I am outside on the street watching PIA flight 785 from Islamabad’s Benazir Bhutto Airport fly over Berlin enrout to London Heathrow. It is a Boeing 777-300ER traveling at 36.000 feet at over 400 knots per hour.

I looked at the contrails and the mighty iPhone did the rest. Thanks to ADS-B. gathers ADS-B-information form thousands of aircraft all over the world and projects them on a map in real time. If this is combined with the location service of the iPhone (it knows where it is, sometimes better than me…), the contrails in the sky become a particular airliner. Magic if I ever saw it!

So what is ADS-B?

In the sky it is very important to know where you are. Aviation at large has that one figured out pretty good. Maps, VOR, GPS, Radar controllers and more high-tech systems like inertia navigation have pretty much taken care of position awareness.

The problem is, figuring our where everybody else is!

Mid-air collisions are rare but the more devastating when they happen. And they are surprisingly difficult to avoid. The sky is very large and aircraft are very fast. Even more so if two of them are moving towards each other. Even in perfect visual conditions, it can be hard to see oncoming traffic in time. Let alone at night or in the clouds.

Because of that, Airliners have had a collision avoidance system for years. The standard is called TCAS (Traffic Alert and Collision Avoidance System) and it is very cool. Traffic will not only be displayed in the cockpit. The respective TCAS-systems of two airliners will actually talk to each other, determine the best way to avoid any close calls and make recommendations for actions to resolve a possible conflict, to their flight crews.

ADS-B is TCAS for the rest of us. The remarkable thing is that it basically combines parts of the existing infrastructure to create a valuable, additional service.

ADS-B is a communication standard which utilizes the transponder (identification transmitter) of a general aviation aircraft and feeds the location information from the on-board GPS into it. Genius! So now my transponder sends out “this is me” plus “this is where I am”. All of a sudden, I can receive the transponder information of other aircraft around me and display their positions on my GPS screen. And since the technical step is relatively small, many pilots are upgrading their hardware to ADS-B capability.

Additional services, like weather information, is also broadcasted via ADS-B and can also be displayed on the GPS screen. This makes the system even more popular.

I look up to the sky again and I wonder again, where the jet above my head is heading for. I might check, or maybe I will just dream for a moment.

To be continued…


(originally posted on June 18, 2012 by tilbo at

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