’s what [voice communications] sometimes is like between a controller and a pilot. The communication isn’t always perfect, especially over the oceans. You’re using the high frequency links from World War II or before.
ADS-C works, but it’s noisy and it has delay in it. For surveillance, it’s as long as 180 seconds. That’s a fair amount of time for planes that are moving fast. We have an update interval of eight seconds and a latency of two seconds.
Preventing more lost flights like MH370
The International Civil Aviation Organization put out a mandate: All assets need to be tracked by the airlines with a 15-minute update interval, and in distress mode it should be able to increase the update interval to one minute. That’s the easy part for us because we surveil ADS-B, and ADS-B is already transmitting the information once a second. We can provide a one-minute update interval all the time, and you don’t even have to consider the 15-minute one. That’s great, but the second piece of the Malaysia Airlines case has to do with the ability to not turn off the transponder. Because we never found the wreckage, you really can’t say what exactly happened.
So the question is, could we have prevented it. I would tell you that with this capability and technology, we will know when someone shuts off a transponder. That would be one of those distress triggers. If someone shuts it off, all you will know is that’s the last hit I have. I’m not going to say 100 percent we would have prevented it.
Benefits beyond safety
Safety programs are very difficult to quantify. You have to say, “How many lives did we save?” or “What’s the target level of safety in the airspace?” It really is esoteric and difficult to do a cost-benefit analysis, which is typically how people make a business decision. You look at your return on an investment and you say, “I’m going to invest X. How many years does it take for me to break even?” So from any air navigation provider perspective, we’ve talked about efficiency in the airspace for the airlines. If they improve their services, they should be able to reduce the separation. Safety becomes qualitative and built into the decision as an additional unquantified benefit.
Aireon’s data is encrypted, it’s not like you can easily break into it. It’s not grounded in one location so we’re not vulnerable to someone snipping off one teleport network. We have multiple teleport networks to ground that data in, so that’s geographic diversity. The data that comes off one aircraft does not necessarily follow the same path every second. Our system is the internet in the sky, and essentially the information coming off an aircraft is composed into packets, and the packets are distributed across the multiple-satellite network, hopping from satellite to satellite before it gets grounded. So an unauthorized person can’t recompose the information. We can, because we know what the packets look like and we understand the packet design. Then we put it into one place, and then we have to decrypt it, and then we have to compile it, put it all back together, to create the target position. Then on the space side, first of all, 1090 MHz is being transmitted by aircraft in the clear as an open, nonencrypted message, and we have the ability to receive it. We’re 485 miles up in space, so it’s not like someone is going to be perturbing the signal. What they could perturb is the GPS signal, not the ADS-B signal. And that is, again, a known phenomenon that, working at the FAA and understanding how the air navigation service providers work, may have other solutions.
So FAA officials have the appropriate protocols and emergency response plans to deal with those scenarios. In fact, I would argue that our system will be able to detect a worldwide GPS jamming session very quickly, because essentially we’re monitoring aircraft, aircraft that are transmitting GPS information.