Are the live flight radar websites *actually* live?
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.
Best Answer
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 
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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Is Flightradar24 in real-time?
Flightradar24: Live Flight Tracker - Real-Time Flight Tracker Map.Where does Flightradar24 get its data?
Flightradar24 combines data from several data sources including ADS-B, MLAT and radar data. The ADS-B, MLAT and radar data is aggregated together with schedule and flight status data from airlines and airports to create a unique flight tracking experience on www.flightradar24.com and in Flightradar24 apps.Can we track flight live?
Check Flight Status It doesn't matter whether you are travelling domestic or international, with the help of flight tracker, you can anytime track your flight and see if there are any changes in the scheduled timings.Is Flight Aware real-time?
The data displayed on FlightAware.com is typically 30 seconds delayed from real-time. Maps animate the aircraft position toward the last known position. An aircraft's position on the map may lag real-time by 1-2 minutes. Depending on the data source, updates are usually one to four times a minute.5 Best Websites for Live Flight Tracking
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Answer 2
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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