FR24 coverage in flight

[moari b]

I want to know why FR24.COM can operate in flight at FL38,000ft and you can see maps track aircraft. Yet why on the ground that the planes or aircraft disappear after certain ALT. Yet Flightawarecom you can see the a/c at these FL

[F-EGLF1]

I want to know why FR24.COM can operate in flight at FL38,000ft and you can see maps track aircraft. Yet why on the ground that the planes or aircraft disappear after certain ALT. Yet Flightawarecom you can see the a/c at these FL

The signal is highly directional and "line of sight " and as the antenna is on the underside of the aircraft it becomes harder to get a signal at low altitude as the aircrafts body and wings block it unless the reciever is very close to the airfield, I am within a mile of my local airfield and regularly see aircraft on the ground, with FA it may be that there is a local reciever feeding data or they may just be interpolating the track (ie guessing where it is)