Antonio,
Aircraft with ADSB can be error checked to make sure that we show the correct information from them. Non ADSB equipped aircraft cannot be error checked in the same way so sometimes we get for example the wrong fight ID showing or the wrong flight ID being applied to an aircraft. To stop this we look for consecutive messages back from the aircraft as the result of interogation by ground based radars before the flight ID is displayed. We tried it initially requiring 5 consecutive messages with the call sign. This was good in ensuring that the correct call sign was applied to the correct aircraft. While this worked fine in areas for example busy airport terminal areas, in areas of limited radar coverage and even at cruising altitude in some busier areas there was less interogation so less messages returned which meant that getting even 5 consecutive messages with the correct information was quite hard.
We settled at 2 consecutive messages and while this works in most cases, you may get the occasional incorrect information displayed for flight ID and a few aircraft at the extreme range of your coverage may not get displayed on the grid as insufficent messages are received. Other receivers use the same approach to error checking non ADSB equipped aircraft
Please note this only applied to non-ADSB equipped aircraft. ADSB equipped aircraft as stated earlier have error checking applied which cuts out this error. ADSB equipped aircraft send out, squit, detailed information every second or so and dont rely on interogation from ground based radar.
We have given users the choice of whether to turn it off or on. If you are located in a busy terminal area on or off will not make to much difference but if your located more remotely, having it on may reduce flight ID errors at the risk of some aircraft transiting the extreme edges of your coverage not displaying on the grid. Its one of those settings for user choice and trialing to see what gives them the best results.
Alan
