Residents of our northern Wilmington suburbs periodically get upset about the noise from low-flying airplanes on their way to the Philadelphia airport, but this only happens occasionally when the powers that be temporarily change the flight paths. At those times, the planes continuously fly overhead about one minute apart. Just as one disappears over the horizon you can hear the sound of another approaching. But I enjoy this, and often step outside to watch them. Then, after about an hour, they suddenly stop, rerouted somewhere else, and no others are seen until the next unpredictable change maybe a day or a week later. These brief flurries of activity seem to occur only on summer evenings, but that could be when I most tend to notice them.
I especially enjoy watching them from my backyard lawn chair in the twilight of a warm summer evening. The cabin and landing lights are on, and I can imagine the excited activity inside preparing for the landing. I am not bothered by the noise, thanks to my hearing loss that does have some advantages. But, I often wonder, where they are coming from? From a Caribbean resort or a faraway economic hub?
This summer I will no longer have to wonder. I found an app for my Nexus tablet (see posting of 12/16/2013) that shows in real time moving airplane icons on a Google map that I have set for my area. I could set the location for anyplace in the world, not just the USA. However, my tablet is WiFi only, so I am pretty much limited to backyards. Click on any of the icons and it will show the flight number, its origin and destination, its flight track, a photo of the plane itself, and its speed and altitude.
You may recognize this as the aircraft version of the British hobby of trainspotting.
You can see how it works on your own computer at http://www.flightradar24.com/ You will be surprised by the number of flights nearby. Many are just unnoticed specks high in the sky. The computer version has all of the features. The free app version is stripped-down, bare-bones, but the purchased version is only $2.99, so go ahead and splurge.
You can change the screen refresh rate, but I leave mine at the standard 8 seconds. Like all GPS data, it takes a few seconds of movement to determine the direction and speed, but the initial screen usually tells me all I want to know. You can even select a realistic simulation of a live view from the cockpit window that works better on the app than on the website.
The planes track their own position by GPS, and continuously transmit that data to surrounding aircraft and ground receivers by an on-board transponder. This new system, Automatic Dependent Surveillance-Broadcast (ADS-B), is replacing radar for aircraft tracking, and all planes must have it by 2020. The system allows them to see and avoid other aircraft in their area wherever they are, even far from a radar site. Many amateurs in isolated areas pick up the data on their own receivers and relay it to a central collection site. Because the transmissions travel by line-of-sight, they cannot bend over the horizon and are limited to a distance of about 200 miles, depending on the altitude of the plane. Aircraft that generally do not have ADS-B are helicopters, military aircraft, prop planes, business jets, and older aircraft. And, as you would expect, Air Force One, at least nothing we can tap into.
The ADS-B system seems to be the transponder that was mysteriously turned off on the missing Malaysian plane. The system has been mentioned as a possible replacement or augmentation of the black box that must be retrieved after a crash.