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I was keeping an eye on a friend's flight on PlaneFinder. It was meant to be flying past my office, so I walked to the window to see (the airport is about a minute away when they pass, so it's pretty low). However it was about two minutes later that the plane went past.

What gives? I can't see flight sites showing it in advance, but on the map it was showing it low over Richmond, Vancouver and inline with my building - it would be incredibly hard for me to mis-read the map, but I can't think of any other option.

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I know it's fun, but is this really travel-related? These apps don't have much practical use to a traveller; I would have thought this would sit better on one of the mobile-device-specific SE sites... –  Andrew Ferrier Sep 28 '12 at 10:36
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3 Answers

up vote 7 down vote accepted

There's a service called Flightradar24, and they have this to say in the description:

In addition to ADS-B data, we also get data from the Federal Aviation Administration (FAA) in the United States. This data is based on radar data and includes all commercial air traffic in US and Canadian air space (i.e. not just planes with ADS-B transponders). Unlike the ADS-B data that is presented real-time, the FAA data is delayed by roughly 5 minutes due to FAA regulations.

ADS-B stands for Automatic dependent surveillance-broadcast, a GPS-based surveillance system that broadcasts a signal with plane's position in real time and can be intercepted by anyone with the necessary equipment.

From the PlaneFinder FAQ, they use the same ADS-B information that FlightRadar does, and I imagine every similar service under the sun.

I assume the FAA is the only source of flight information in US and Canada, so similar applications would use the same database, and with the same delay.

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I have this iPad App that lets you monitor live flights feed. One of the great features is that you point your iPad to a contrail and it tells you the details of that specific flight. As you can see on the example below there is some delay of seconds, probably caused by the internet feeds of the different information sources enter image description here

I would consider that live though.I have only tried this app in Europe, but there the responses seems to be accurate.

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The flight tracker websites actually have an incentive to not be exactly correct, and they argue that this is for security.

The cynical mind would suggest it just gives them a bit of a cost saving when it comes to information polling, updates etc.

Generally they will be within five minutes or so and reasonably accurate on flight paths (around here they seem to be within a few hundred feet)

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Not entirely true. Modern aircraft are equipped with anADS-B system which broadcasts the plane position in real time and the signal can be received and interpreted by anyone. Assuming the data acquisition is in close-to-real time, it's not only a question of security-through-obscurity. See this page for some more info. –  mindcorrosive Sep 26 '12 at 7:27
    
Agreed, but the question asked about these websites- and they don't need to pass you real time info. –  Rory Alsop Sep 26 '12 at 9:23
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