Very interesting replies on here as I often wondered why some aircraft appeared in odd places, I was tacking my daughters flight to Berlin last night and FR 24 followed down the LHR Taxiways to the holding point and then the take off. At the same time another BA flight was seemingly landing on the yet to be built third runway at LHR. I had always assumed these were sort of random FR24 errors and it was interesting to read the causes of some of these anomalies . One of the things that has always amused me about it is the occasional aircraft going backwards in flight which is obviously not the case but I assume is just one of several parameters acting up . Its not perfect but its pretty amazing what you can now track from your living room
PB